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  • Unable to boot from LiveCD/USB and even Super Grub Disk!

    - by Reuben L.
    Hi all, I'm in a fix. Basically this morning, I decided to format my Win7 as it was getting really slow and I did so with no problems. I also have a Linux Mint OS on dual boot. Since I was springcleaning my windows partition, I decided it was a good idea to do the same to my linux partition. I downloaded the latest version of Linux Mint (Julia) and burned the LiveCD. Now here is where the problem lies, when I restarted Windows and chose to boot from the LiveCD, it didn't work. No joke. There was just a little underscore blinking for a long time before it went back to GRUB which prompted me to select an OS to boot. However, when I went into my old Linux Mint OS and restarted the machine, the LiveCD worked... to a certain extent. It would load and look as though it was ready to install Linux Mint 10 but the moment it got to the option screen, the whole screen turned into a checkered and jumbled mess. At this point I thought it was the LiveCD or the .iso file. I had an Ubuntu LiveUSB for recovery purposes and I tried that. The exact same thing happened. Can't boot the LiveUSB if I restarted from Windows, but works when I reboot from Linux. BUT still the same checkered screen that doesnt respond. Did a bit of googling and reckoned it might be something wrong with my GRUB. Did some updating and didnt make a difference. Then I tried the Super Grub Disk and STUPIDLY uninstalled GRUB. (Note that booting to SGD had the exact same problem - can't be done if I rebooted from Windows). Now I can't access my Linux Mint 9 cos the the bootup screen (mbr) only has Windows 7 as an option. Remember me mentioning that I can't boot from any CD/USB/recovery CD when I reboot from Windows? And now that I can't access Linux, there's no way for me to do any form of recovery! I've tried using the command prompt utility at startup recovery but to no avail. Anyone can help me with this?

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  • Formal Languages, Inductive Proofs &amp; Regular Expressions

    - by MarkPearl
    So I am slogging away at my UNISA stuff. I have just finished doing the initial once non stop read through the first 11 chapters of my COS 201 Textbook - “Introduction to Computer Theory 2nd Edition” by Daniel Cohen. It has been an interesting couple of days, with familiar concepts coming up as well as some new territory. In this posting I am going to cover the first couple of chapters of the book. Let start with Formal Languages… What exactly is a formal language? Pretty much a no duh question for me but still a good one to ask – a formal language is a language that is defined in a precise mathematical way. Does that mean that the English language is a formal language? I would say no – and my main motivation for this is that one can have an English sentence that is correct grammatically that is also ambiguous. For example the ambiguous sentence: "I once shot an elephant in my pyjamas.” For this and possibly many other reasons that I am unaware of, English is termed a “Natural Language”. So why the importance of formal languages in computer science? Again a no duh question in my mind… If we want computers to be effective and useful tools then we need them to be able to evaluate a series of commands in some form of language that when interpreted by the device no confusion will exist as to what we were requesting. Imagine the mayhem that would exist if a computer misinterpreted a command to print a document and instead decided to delete it. So what is a Formal Language made up of… For my study purposes a language is made up of a finite alphabet. For a formal language to exist there needs to be a specification on the language that will describe whether a string of characters has membership in the language or not. There are two basic ways to do this: By a “machine” that will recognize strings of the language (e.g. Finite Automata). By a rule that describes how strings of a language can be formed (e.g. Regular Expressions). When we use the phrase “string of characters”, we can also be referring to a “word”. What is an Inductive Proof? So I am not to far into my textbook and of course it starts referring to proofs and different types. I have had to go through several different approaches of proofs in the past, but I can never remember their formal names , so when I saw “inductive proof” I thought to myself – what the heck is that? Google to the rescue… An inductive proof is like a normal proof but it employs a neat trick which allows you to prove a statement about an arbitrary number n by first proving it is true when n is 1 and then assuming it is true for n=k and showing it is true for n=k+1. The idea is that if you want to show that someone can climb to the nth floor of a fire escape, you need only show that you can climb the ladder up to the fire escape (n=1) and then show that you know how to climb the stairs from any level of the fire escape (n=k) to the next level (n=k+1). Does this sound like a form of recursion? No surprise then that in the same chapter they deal with recursive definitions. An example of a recursive definition for the language EVEN would the 3 rules below: 2 is in EVEN If x is in EVEN then so is x+2 The only elements in the set EVEN are those that be produced by the rules above. Nothing to exciting… So if a definition for a language is done recursively, then it makes sense that the language can be proved using induction. Regular Expressions So I am wondering to myself what use is this all – in fact – I find this the biggest challenge to any university material is that it is quite hard to find the immediate practical applications of some theory in real life stuff. How great was my joy when I suddenly saw the word regular expression being introduced. I had been introduced to regular expressions on Stack Overflow where I was trying to recognize if some text measurement put in by a user was in a valid form or not. For instance, the imperial system of measurement where you have feet and inches can be represented in so many different ways. I had eventually turned to regular expressions as an easy way to check if my parser could correctly parse the text or not and convert it to a normalize measurement. So some rules about languages and regular expressions… Any finite language can be represented by at least one if not more regular expressions A regular expressions is almost a rule syntax for expressing how regular languages can be formed regular expressions are cool For a regular expression to be valid for a language it must be able to generate all the words in the language and no other words. This is important. It doesn’t help me if my regular expression parses 100% of my measurement texts but also lets one or two invalid texts to pass as well. Okay, so this posting jumps around a bit – but introduces some very basic fundamentals for the subject which will be built on in later postings… Time to go and do some practical examples now…

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  • Gene Hunt Says:

    - by BizTalk Visionary
    "She's as nervous as a very small nun at a penguin shoot"   "He's got fingers in more pies than a leper on a cookery course" "You so much as belch out of line and I'll have your scrotum on a barbed wire plate" "Let's go play slappyface" "your surrounded by armed barstewards" “Right, get out and find this murdering scum right now!” [pause] “Scratch that, we start 9am sharp tomorrow, it's beer-o-clock.” "So then Cartwright, you're such a good Detective.... Go and Detect me a packet of Garibaldies" "You're not the one who is going to have to knit himself a new arsehole after 25 years of aggressive male love in prison" “A dream for me is Diana Dors and a bottle of chip fat." “A dream for me is Diana Dors and a bottle of chip fat." “They reckon you've got concussion - but personally, I couldn't give a tart's furry cup if half your brains are falling out. Don't ever waltz into my kingdom playing king of the jungle.” “You great... soft... sissy... girlie... nancy... french... bender... Man-United supporting POOF!!” “Drugs eh? What's the point. They make you forget, make you talk funny, make you see things that aren't there. My old grandma got all of that for free when she had a stroke.” “He's Dead! It's quite serious!” “Fanny in the flat...Nice Work” “SoopaDoopa” “Tits in a Jumper!” “Drop your weapons! You are surrounded by armed bastards!” “It's 1973, almost dinnertime. I'm 'avin 'oops!” “Trust the Gene Genie!” “I wanna hump Britt Ekland...What're we gonna do...!” “Was that 'E' and you don't know the rest?! or you going 'Eeee, I Dunno'” “Good Girl! Prostate probe and no jelly. “ “Give over, it's nothing like Spain!” “I'll come over your houses and stamp on all your toys!” “The Wizard will sort it out. It's cos of the wonderful things he does” “Cartwright can jump up and down on his knackers!” “It's not a windup love, he really thinks like this!” “Women! You can't say two words to them” “I was thinking, maybe, a Berni Inn!” “If I wanted a bollocking for drinking too much...!” “Shhhh...hear that...that's the sound of this case being closed! “Chicken!? In a basket!?” “Seems a large quantity of cocaine...” “You probably thought he kept his cock in his keks!” “The tail-end of Rays demotion speech!” “Stephen Warren is gay!?” “You're a smart boy, use your initiative!” “Don't be such a Jessie!” “I find the idea of a bird brushing her teeth...!” “Never been tempted to the Magic talcum powder?” “Make sure she's got nice tits!” “You're more likely to find an ostrich with a plum up it's arse!” “Drink this lot under the table and have a pint on the way home!” “Never be a female Prime Minister!” “Pub? Pub! pub!.....Pub!” “Thou shalt not suck off rent boys!” “The number for the special clinic is on the notice board!” “If me uncle had tits, would he be me auntie!” “Got your vicars in a twist!” “We Done?!” “Your mates got balls...If they were any bigger he'd need a wheelbarrow!” “The Ending - from 'I want to go home' to the end music.”

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  • problem occur during installation of moses scripts

    - by lenny99
    we got error when compile moses-script. process of it as follows: minakshi@minakshi-Vostro-3500:~/Desktop/monu/moses/scripts$ make release # Compile the parts make all make[1]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts' # Building memscore may fail e.g. if boost is not available. # We ignore this because traditional scoring will still work and memscore isn't used by default. cd training/memscore ; \ ./configure && make \ || ( echo "WARNING: Building memscore failed."; \ echo 'training/memscore/memscore' >> ../../release-exclude ) checking for a BSD-compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking for gawk... no checking for mawk... mawk checking whether make sets $(MAKE)... yes checking for g++... g++ checking whether the C++ compiler works... yes checking for C++ compiler default output file name... a.out checking for suffix of executables... checking whether we are cross compiling... no checking for suffix of object files... o checking whether we are using the GNU C++ compiler... yes checking whether g++ accepts -g... yes checking for style of include used by make... GNU checking dependency style of g++... gcc3 checking for gcc... gcc checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking dependency style of gcc... gcc3 checking for boostlib >= 1.31.0... yes checking for cos in -lm... yes checking for gzopen in -lz... yes checking for cblas_dgemm in -lgslcblas... no checking for gsl_blas_dgemm in -lgsl... no checking how to run the C++ preprocessor... g++ -E checking for grep that handles long lines and -e... /bin/grep checking for egrep... /bin/grep -E checking for ANSI C header files... yes checking for sys/types.h... yes checking for sys/stat.h... yes checking for stdlib.h... yes checking for string.h... yes checking for memory.h... yes checking for strings.h... yes checking for inttypes.h... yes checking for stdint.h... yes checking for unistd.h... yes checking n_gram.h usability... no checking n_gram.h presence... no checking for n_gram.h... no checking for size_t... yes checking for ptrdiff_t... yes configure: creating ./config.status config.status: creating Makefile config.status: creating config.h config.status: config.h is unchanged config.status: executing depfiles commands make[2]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/memscore' make all-am make[3]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/memscore' make[3]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/memscore' make[2]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/memscore' touch release-exclude # No files excluded by default pwd=`pwd`; \ for subdir in cmert-0.5 phrase-extract symal mbr lexical-reordering; do \ make -C training/$subdir || exit 1; \ echo "### Compiler $subdir"; \ cd $pwd; \ done make[2]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/cmert-0.5' make[2]: Nothing to be done for `all'. make[2]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/cmert-0.5' ### Compiler cmert-0.5 make[2]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/phrase-extract' make[2]: Nothing to be done for `all'. make[2]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/phrase-extract' ### Compiler phrase-extract make[2]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/symal' make[2]: Nothing to be done for `all'. make[2]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/symal' ### Compiler symal make[2]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/mbr' make[2]: Nothing to be done for `all'. make[2]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/mbr' ### Compiler mbr make[2]: Entering directory `/home/minakshi/Desktop/monu/moses/scripts/training/lexical-reordering' make[2]: Nothing to be done for `all'. make[2]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts/training/lexical-reordering' ### Compiler lexical-reordering ## All files that need compilation were compiled make[1]: Leaving directory `/home/minakshi/Desktop/monu/moses/scripts' /bin/sh: ./check-dependencies.pl: not found make: *** [release] Error 127 We don't know why this error occurs? check-dependencies.pl file existed in scripts folder ...

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  • How to rotate a set of points on z = 0 plane in 3-D, preserving pairwise distances?

    - by cagirici
    I have a set of points double n[] on the plane z = 0. And I have another set of points double[] m on the plane ax + by + cz + d = 0. Length of n is equal to length of m. Also, euclidean distance between n[i] and n[j] is equal to euclidean distance between m[i] and m[j]. I want to rotate n[] in 3-D, such that for all i, n[i] = m[i] would be true. In other words, I want to turn a plane into another plane, preserving the pairwise distances. Here's my code in java. But it does not help so much: double[] rotate(double[] point, double[] currentEquation, double[] targetEquation) { double[] currentNormal = new double[]{currentEquation[0], currentEquation[1], currentEquation[2]}; double[] targetNormal = new double[]{targetEquation[0], targetEquation[1], targetEquation[2]}; targetNormal = normalize(targetNormal); double angle = angleBetween(currentNormal, targetNormal); double[] axis = cross(targetNormal, currentNormal); double[][] R = getRotationMatrix(axis, angle); return rotated; } double[][] getRotationMatrix(double[] axis, double angle) { axis = normalize(axis); double cA = (float)Math.cos(angle); double sA = (float)Math.sin(angle); Matrix I = Matrix.identity(3, 3); Matrix a = new Matrix(axis, 3); Matrix aT = a.transpose(); Matrix a2 = a.times(aT); double[][] B = { {0, axis[2], -1*axis[1]}, {-1*axis[2], 0, axis[0]}, {axis[1], -1*axis[0], 0} }; Matrix A = new Matrix(B); Matrix R = I.minus(a2); R = R.times(cA); R = R.plus(a2); R = R.plus(A.times(sA)); return R.getArray(); } This is what I get. The point set on the right side is actually part of a point set on the left side. But they are on another plane. Here's a 2-D representation of what I try to do: There are two lines. The line on the bottom is the line I have. The line on the top is the target line. The distances are preserved (a, b and c). Edit: I have tried both methods written in answers. They both fail (I guess). Method of Martijn Courteaux public static double[][] getRotationMatrix(double[] v0, double[] v1, double[] v2, double[] u0, double[] u1, double[] u2) { RealMatrix M1 = new Array2DRowRealMatrix(new double[][]{ {1,0,0,-1*v0[0]}, {0,1,0,-1*v0[1]}, {0,0,1,0}, {0,0,0,1} }); RealMatrix M2 = new Array2DRowRealMatrix(new double[][]{ {1,0,0,-1*u0[0]}, {0,1,0,-1*u0[1]}, {0,0,1,-1*u0[2]}, {0,0,0,1} }); Vector3D imX = new Vector3D((v0[1] - v1[1])*(u2[0] - u0[0]) - (v0[1] - v2[1])*(u1[0] - u0[0]), (v0[1] - v1[1])*(u2[1] - u0[1]) - (v0[1] - v2[1])*(u1[1] - u0[1]), (v0[1] - v1[1])*(u2[2] - u0[2]) - (v0[1] - v2[1])*(u1[2] - u0[2]) ).scalarMultiply(1/((v0[0]*v1[1])-(v0[0]*v2[1])-(v1[0]*v0[1])+(v1[0]*v2[1])+(v2[0]*v0[1])-(v2[0]*v1[1]))); Vector3D imZ = new Vector3D(findEquation(u0, u1, u2)); Vector3D imY = Vector3D.crossProduct(imZ, imX); double[] imXn = imX.normalize().toArray(); double[] imYn = imY.normalize().toArray(); double[] imZn = imZ.normalize().toArray(); RealMatrix M = new Array2DRowRealMatrix(new double[][]{ {imXn[0], imXn[1], imXn[2], 0}, {imYn[0], imYn[1], imYn[2], 0}, {imZn[0], imZn[1], imZn[2], 0}, {0, 0, 0, 1} }); RealMatrix rotationMatrix = MatrixUtils.inverse(M2).multiply(M).multiply(M1); return rotationMatrix.getData(); } Method of Sam Hocevar static double[][] makeMatrix(double[] p1, double[] p2, double[] p3) { double[] v1 = normalize(difference(p2,p1)); double[] v2 = normalize(cross(difference(p3,p1), difference(p2,p1))); double[] v3 = cross(v1, v2); double[][] M = { { v1[0], v2[0], v3[0], p1[0] }, { v1[1], v2[1], v3[1], p1[1] }, { v1[2], v2[2], v3[2], p1[2] }, { 0.0, 0.0, 0.0, 1.0 } }; return M; } static double[][] createTransform(double[] A, double[] B, double[] C, double[] P, double[] Q, double[] R) { RealMatrix c = new Array2DRowRealMatrix(makeMatrix(A,B,C)); RealMatrix t = new Array2DRowRealMatrix(makeMatrix(P,Q,R)); return MatrixUtils.inverse(c).multiply(t).getData(); } The blue points are the calculated points. The black lines indicate the offset from the real position.

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  • How to attach turrets to tiles in a tile based game

    - by Joseph St. Pierre
    I am a flash developer, and I am building a Tower Defense game. The world is being built through tiles, and I have gotten that accomplished easily. I have also gotten level changes and enemy spawning down as well. However, I wish the player to be able to spawn turrets, and have those turrets be on specific tiles, based upon where the player placed it. Here is my code: stop(); colOffset = 50; rowOffset = 50; guns = []; placed = true; dead = 0; spawned = 0; level = 1; interval = 350 / level; amount = level * 20; counter = 0; numCol = 14; numRow = 10; tiles = []; k = 0; create = false; tileName = new Array("road","grass","end", "start"); board = new Array( new Array(1,1,1,1,3,1,1,1,1,1,2,1,1,1), new Array(1,1,1,0,0,1,1,1,1,1,0,1,1,1), new Array(1,1,1,0,1,1,1,1,1,1,0,0,1,1), new Array(1,1,1,0,0,0,1,1,1,1,1,0,1,1), new Array(1,1,1,0,1,0,0,0,1,1,1,0,0,1), new Array(1,1,1,0,1,1,1,0,0,1,1,1,0,1), new Array(1,1,0,0,1,1,1,1,0,1,1,0,0,1), new Array(1,1,0,1,1,1,1,1,0,1,0,0,1,1), new Array(1,1,0,0,0,0,0,0,0,1,0,1,1,1), new Array(1,1,1,1,1,1,1,1,0,0,0,1,1,1) ); buildBoard(); function buildBoard(){ for ( col = 0; col < numCol; col++){ for ( row = 0; row < numRow; row++){ _root.attachMovie("tile", "tile_" + col + "_" + row, _root.getNextHighestDepth()); theTile = eval("tile_" + col + "_" + row); theTile._x = (col * 50); theTile._y = (row * 50); theTile.row = row; theTile.col = col; tileType = board[row][col]; theTile.gotoAndStop(tileName[tileType]); tiles.push(theTile); } } } init(); function init(){ onEnterFrame = function(){ counter += 1; if ( spawned < amount && counter > 50){ min= _root.attachMovie("minion","minion",_root.getNextHighestDepth()); min._x = tile_4_0._x + 25; min._y = tile_4_0._y + 25; min.health = 100; choose = Math.round(Math.random()); if ( choose == 0 ){ min.waypointX = [ tile_4_1._x +25, tile_3_1._x + 25, tile_3_2._x + 25, tile_3_6._x + 25, tile_2_6._x + 25, tile_2_8._x + 25, tile_8_8._x + 25, tile_8_9._x + 25, tile_10_9._x + 25, tile_10_7._x + 25, tile_11_7._x + 25, tile_11_6._x + 25, tile_12_6._x + 25, tile_12_4._x + 25, tile_11_4._x + 25, tile_11_2._x + 25, tile_10_2._x + 25, tile_10_0._x + 25]; min.waypointY = [ tile_4_1._y +25, tile_3_1._y + 25, tile_3_2._y + 25, tile_3_6._y + 25, tile_2_6._y + 25, tile_2_8._y + 25, tile_8_8._y + 25, tile_8_9._y + 25, tile_10_9._y + 25, tile_10_7._y + 25, tile_11_7._y + 25, tile_11_6._y + 25, tile_12_6._y + 25, tile_12_4._y + 25, tile_11_4._y + 25, tile_11_2._y + 25, tile_10_2._y + 25, tile_10_0._y + 25]; } else if ( choose == 1 ){ min.waypointX = [ tile_4_1._x +25, tile_3_1._x + 25, tile_3_2._x + 25, tile_3_3._x + 25, tile_5_3._x + 25, tile_5_4._x + 25, tile_7_4._x + 25, tile_7_5._x + 25, tile_8_5._x + 25, tile_8_8._x + 25, tile_8_9._x + 25, tile_10_9._x + 25, tile_10_7._x + 25, tile_11_7._x + 25, tile_11_6._x + 25, tile_12_6._x + 25, tile_12_4._x + 25, tile_11_4._x + 25, tile_11_2._x + 25, tile_10_2._x + 25, tile_10_0._x + 25 ]; min.waypointY = [ tile_4_1._y +25, tile_3_1._y + 25, tile_3_2._y + 25, tile_3_3._y + 25, tile_5_3._y + 25, tile_5_4._y + 25, tile_7_4._y + 25, tile_7_5._y + 25, tile_8_5._y + 25, tile_8_8._y + 25, tile_8_9._y + 25, tile_10_9._y + 25, tile_10_7._y + 25, tile_11_7._y + 25, tile_11_6._y + 25, tile_12_6._y + 25, tile_12_4._y + 25, tile_11_4._y + 25, tile_11_2._y + 25, tile_10_2._y + 25, tile_10_0._y + 25 ]; } min.i = 0; counter = 0; spawned += 1; min.onEnterFrame = function(){ dx = this.waypointX[this.i] - this._x; dy = this.waypointY[this.i] - this._y; radians = Math.atan2(dy,dx); degrees = radians * 180 / Math.PI; xspeed = Math.cos(radians); yspeed = Math.sin(radians); this._x += xspeed; this._y += yspeed; if( this._x == this.waypointX[this.i] && this._y == this.waypointY[this.i]){ this.i++; } if ( this._x == tile_10_0._x + 25 && this._y == tile_10_0._y + 25){ this.removeMovieClip(); dead += 1; } } } if ( dead >= amount ){ dead = 0; level += 1; amount = level * 20; spawned = 0; } } btnM.onRelease = function(){ create = true; } } game.onEnterFrame = function(){ } It is possible for me however to complete this task, but only once. I am able to make the turret, drag it over to a tile, and have it attach itself to the tile. No problem. The issue is, I cannot do these multiple times. Please Help.

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  • rotate player based off of joystick

    - by pengume
    Hey everyone I have this game that i am making in android and I have a touch screen joystick that moves the player around based on the joysticks position. I cant figure out how to also get the player to rotate at the same angle of the joystick. so when the joystick is to the left the players bitmap is rotated to the left as well. Maybe someone here has some sample code I could look at here is the joysticks class that I am using. `public class GameControls implements OnTouchListener { public float initx = DroidzActivity.screenWidth - 45; //255; // 320 og 425 public float inity = DroidzActivity.screenHeight - 45;//425; // 480 og 267 public Point _touchingPoint = new Point( DroidzActivity.screenWidth - 45, DroidzActivity.screenHeight - 45); public Point _pointerPosition = new Point(DroidzActivity.screenWidth - 100, DroidzActivity.screenHeight - 100); // ogx 220 ogy 150 private Boolean _dragging = false; private boolean attackMode = false; @Override public boolean onTouch(View v, MotionEvent event) { update(event); return true; } private MotionEvent lastEvent; public boolean ControlDragged; private static double angle; public void update(MotionEvent event) { if (event == null && lastEvent == null) { return; } else if (event == null && lastEvent != null) { event = lastEvent; } else { lastEvent = event; } // drag drop if (event.getAction() == MotionEvent.ACTION_DOWN) { if ((int) event.getX() > 0 && (int) event.getX() < 50 && (int) event.getY() > DroidzActivity.screenHeight - 160 && (int) event.getY() < DroidzActivity.screenHeight - 0) { setAttackMode(true); } else { _dragging = true; } } else if (event.getAction() == MotionEvent.ACTION_UP) { if(isAttackMode()){ setAttackMode(false); } _dragging = false; } if (_dragging) { ControlDragged = true; // get the pos _touchingPoint.x = (int) event.getX(); _touchingPoint.y = (int) event.getY(); // Log.d("GameControls", "x = " + _touchingPoint.x + " y = " //+ _touchingPoint.y); // bound to a box if (_touchingPoint.x < DroidzActivity.screenWidth - 75) { // og 400 _touchingPoint.x = DroidzActivity.screenWidth - 75; } if (_touchingPoint.x > DroidzActivity.screenWidth - 15) {// og 450 _touchingPoint.x = DroidzActivity.screenWidth - 15; } if (_touchingPoint.y < DroidzActivity.screenHeight - 75) {// og 240 _touchingPoint.y = DroidzActivity.screenHeight - 75; } if (_touchingPoint.y > DroidzActivity.screenHeight - 15) {// og 290 _touchingPoint.y = DroidzActivity.screenHeight - 15; } // get the angle setAngle(Math.atan2(_touchingPoint.y - inity, _touchingPoint.x - initx) / (Math.PI / 180)); // Move the ninja in proportion to how far // the joystick is dragged from its center _pointerPosition.y += Math.sin(getAngle() * (Math.PI / 180)) * (_touchingPoint.x / 70); // og 180 70 _pointerPosition.x += Math.cos(getAngle() * (Math.PI / 180)) * (_touchingPoint.x / 70); // make the pointer go thru if (_pointerPosition.x > DroidzActivity.screenWidth) { _pointerPosition.x = 0; } if (_pointerPosition.x < 0) { _pointerPosition.x = DroidzActivity.screenWidth; } if (_pointerPosition.y > DroidzActivity.screenHeight) { _pointerPosition.y = 0; } if (_pointerPosition.y < 0) { _pointerPosition.y = DroidzActivity.screenHeight; } } else if (!_dragging) { ControlDragged = false; // Snap back to center when the joystick is released _touchingPoint.x = (int) initx; _touchingPoint.y = (int) inity; // shaft.alpha = 0; } } public void setAttackMode(boolean attackMode) { this.attackMode = attackMode; } public boolean isAttackMode() { return attackMode; } public void setAngle(double angle) { this.angle = angle; } public static double getAngle() { return angle; } }` I should also note that the player has animations based on when he is moving or attacking. EDIT: I got the angle and am rotating the sprite around in the correct angle however it rotates on the wrong spot. My sprite is one giant bitmap that gets cut into four pieces and only one shown at a time to animate walking. here is the code I am using to rotate him right now. ` public void draw(Canvas canvas,int pointerX, int pointerY) { Matrix m; if (setRotation){ // canvas.save(); m = new Matrix(); m.reset(); // spriteWidth and spriteHeight are for just the current frame showed //m.setTranslate(spriteWidth / 2, spriteHeight / 2); //get and set rotation for ninja based off of joystick m.preRotate((float) GameControls.getRotation()); //create the rotated bitmap flipedSprite = Bitmap.createBitmap(bitmap , 0, 0,bitmap.getWidth(),bitmap.getHeight() , m, true); //set new bitmap to rotated ninja setBitmap(flipedSprite); setRotation = false; // canvas.restore(); Log.d("Ninja View", "angle of rotation= " +(float) GameControls.getRotation()); } ` And then the draw method // create the destination rectangle for the ninjas current animation frame // pointerX and pointerY are from the joystick moving the ninja around destRect = new Rect(pointerX, pointerY, pointerX + spriteWidth, pointerY + spriteHeight); canvas.drawBitmap(bitmap, getSourceRect(), destRect, null);

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  • Yesterday's broken codebase hunt me back

    - by sandun dhammika
    I need a fun oky. I just love this openmoko hardware and hacking into it. Please could somebody help me to compile qemu.I 'm so sad and I want to compile qemu and it required the GCC3.x and then I downloaded gcc 3.2 but when I configure it and build it, it gives a very sad error message. G_FOR_TARGET=" "SHELL=/bin/sh" "EXPECT=expect" "RUNTEST=runtest" "RUNTESTFLAGS=" "exec_prefix=/gcc-3.2" "infodir=/gcc-3.2/info" "libdir=/gcc-3.2/lib" "prefix=/gcc-3.2" "tooldir=/gcc-3.2/i686-pc-linux-gnu" "AR=ar" "AS=as" "CC=gcc" "CXX=c++" "LD=ld" "LIBCFLAGS=-g -O2" "NM=nm" "PICFLAG=" "RANLIB=ranlib" "DESTDIR=" DO=all multi-do make[1]: Leaving directory `/gcc-3.2/gcc-3.2/zlib' make[1]: Entering directory `/gcc-3.2/gcc-3.2/fastjar' make[1]: Leaving directory `/gcc-3.2/gcc-3.2/fastjar' make[1]: Entering directory `/gcc-3.2/gcc-3.2/gcc' gcc -c -DIN_GCC -g -O2 -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long -DHAVE_CONFIG_H -DGENERATOR_FILE -I. -I. -I. -I./. -I./config -I./../include ./read-rtl.c -o read-rtl.o In file included from ./read-rtl.c:24:0: ./rtl.h:125:3: warning: type of bit-field ‘code’ is a GCC extension ./rtl.h:128:3: warning: type of bit-field ‘mode’ is a GCC extension ./read-rtl.c: In function ‘fatal_with_file_and_line’: ./read-rtl.c:61:1: warning: traditional C rejects ISO C style function definitions ./read-rtl.c: In function ‘read_rtx’: ./read-rtl.c:662:8: error: lvalue required as increment operand make[1]: *** [read-rtl.o] Error 1 make[1]: Leaving directory `/gcc-3.2/gcc-3.2/gcc' make: *** [all-gcc] Error 2 This is so sad and this is sooo bad. I have searched patches and workaround all over the Internet to this,but I couldn't find any alternative for this. I'm out of my patience now. I want that virtual machine ready and I want to make a debug host cos I don't have some money to buy original neo 1937 hardware. The patch that I have found comes with a nasty error too. I'm so sick of it.Any idea how could I fix this problem and make this work? Please please I'm begging you somebody help me please. Thanks all.

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  • 2d trajectory planning of a spaceship with physics.

    - by egarcia
    I'm implementing a 2D game with ships in space. In order to do it, I'm using LÖVE, which wraps Box2D with Lua. But I believe that my question can be answered by anyone with a greater understanding of physics than myself - so pseudo code is accepted as a response. My problem is that I don't know how to move my spaceships properly on a 2D physics-enabled world. More concretely: A ship of mass m is located at an initial position {x, y}. It has an initial velocity vector of {vx, vy} (can be {0,0}). The objective is a point in {xo,yo}. The ship has to reach the objective having a velocity of {vxo, vyo} (or near it), following the shortest trajectory. There's a function called update(dt) that is called frequently (i.e. 30 times per second). On this function, the ship can modify its position and trajectory, by applying "impulses" to itself. The magnitude of the impulses is binary: you can either apply it in a given direction, or not to apply it at all). In code, it looks like this: def Ship:update(dt) m = self:getMass() x,y = self:getPosition() vx,vy = self.getLinearVelocity() xo,yo = self:getTargetPosition() vxo,vyo = self:getTargetVelocity() thrust = self:getThrust() if(???) angle = ??? self:applyImpulse(math.sin(angle)*thrust, math.cos(angle)*thrust)) end end The first ??? is there to indicate that in some occasions (I guess) it would be better to "not to impulse" and leave the ship "drift". The second ??? part consists on how to calculate the impulse angle on a given dt. We are in space, so we can ignore things like air friction. Although it would be very nice, I'm not looking for someone to code this for me; I put the code there so my problem is clearly understood. What I need is an strategy - a way of attacking this. I know some basic physics, but I'm no expert. For example, does this problem have a name? That sort of thing. Thanks a lot.

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  • Vector math, finding coördinates on a planar between 2 vectors

    - by Will Kru
    I am trying to generate a 3d tube along a spline. I have the coördinates of the spline (x1,y1,z1 - x2,y2,z2 - etc) which you can see in the illustration in yellow. At those points I need to generate circles, whose vertices are to be connected at a later stadium. The circles need to be perpendicular to the 'corners' of two line segments of the spline to form a correct tube. Note that the segments are kept low for illustration purpose. [apparently I'm not allowed to post images so please view the image at this link] http://img191.imageshack.us/img191/6863/18720019.jpg I am as far as being able to calculate the vertices of each ring at each point of the spline, but they are all on the same planar ie same angled. I need them to be rotated according to their 'legs' (which A & B are to C for instance). I've been thinking this over and thought of the following: two line segments can be seen as 2 vectors (in illustration A & B) the corner (in illustraton C) is where a ring of vertices need to be calculated I need to find the planar on which all of the vertices will reside I then can use this planar (=vector?) to calculate new vectors from the center point, which is C and find their x,y,z using radius * sin and cos However, I'm really confused on the math part of this. I read about the dot product but that returns a scalar which I don't know how to apply in this case. Can someone point me into the right direction? [edit] To give a bit more info on the situation: I need to construct a buffer of floats, which -in groups of 3- describe vertex positions and will be connected by OpenGL ES, given another buffer with indices to form polygons. To give shape to the tube, I first created an array of floats, which -in groups of 3- describe control points in 3d space. Then along with a variable for segment density, I pass these control points to a function that uses these control points to create a CatmullRom spline and returns this in the form of another array of floats which -again in groups of 3- describe vertices of the catmull rom spline. On each of these vertices, I want to create a ring of vertices which also can differ in density (amount of smoothness / vertices per ring). All former vertices (control points and those that describe the catmull rom spline) are discarded. Only the vertices that form the tube rings will be passed to OpenGL, which in turn will connect those to form the final tube. I am as far as being able to create the catmullrom spline, and create rings at the position of its vertices, however, they are all on a planars that are in the same angle, instead of following the splines path. [/edit] Thanks!

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  • Fixed point math in c#?

    - by x4000
    Hi there, I was wondering if anyone here knows of any good resources for fixed point math in c#? I've seen things like this (http://2ddev.72dpiarmy.com/viewtopic.php?id=156) and this (http://stackoverflow.com/questions/79677/whats-the-best-way-to-do-fixed-point-math), and a number of discussions about whether decimal is really fixed point or actually floating point (update: responders have confirmed that it's definitely floating point), but I haven't seen a solid C# library for things like calculating cosine and sine. My needs are simple -- I need the basic operators, plus cosine, sine, arctan2, PI... I think that's about it. Maybe sqrt. I'm programming a 2D RTS game, which I have largely working, but the unit movement when using floating-point math (doubles) has very small inaccuracies over time (10-30 minutes) across multiple machines, leading to desyncs. This is presently only between a 32 bit OS and a 64 bit OS, all the 32 bit machines seem to stay in sync without issue, which is what makes me think this is a floating point issue. I was aware from this as a possible issue from the outset, and so have limited my use of non-integer position math as much as possible, but for smooth diagonal movement at varying speeds I'm calculating the angle between points in radians, then getting the x and y components of movement with sin and cos. That's the main issue. I'm also doing some calculations for line segment intersections, line-circle intersections, circle-rect intersections, etc, that also probably need to move from floating-point to fixed-point to avoid cross-machine issues. If there's something open source in Java or VB or another comparable language, I could probably convert the code for my uses. The main priority for me is accuracy, although I'd like as little speed loss over present performance as possible. This whole fixed point math thing is very new to me, and I'm surprised by how little practical information on it there is on google -- most stuff seems to be either theory or dense C++ header files. Anything you could do to point me in the right direction is much appreciated; if I can get this working, I plan to open-source the math functions I put together so that there will be a resource for other C# programmers out there. UPDATE: I could definitely make a cosine/sine lookup table work for my purposes, but I don't think that would work for arctan2, since I'd need to generate a table with about 64,000x64,000 entries (yikes). If you know any programmatic explanations of efficient ways to calculate things like arctan2, that would be awesome. My math background is all right, but the advanced formulas and traditional math notation are very difficult for me to translate into code.

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  • Turtle Graphics as a Haskell Monad

    - by iliis
    I'm trying to implement turtle graphis in Haskell. The goal is to be able to write a function like this: draw_something = do fordward 100 right 90 forward 100 ... and then have it produce a list of points (maybe with additional properties): > draw_something (0,0) 0 -- start at (0,0) facing east (0 degrees) [(0,0), (0,100), (-100,100), ...] I have all this working in a 'normal' way, but I fail to implement it as a Haskell Monad and use the do-notation. The basic code: data State a = State (a, a) a -- (x,y), angle deriving (Show, Eq) initstate :: State Float initstate = State (0.0,0.0) 0.0 -- constrain angles to 0 to 2*pi fmod :: Float -> Float fmod a | a >= 2*pi = fmod (a-2*pi) | a < 0 = fmod (a+2*pi) | otherwise = a forward :: Float -> State Float -> [State Float] forward d (State (x,y) angle) = [State (x + d * (sin angle), y + d * (cos angle)) angle] right :: Float -> State Float -> [State Float] right d (State pos angle) = [State pos (fmod (angle+d))] bind :: [State a] -> (State a -> [State a]) -> [State a] bind xs f = xs ++ (f (head $ reverse xs)) ret :: State a -> [State a] ret x = [x] With this I can now write > [initstate] `bind` (forward 100) `bind` (right (pi/2)) `bind` (forward 100) [State (0.0,0.0) 0.0,State (0.0,100.0) 0.0,State (0.0,100.0) 1.5707964,State (100.0,99.99999) 1.5707964] And get the expected result. However I fail to implement this as an instance of Monad. instance Monad [State] where ... results in `State' is not applied to enough type arguments Expected kind `*', but `State' has kind `* -> *' In the instance declaration for `Monad [State]' And if I wrap the list in a new object data StateList a = StateList [State a] instance Monad StateList where return x = StateList [x] I get Couldn't match type `a' with `State a' `a' is a rigid type variable bound by the type signature for return :: a -> StateList a at logo.hs:38:9 In the expression: x In the first argument of `StateList', namely `[x]' In the expression: StateList [x] I tried various other versions but I never got it to run as I'd like to. What am I doing wrong? What do I understand incorrectly?

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  • Optimize date query for large child tables: GiST or GIN?

    - by Dave Jarvis
    Problem 72 child tables, each having a year index and a station index, are defined as follows: CREATE TABLE climate.measurement_12_013 ( -- Inherited from table climate.measurement_12_013: id bigint NOT NULL DEFAULT nextval('climate.measurement_id_seq'::regclass), -- Inherited from table climate.measurement_12_013: station_id integer NOT NULL, -- Inherited from table climate.measurement_12_013: taken date NOT NULL, -- Inherited from table climate.measurement_12_013: amount numeric(8,2) NOT NULL, -- Inherited from table climate.measurement_12_013: category_id smallint NOT NULL, -- Inherited from table climate.measurement_12_013: flag character varying(1) NOT NULL DEFAULT ' '::character varying, CONSTRAINT measurement_12_013_category_id_check CHECK (category_id = 7), CONSTRAINT measurement_12_013_taken_check CHECK (date_part('month'::text, taken)::integer = 12) ) INHERITS (climate.measurement) CREATE INDEX measurement_12_013_s_idx ON climate.measurement_12_013 USING btree (station_id); CREATE INDEX measurement_12_013_y_idx ON climate.measurement_12_013 USING btree (date_part('year'::text, taken)); (Foreign key constraints to be added later.) The following query runs abysmally slow due to a full table scan: SELECT count(1) AS measurements, avg(m.amount) AS amount FROM climate.measurement m WHERE m.station_id IN ( SELECT s.id FROM climate.station s, climate.city c WHERE -- For one city ... -- c.id = 5182 AND -- Where stations are within an elevation range ... -- s.elevation BETWEEN 0 AND 3000 AND 6371.009 * SQRT( POW(RADIANS(c.latitude_decimal - s.latitude_decimal), 2) + (COS(RADIANS(c.latitude_decimal + s.latitude_decimal) / 2) * POW(RADIANS(c.longitude_decimal - s.longitude_decimal), 2)) ) <= 50 ) AND -- -- Begin extracting the data from the database. -- -- The data before 1900 is shaky; insufficient after 2009. -- extract( YEAR FROM m.taken ) BETWEEN 1900 AND 2009 AND -- Whittled down by category ... -- m.category_id = 1 AND m.taken BETWEEN -- Start date. (extract( YEAR FROM m.taken )||'-01-01')::date AND -- End date. Calculated by checking to see if the end date wraps -- into the next year. If it does, then add 1 to the current year. -- (cast(extract( YEAR FROM m.taken ) + greatest( -1 * sign( (extract( YEAR FROM m.taken )||'-12-31')::date - (extract( YEAR FROM m.taken )||'-01-01')::date ), 0 ) AS text)||'-12-31')::date GROUP BY extract( YEAR FROM m.taken ) The sluggishness comes from this part of the query: m.taken BETWEEN /* Start date. */ (extract( YEAR FROM m.taken )||'-01-01')::date AND /* End date. Calculated by checking to see if the end date wraps into the next year. If it does, then add 1 to the current year. */ (cast(extract( YEAR FROM m.taken ) + greatest( -1 * sign( (extract( YEAR FROM m.taken )||'-12-31')::date - (extract( YEAR FROM m.taken )||'-01-01')::date ), 0 ) AS text)||'-12-31')::date The HashAggregate from the plan shows a cost of 10006220141.11, which is, I suspect, on the astronomically huge side. There is a full table scan on the measurement table (itself having neither data nor indexes) being performed. The table aggregates 237 million rows from its child tables. Question What is the proper way to index the dates to avoid full table scans? Options I have considered: GIN GiST Rewrite the WHERE clause Separate year_taken, month_taken, and day_taken columns to the tables What are your thoughts? Thank you!

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  • java quaternion 3D rotation implementation

    - by MRM
    I made a method to rotate a list of points using quaternions, but all i get back as output is the same list i gave to rotate on. Maybe i did not understood corectly the math for 3d rotations or my code is not implemented the right way, could you give me a hand? This is the method i use: public static ArrayList<Float> rotation3D(ArrayList<Float> points, double angle, int x, int y, int z) { ArrayList<Float> newpoints = points; for (int i=0;i<points.size();i+=3) { float x_old = points.get(i).floatValue(); float y_old = points.get(i+1).floatValue(); float z_old = points.get(i+2).floatValue(); double[] initial = {1,0,0,0}; double[] total = new double[4]; double[] local = new double[4]; //components for local quaternion //w local[0] = Math.cos(0.5 * angle); //x local[1] = x * Math.sin(0.5 * angle); //y local[2] = y * Math.sin(0.5 * angle); //z local[3] = z * Math.sin(0.5 * angle); //components for final quaternion Q1*Q2 //w = w1w2 - x1x2 - y1y2 - z1z2 total[0] = local[0] * initial[0] - local[1] * initial[1] - local[2] * initial[2] - local[3] * initial[3]; //x = w1x2 + x1w2 + y1z2 - z1y2 total[1] = local[0] * initial[1] + local[1] * initial[0] + local[2] * initial[3] - local[3] * initial[2]; //y = w1y2 - x1z2 + y1w2 + z1x2 total[2] = local[0] * initial[2] - local[1] * initial[3] + local[2] * initial[0] + local[3] * initial[1]; //z = w1z2 + x1y2 - y1x2 + z1w2 total[3] = local[0] * initial[3] + local[1] * initial[2] - local[2] * initial[1] + local[3] * initial[0]; //new x,y,z of the 3d point using rotation matrix made from the final quaternion float x_new = (float)((1 - 2 * total[2] * total[2] - 2 * total[3] * total[3]) * x_old + (2 * total[1] * total[2] - 2 * total[0] * total[3]) * y_old + (2 * total[1] * total[3] + 2 * total[0] * total[2]) * z_old); float y_new = (float) ((2 * total[1] * total[2] + 2 * total[0] * total[3]) * x_old + (1 - 2 * total[1] * total[1] - 2 * total[3] * total[3]) * y_old + (2 * total[2] * total[3] + 2 * total[0] * total[1]) * z_old); float z_new = (float) ((2 * total[1] * total[3] - 2 * total[0] * total[2]) * x_old + (2 * total[2] * total[3] - 2 * total[0] * total[1]) * y_old + (1 - 2 * total[1] * total[1] - 2 * total[2] * total[2]) * z_old); newpoints.set(i, x_new); newpoints.set(i+1, y_new); newpoints.set(i+2, z_new); } return newpoints; } For rotation3D(points, 50, 0, 1, 0) where points is: 0.0, 0.0, -9.0; 0.0, 0.0, -11.0; 20.0, 0.0, -11.0; 20.0, 0.0, -9.0; i get back the same list.

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  • Collision point of 2 curves in a 3d-room

    - by Frank
    Hello, i am programming a small game for quite some time. We started coding a small FPS-Shooter inside of a project at school to get a bit experience using directX. I dont know why, but i couldnt stop the project and started programming at home aswell. At the moment i am trying to create some small AI. Of cause thats definatlly not easy, but thats my personal goal anyways. The topic could prolly fill multiple books hehe. I've got the walking part of my bots done so far. They walk along a scriped path. I am not working on the "aiming" of the bots. While programming that i hit on some math problem i couldnt solve yet. I hope of your input on this to help me get further. Concepts, ideas and everything else are highly appreciated. Problem: Calculate the position (D3DXVECTOR3) where the curve of the projectile (depends on gravity, speed), hit the curved of the enemys walking path (depends on speed). We assume that the enemy walks in a constant line. Known variables: float projectilSpeed = 2000 m/s //speed of the projectile per second float gravitation = 9.81 m/s^2 //of cause the gravity lol D3DXVECTOR3 targetPosition //position of the target stored in a vector (x,y,z) D3DXVECTOR3 projectilePosition //position of the projectile D3DXVECTOR3 targetSpeed //stores the change of the targets position in the last second Variabledefinition ProjectilePosition at time of collision = ProjectilePos_t TargetPosition at time of collision = TargetPos_t ProjectilePosition at time 0, now = ProjectilePos_0 TargetPosition at time 0, now = TargetPos_0 Time to impact = t Aim-angle = theta My try: Found a formular to calculate "drop" (Drop of the projectile based on the gravity) on Wikipedia: float drop = 0.5f * gravity * t * t The speed of the projectile has a horizontal and a vertical part.. Found a formular for that on wikipedia aswell: ProjectilVelocity.x = projectilSpeed * cos(theta) ProjectilVelocity.y = projectilSpeed * sin(theta) So i would assume this is true for the projectile curve: ProjectilePos_t.x = ProjectilePos_0.x + ProjectileSpeed * t ProjectilePos_t.y = ProjectilePos_0.y + ProjectileSpeed * t + 0.5f * gravity * t * t ProjectilePos_t.z = ProjectilePos_0.z + ProjectileSpeed * t The target walk with a constant speed, so we can determine his curve by this: TargetPos_t = TargetPos_0 + TargetSpeed * D3DXVECTOR3(t, t, t) Now i dont know how to continue. I have to solve it somehow to get a hold on the time to impact somehow. As a basic formular i could use: float time = distanz / projectileSpeed But that wouldnt be truly correct as it would assume a linear "Trajectory". We just find this behaivor when using a rocket. I hope i was able to explain the problem as much as possible. If there are questions left, feel free to ask me! Greets from germany, Frank

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  • Moving a unit precisely along a path in x,y coordinates

    - by Adam Eberbach
    I am playing around with a strategy game where squads move around a map. Each turn a certain amount of movement is allocated to a squad and if the squad has a destination the points are applied each turn until the destination is reached. Actual distance is used so if a squad moves one position in the x or y direction it uses one point, but moving diagonally takes ~1.4 points. The squad maintains actual position as float which is then rounded to allow drawing the position on the map. The path is described by touching the squad and dragging to the end position then lifting the pen or finger. (I'm doing this on an iPhone now but Android/Qt/Windows Mobile would work the same) As the pointer moves x, y points are recorded so that the squad gains a list of intermediate destinations on the way to the final destination. I'm finding that the destinations are not evenly spaced but can be further apart depending on the speed of the pointer movement. Following the path is important because obstacles or terrain matter in this game. I'm not trying to remake Flight Control but that's a similar mechanic. Here's what I've been doing, but it just seems too complicated (pseudocode): getDestination() { - self.nextDestination = remove_from_array(destinations) - self.gradient = delta y to destination / delta x to destination - self.angle = atan(self.gradient) - self.cosAngle = cos(self.angle) - self.sinAngle = sin(self.angle) } move() { - get movement allocation for this turn - if self.nextDestination not valid - - getNextDestination() - while(nextDestination valid) && (movement allocation remains) { - - find xStep and yStep using movement allocation and sinAngle/cosAngle calculated for current self.nextDestination - - if current position + xStep crosses the destination - - - find x movement remaining after self.nextDestination reached - - - calculate remaining direct path movement allocation (xStep remaining / cosAngle) - - - make self.position equal to self.nextDestination - - else - - - apply xStep and yStep to current position - } - round squad's float coordinates to integer screen coordinates - draw squad image on map } That's simplified of course, stuff like sign needs to be tweaked to ensure movement is in the right direction. If trig is the best way to do it then lookup tables can be used or maybe it doesn't matter on modern devices like it used to. Suggestions for a better way to do it? an update - iPhone has zero issues with trig and tracking tens of positions and tracks implemented as described above and it draws in floats anyway. The Bresenham method is more efficient, trig is more precise. If I was to use integer Bresenham I would want to multiply by ten or so to maintain a little more positional accuracy to benefit collisions/terrain detection.

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  • OpenGL Coordinate system confusion

    - by user146780
    Maybe I set up GLUT wrong. Basically I want verticies to be reletive to their size in pixels. Ex:right now if I create a hexagon, it hakes up the whole screen even though the units are 6. #include <iostream> #include <stdlib.h> //Needed for "exit" function #include <cmath> //Include OpenGL header files, so that we can use OpenGL #ifdef __APPLE__ #include <OpenGL/OpenGL.h> #include <GLUT/glut.h> #else #include <GL/glut.h> #endif using namespace std; //Called when a key is pressed void handleKeypress(unsigned char key, //The key that was pressed int x, int y) { //The current mouse coordinates switch (key) { case 27: //Escape key exit(0); //Exit the program } } //Initializes 3D rendering void initRendering() { //Makes 3D drawing work when something is in front of something else glEnable(GL_DEPTH_TEST); } //Called when the window is resized void handleResize(int w, int h) { //Tell OpenGL how to convert from coordinates to pixel values glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); //Switch to setting the camera perspective //Set the camera perspective glLoadIdentity(); //Reset the camera gluPerspective(45.0, //The camera angle (double)w / (double)h, //The width-to-height ratio 1.0, //The near z clipping coordinate 200.0); //The far z clipping coordinate } //Draws the 3D scene void drawScene() { //Clear information from last draw glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); //Reset the drawing perspective glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); glBegin(GL_POLYGON); //Begin quadrilateral coordinates //Trapezoid glColor3f(255,0,0); for(int i = 0; i < 6; ++i) { glVertex2d(sin(i/6.0*2* 3.1415), cos(i/6.0*2* 3.1415)); } glEnd(); //End quadrilateral coordinates glutSwapBuffers(); //Send the 3D scene to the screen } int main(int argc, char** argv) { //Initialize GLUT glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH); glutInitWindowSize(400, 400); //Set the window size //Create the window glutCreateWindow("Basic Shapes - videotutorialsrock.com"); initRendering(); //Initialize rendering //Set handler functions for drawing, keypresses, and window resizes glutDisplayFunc(drawScene); glutKeyboardFunc(handleKeypress); glutReshapeFunc(handleResize); glutMainLoop(); //Start the main loop. glutMainLoop doesn't return. return 0; //This line is never reached } How can I make it so that a polygon of 0,0 10,0 10,10 0,10 defines a polygon starting at the top left of the screen and is a width and height of 10 pixels? Thanks

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  • Avoiding explicit recursion in Haskell

    - by Travis Brown
    The following simple function applies a given monadic function iteratively until it hits a Nothing, at which point it returns the last non-Nothing value. It does what I need, and I understand how it works. lastJustM :: (Monad m) => (a -> m (Maybe a)) -> a -> m a lastJustM g x = g x >>= maybe (return x) (lastJustM g) As part of my self-education in Haskell I'm trying to avoid explicit recursion (or at least understand how to) whenever I can. It seems like there should be a simple non-explicitly recursive solution in this case, but I'm having trouble figuring it out. I don't want something like a monadic version of takeWhile, since it could be expensive to collect all the pre-Nothing values, and I don't care about them anyway. I checked Hoogle for the signature and nothing shows up. The m (Maybe a) bit makes me think a monad transformer might be useful here, but I don't really have the intuitions I'd need to come up with the details (yet). It's probably either embarrassingly easy to do this or embarrassingly easy to see why it can't or shouldn't be done, but this wouldn't be the first time I've used self-embarrassment as a pedagogical strategy. Background: Here's a simplified working example for context: suppose we're interested in random walks in the unit square, but we only care about points of exit. We have the following step function: randomStep :: (Floating a, Ord a, Random a) => a -> (a, a) -> State StdGen (Maybe (a, a)) randomStep s (x, y) = do (a, gen') <- randomR (0, 2 * pi) <$> get put gen' let (x', y') = (x + s * cos a, y + s * sin a) if x' < 0 || x' > 1 || y' < 0 || y' > 1 then return Nothing else return $ Just (x', y') Something like evalState (lastJustM (randomStep 0.01) (0.5, 0.5)) <$> newStdGen will give us a new data point.

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  • how to avoid clutch billiard balls?

    - by Nait87
    I'm working on the simple behaviour of billiard balls in a collision with each other. All works normal, but there was a problem when facing a few easy balls is the effect of coupling balls and they're cool with each other. Tell me how to prevent this. bool MGBilliard::CollisingBall(CCPoint curr_point, CCPoint next_point) { float dx = next_point.x - (curr_point.x + dvdt.x); float dy = next_point.y - (curr_point.y - dvdt.y); float d = dx*dx+dy*dy; return d <= BALL_RADIUS * BALL_RADIUS; } double MGBilliard::angleCollisionBalls(Ball* current, Ball* next) { double na; double dx = fabs(next->location.x - current->location.x); double dy = fabs(next->location.y - current->location.y); na = atan(fabs(dy/dx)); if(atan(fabs(current->location.y/current->location.x)) < atan(fabs(next->location.y/next->location.x))) na = current->angle - na; else if(atan(fabs(current->location.y/current->location.x)) > atan(fabs(next->location.y/next->location.x))) na = current->angle + na; return na; } for(unsigned int i = 0;i<BALL_COUNT;++i) { if(vBalls[i]->speed > 0){ vBalls[i]->speed += vBalls[i]->acceleration; float dsdt = vBalls[i]->speed*dt; dvdt.x = dsdt*cos(vBalls[i]->angle); dvdt.y = dsdt*sin(vBalls[i]->angle); vBalls[i]->location.x += dvdt.x; vBalls[i]->location.y += dvdt.y; for(unsigned int j = 1; j < BALL_COUNT; ++j) { if(i == j) continue; if(CollisingBall(vBalls[i]->spriteBall->getPosition(),vBalls[j]->spriteBall->getPosition())) { vBalls[j]->speed = 600; double angle; angle = angleCollisionBalls(vBalls[i],vBalls[j]); vBalls[i]->angle = (float)-angle; vBalls[j]->angle = (float)angle; } } } }

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  • JPA Database strcture for internationalisation

    - by IrishDubGuy
    I am trying to get a JPA implementation of a simple approach to internationalisation. I want to have a table of translated strings that I can reference in multiple fields in multiple tables. So all text occurrences in all tables will be replaced by a reference to the translated strings table. In combination with a language id, this would give a unique row in the translated strings table for that particular field. For example, consider a schema that has entities Course and Module as follows :- Course int course_id, int name, int description Module int module_id, int name The course.name, course.description and module.name are all referencing the id field of the translated strings table :- TranslatedString int id, String lang, String content That all seems simple enough. I get one table for all strings that could be internationalised and that table is used across all the other tables. How might I do this in JPA, using eclipselink 2.4? I've looked at embedded ElementCollection, ala this... JPA 2.0: Mapping a Map - it isn't exactly what i'm after cos it looks like it is relating the translated strings table to the pk of the owning table. This means I can only have one translatable string field per entity (unless I add new join columns into the translatable strings table, which defeats the point, its the opposite of what I am trying to do). I'm also not clear on how this would work across entites, presumably the id of each entity would have to use a database wide sequence to ensure uniqueness of the translatable strings table. BTW, I tried the example as laid out in that link and it didn't work for me - as soon as the entity had a localizedString map added, persisting it caused the client side to bomb but no obvious error on the server side and nothing persisted in the DB :S I been around the houses on this about 9 hours so far, I've looked at this Internationalization with Hibernate which appears to be trying to do the same thing as the link above (without the table definitions it hard to see what he achieved). Any help would be gratefully achieved at this point... Edit 1 - re AMS anwser below, I'm not sure that really addresses the issue. In his example it leaves the storing of the description text to some other process. The idea of this type of approach is that the entity object takes the text and locale and this (somehow!) ends up in the translatable strings table. In the first link I gave, the guy is attempting to do this by using an embedded map, which I feel is the right approach. His way though has two issues - one it doesn't seem to work! and two if it did work, it is storing the FK in the embedded table instead of the other way round (I think, I can't get it to run so I can't see exactly how it persists). I suspect the correct approach ends up with a map reference in place of each text that needs translating (the map being locale-content), but I can't see how to do this in a way that allows for multiple maps in one entity (without having corresponding multiple columns in the translatable strings table)...

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  • How to calculate where bullet hits

    - by lkjoel
    I have been trying to write an FPS in C/X11/OpenGL, but the issue that I have encountered is with calculating where the bullet hits. I have used a horrible technique, and it only sometimes works: pos size, p; size.x = 0.1; size.z = 0.1; // Since the game is technically top-down (but in a 3D perspective) // Positions are in X/Z, no Y float f; // Counter float d = FIRE_MAX + 1 /* Shortest Distance */, d1 /* Distance being calculated */; x = 0; // Index of object to hit for (f = 0.0; f < FIRE_MAX; f += .01) { // Go forwards p.x = player->pos.x + f * sin(toRadians(player->rot.x)); p.z = player->pos.z - f * cos(toRadians(player->rot.x)); // Get all objects that collide with the current position of the bullet short* objs = _colDetectGetObjects(p, size, objects); for (i = 0; i < MAX_OBJECTS; i++) { if (objs[i] == -1) { continue; } // Check the distance between the object and the player d1 = sqrt( pow((objects[i].pos.x - player->pos.x), 2) + pow((objects[i].pos.z - player->pos.z), 2)); // If it's closer, set it as the object to hit if (d1 < d) { x = i; d = d1; } } // If there was an object, hit it if (x > 0) { hit(&objects[x], FIRE_DAMAGE, explosions, currtime); break; } } It just works by making a for-loop and calculating any objects that might collide with where the bullet currently is. This, of course, is very slow, and sometimes doesn't even work. What would be the preferred way to calculate where the bullet hits? I have thought of making a line and seeing if any objects collide with that line, but I have no idea how to do that kind of collision detection. EDIT: I guess my question is this: How do I calculate the nearest object colliding in a line (that might not be a straight 45/90 degree angle)? Or are there any simpler methods of calculating where the bullet hits? The bullet is sort of like a laser, in the sense that gravity does not affect it (writing an old-school game, so I don't want it to be too realistic)

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  • activating the class need help.... :)

    - by asm_debuger
    this is my code... i dont anderstend way the class dont work... import java.awt.BorderLayout; import java.awt.Button; import java.awt.Color; import java.awt.GridLayout; import java.awt.Panel; public class Caldesinger { public Panel p1=new Panel(); public Button[] arr=new Button[20]; public String[] name = {"9","8","7","6","5","4","3","2","1","0","+","-","*","/",".","cos","sin","=","pow"}; public Caldesinger() { for (int i = 0; i < arr.length; i++) { this.arr[i]=new Button(""+name[i]); } } public Panel getP1() { return p1; } public void setP1(Panel p1) { this.p1 = p1; } public Button[] getArr() { return arr; } public void setArr(Button[] arr) { this.arr = arr; } public Object c() { this.p1.setLayout(new GridLayout(4,15)); for (int i = 0; i < arr.length; i++) { arr[i].setBackground(Color.LIGHT_GRAY); arr[i].setForeground(Color.orange); p1.add(arr[i]); } this.p1.setLayout(new GridLayout(4,15)); return this; } } the class desinge the applet this is the main: import java.applet.Applet; import java.awt.BorderLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class Mainapp extends Applet implements ActionListener { Caldesinger desinge=new Caldesinger (); public void init() { this.setLayout(new BorderLayout()); this.desinge.c(); } public void ActionPerformed(ActionEvent arg0) { for (int i = 0; i <20; i++) { if(arg0.getSource()== this.desinge.arr[i]); } } } way the method c does not work? the method desinge the applet

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  • How can I scale movement physics functions to frames per second (in a game engine)?

    - by Richard
    I am working on a game in Javascript (HTML5 Canvas). I implemented a simple algorithm that allows an object to follow another object with basic physics mixed in (a force vector to drive the object in the right direction, and the velocity stacks momentum, but is slowed by a constant drag force). At the moment, I set it up as a rectangle following the mouse (x, y) coordinates. Here's the code: // rectangle x, y position var x = 400; // starting x position var y = 250; // starting y position var FPS = 60; // frames per second of the screen // physics variables: var velX = 0; // initial velocity at 0 (not moving) var velY = 0; // not moving var drag = 0.92; // drag force reduces velocity by 8% per frame var force = 0.35; // overall force applied to move the rectangle var angle = 0; // angle in which to move // called every frame (at 60 frames per second): function update(){ // calculate distance between mouse and rectangle var dx = mouseX - x; var dy = mouseY - y; // calculate angle between mouse and rectangle var angle = Math.atan(dy/dx); if(dx < 0) angle += Math.PI; else if(dy < 0) angle += 2*Math.PI; // calculate the force (on or off, depending on user input) var curForce; if(keys[32]) // SPACE bar curForce = force; // if pressed, use 0.35 as force else curForce = 0; // otherwise, force is 0 // increment velocty by the force, and scaled by drag for x and y velX += curForce * Math.cos(angle); velX *= drag; velY += curForce * Math.sin(angle); velY *= drag; // update x and y by their velocities x += velX; y += velY; And that works fine at 60 frames per second. Now, the tricky part: my question is, if I change this to a different framerate (say, 30 FPS), how can I modify the force and drag values to keep the movement constant? That is, right now my rectangle (whose position is dictated by the x and y variables) moves at a maximum speed of about 4 pixels per second, and accelerates to its max speed in about 1 second. BUT, if I change the framerate, it moves slower (e.g. 30 FPS accelerates to only 2 pixels per frame). So, how can I create an equation that takes FPS (frames per second) as input, and spits out correct "drag" and "force" values that will behave the same way in real time? I know it's a heavy question, but perhaps somebody with game design experience, or knowledge of programming physics can help. Thank you for your efforts. jsFiddle: http://jsfiddle.net/BadDB

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  • Solaris 10 branded zone VM Templates for Solaris 11 on OTN

    - by jsavit
    Early this year I wrote the article Ours Goes To 11 which describes the ability to import Solaris 10 systems into a "Solaris 10 branded zone" under Oracle Solaris 11. I did this using Solaris 11 Express, and the capability remains in Solaris 11 with only slight changes. This important tool lets you painlessly inhaling a Solaris Container from Solaris 10 or entire Solaris 10 systems ("the global zone") into virtualized environments on a Solaris 11 OS. Just recently, Oracle provided Oracle VM Templates for Oracle Solaris 10 Zones to let you create Solaris 10 branded zones for Solaris 11 even if you don't currently have access to install media or a running Solaris 10 system. To use this, just download the Oracle VM Template for Oracle Solaris Zone 10 from OTN at http://www.oracle.com/technetwork/server-storage/solaris11/downloads/virtual-machines-1355605.html. This page contains images of Oracle Solaris 10 8/11 (the recent update to Solaris 10) in SPARC and x86 formats suitable for creating branded zones. The same page also has a VirtualBox image you can download for a complete Solaris 10 install in a guest virtual machine you can run on any host OS that supports VirtualBox. Both sets of downloads provide a quick - and extremely easy - way to set up a virtual Solaris 10 environment. In the case of the Oracle VM Templates, they illustrate several advanced features of Solaris 11. To start, just go to the above link, download the template for the hardware platform (SPARC or x86) you want, and download the README file also linked from that page. Install prerequisites The README file tells you to install the prerequisite Solaris 11 package that implements the Solaris 10 brand. Then you can install instances of zones with that brand. # pkg install pkg:/system/zones/brand/brand-solaris10 Packages to install: 1 Create boot environment: No Create backup boot environment: Yes DOWNLOAD PKGS FILES XFER (MB) Completed 1/1 44/44 0.4/0.4 PHASE ACTIONS Install Phase 74/74 PHASE ITEMS Package State Update Phase 1/1 Image State Update Phase 2/2 That took only a few minutes, and didn't require a reboot. Install the Solaris 10 zone Now it's time to run the downloaded template file. First make it executable via the chmod command, of course. I found that (unlike stated in the README) there was no need to rename the downloaded file to remove the .bin. When you run it you provide several parameters to describe the zone configuration: -a IP address - the IP address and optional netmask for the zone. This is the only mandatory parameter. -z zonename - the name of the zone you would like to create. -i interface - the package will create an exclusive-IP zone using a virtual NIC (vnic) based on this physical interface. In my case, I have a NIC called rge0. -p PATH - specifies the path in which you want the zoneroot to be placed. In my case, I have a ZFS dataset mounted at /zones, and this will create a zoneroot at /zones/s10u10. Kicking it off, you will see a copyright message, and then messages showing progress building the zone, which only takes a few minutes. # ./solaris-10u10-x86.bin -p /zones -a 192.168.1.100 -i rge0 -z s10u10 ... ... Checking disk-space for extraction Ok Extracting in /export/home/CDimages/s10zone/bootimage.ihaqvh ... 100% [===============================] Checking data integrity Ok Checking platform compatibility The host and the image do not have the same Solaris release: host Solaris release: 5.11 image Solaris release: 5.10 Will create a Solaris 10 branded zone. Warning: could not find a defaultrouter Zone won't have any defaultrouter configured IMAGE: ./solaris-10u10-x86.bin ZONE: s10u10 ZONEPATH: /zones/s10u10 INTERFACE: rge0 VNIC: vnicZBI13379 MAC ADDR: 2:8:20:5c:1a:cc IP ADDR: 192.168.1.100 NETMASK: 255.255.255.0 DEFROUTER: NONE TIMEZONE: US/Arizona Checking disk-space for installation Ok Installing in /zones/s10u10 ... 100% [===============================] Using a static exclusive-IP Attaching s10u10 Booting s10u10 Waiting for boot to complete booting... booting... booting... Zone s10u10 booted The zone's root password has been set using the root password of the local host. You can change the zone's root password to further harden the security of the zone: being root, log into the zone from the local host with the command 'zlogin s10u10'. Once logged in, change the root password with the command 'passwd'. The nifty part in my opinion (besides being so easy), is that the zone was created as an exclusive-IP zone on a virtual NIC. This network configuration lets you enforce traffic isolation from other zones, enforce network Quality of Service, and even let the zone set its own characteristics like IP address and packet size. Independence of the zone's network characteristics from the global zone is one of the enhancements in Solaris 10 that make it easier to consolidate zones while preserving their autonomy, yet provide control in a consolidated environment. Let's see what the virtual network environment looks like by issuing commands from the Solaris 11 global zone. First I'll use Old School ifconfig, and then I'll use the new ipadm and dladm commands. # ifconfig -a4 lo0: flags=2001000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv4,VIRTUAL> mtu 8232 index 1 inet 127.0.0.1 netmask ff000000 rge0: flags=1004943<UP,BROADCAST,RUNNING,PROMISC,MULTICAST,DHCP,IPv4> mtu 1500 index 2 inet 192.168.1.3 netmask ffffff00 broadcast 192.168.1.255 ether 0:14:d1:18:ac:bc vboxnet0: flags=201000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4,CoS> mtu 1500 index 3 inet 192.168.56.1 netmask ffffff00 broadcast 192.168.56.255 ether 8:0:27:f8:62:1c # dladm show-phys LINK MEDIA STATE SPEED DUPLEX DEVICE yge0 Ethernet unknown 0 unknown yge0 yge1 Ethernet unknown 0 unknown yge1 rge0 Ethernet up 1000 full rge0 vboxnet0 Ethernet up 1000 full vboxnet0 # dladm show-link LINK CLASS MTU STATE OVER yge0 phys 1500 unknown -- yge1 phys 1500 unknown -- rge0 phys 1500 up -- vboxnet0 phys 1500 up -- vnicZBI13379 vnic 1500 up rge0 s10u10/vnicZBI13379 vnic 1500 up rge0 s10u10/net0 vnic 1500 up rge0 # dladm show-vnic LINK OVER SPEED MACADDRESS MACADDRTYPE VID vnicZBI13379 rge0 1000 2:8:20:5c:1a:cc random 0 s10u10/vnicZBI13379 rge0 1000 2:8:20:5c:1a:cc random 0 s10u10/net0 rge0 1000 2:8:20:9d:d0:79 random 0 # ipadm show-addr ADDROBJ TYPE STATE ADDR lo0/v4 static ok 127.0.0.1/8 rge0/_a dhcp ok 192.168.1.3/24 vboxnet0/_a static ok 192.168.56.1/24 lo0/v6 static ok ::1/128 Log into the zone The install step already booted the zone, so lets log into it. Notice how you have to be appropriately privileged to log into a zone. This is my home system so I'm being a bit cavalier, but in a production environment you can give granular control of who can login to which zones. Voila! a Solaris 10 environment under a Solaris 11 kernel. Notice the output from the uname -a and ifconfig commands, and output from a ping to a nearby host. $ zlogin s10u10 zlogin: You lack sufficient privilege to run this command (all privs required) savit@home:~$ sudo zlogin s10u10 Password: [Connected to zone 's10u10' pts/5] Oracle Corporation SunOS 5.10 Generic Patch January 2005 # uname -a SunOS s10u10 5.10 Generic_Virtual i86pc i386 i86pc # ifconfig -a4 lo0: flags=2001000849 mtu 8232 index 1 inet 127.0.0.1 netmask ff000000 vnicZBI13379: flags=1000843 mtu 1500 index 2 inet 192.168.1.100 netmask ffffff00 broadcast 192.168.1.255 ether 2:8:20:5c:1a:cc # bash bash-3.2# ifconfig -a lo0: flags=2001000849 mtu 8232 index 1 inet 127.0.0.1 netmask ff000000 vnicZBI13379: flags=1000843 mtu 1500 index 2 inet 192.168.1.100 netmask ffffff00 broadcast 192.168.1.255 ether 2:8:20:5c:1a:cc bash-3.2# ping 192.168.1.2 192.168.1.2 is alive For fun, I configured Apache (setting its configuration file in /etc/apache2) and brought it up. Easy - took just a few minutes. bash-3.2# svcs apache2 STATE STIME FMRI disabled 12:38:46 svc:/network/http:apache2 bash-3.2# svcadm enable apache2 Summary In just a few minutes, I built a functioning virtual Solaris 10 environment under by Solaris 11 system. It was... easy! While I can still do it the manual way (creating and using a system archive), this is a low-effort way to create a Solaris 10 zone on Solaris 11.

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  • Transparency and AlphaBlending

    - by TechTwaddle
    In this post we'll look at the AlphaBlend() api and how it can be used for semi-transparent blitting. AlphaBlend() takes a source device context and a destination device context (DC) and combines the bits in such a way that it gives a transparent effect. Follow the links for the msdn documentation. So lets take a image like, and AlphaBlend() it on our window. The code to do so is below, (under the WM_PAINT message of WndProc) HBITMAP hBitmap=NULL, hBitmapOld=NULL; HDC hMemDC=NULL; BLENDFUNCTION bf; hdc = BeginPaint(hWnd, &ps); hMemDC = CreateCompatibleDC(hdc); hBitmap = LoadBitmap(g_hInst, MAKEINTRESOURCE(IDB_BITMAP1)); hBitmapOld = SelectObject(hMemDC, hBitmap); bf.BlendOp = AC_SRC_OVER; bf.BlendFlags = 0; bf.SourceConstantAlpha = 80; //transparency value between 0-255 bf.AlphaFormat = 0;    AlphaBlend(hdc, 0, 25, 240, 100, hMemDC, 0, 0, 240, 100, bf); SelectObject(hMemDC, hBitmapOld); DeleteDC(hMemDC); DeleteObject(hBitmap); EndPaint(hWnd, &ps);   The code above creates a memory DC (hMemDC) using CreateCompatibleDC(), loads a bitmap onto the memory DC and AlphaBlends it on the device DC (hdc), with a transparency value of 80. The result is: Pretty simple till now. Now lets try to do something a little more exciting. Lets get two images involved, each overlapping the other, giving a better demonstration of transparency. I am also going to add a few buttons so that the user can increase or decrease the transparency by clicking on the buttons. Since this is the first time I played around with GDI apis, I ran into something that everybody runs into sometime or the other, flickering. When clicking the buttons the images would flicker a lot, I figured out why and used something called double buffering to avoid flickering. We will look at both my first implementation and the second implementation just to give the concept a little more depth and perspective. A few pre-conditions before I dive into the code: - hBitmap and hBitmap2 are handles to the two images obtained using LoadBitmap(), these variables are global and are initialized under WM_CREATE - The two buttons in the application are labeled Opaque++ (make more opaque, less transparent) and Opaque-- (make less opaque, more transparent) - DrawPics(HWND hWnd, int step=0); is the function called to draw the images on the screen. This is called from under WM_PAINT and also when the buttons are clicked. When Opaque++ is clicked the 'step' value passed to DrawPics() is +20 and when Opaque-- is clicked the 'step' value is -20. The default value of 'step' is 0 Now lets take a look at my first implementation: //this funciton causes flicker, cos it draws directly to screen several times void DrawPics(HWND hWnd, int step) {     HDC hdc=NULL, hMemDC=NULL;     BLENDFUNCTION bf;     static UINT32 transparency = 100;     //no point in drawing when transparency is 0 and user clicks Opaque--     if (transparency == 0 && step < 0)         return;     //no point in drawing when transparency is 240 (opaque) and user clicks Opaque++     if (transparency == 240 && step > 0)         return;         hdc = GetDC(hWnd);     if (!hdc)         return;     //create a memory DC     hMemDC = CreateCompatibleDC(hdc);     if (!hMemDC)     {         ReleaseDC(hWnd, hdc);         return;     }     //while increasing transparency, clear the contents of screen     if (step < 0)     {         RECT rect = {0, 0, 240, 200};         FillRect(hdc, &rect, (HBRUSH)GetStockObject(WHITE_BRUSH));     }     SelectObject(hMemDC, hBitmap2);     BitBlt(hdc, 0, 25, 240, 100, hMemDC, 0, 0, SRCCOPY);         SelectObject(hMemDC, hBitmap);     transparency += step;     if (transparency >= 240)         transparency = 240;     if (transparency <= 0)         transparency = 0;     bf.BlendOp = AC_SRC_OVER;     bf.BlendFlags = 0;     bf.SourceConstantAlpha = transparency;     bf.AlphaFormat = 0;            AlphaBlend(hdc, 0, 75, 240, 100, hMemDC, 0, 0, 240, 100, bf);     DeleteDC(hMemDC);     ReleaseDC(hWnd, hdc); }   In the code above, we first get the window DC using GetDC() and create a memory DC using CreateCompatibleDC(). Then we select hBitmap2 onto the memory DC and Blt it on the window DC (hdc). Next, we select the other image, hBitmap, onto memory DC and AlphaBlend() it over window DC. As I told you before, this implementation causes flickering because it draws directly on the screen (hdc) several times. The video below shows what happens when the buttons were clicked rapidly: Well, the video recording tool I use captures only 15 frames per second and so the flickering is not visible in the video. So you're gonna have to trust me on this, it flickers (; To solve this problem we make sure that the drawing to the screen happens only once and to do that we create an additional memory DC, hTempDC. We perform all our drawing on this memory DC and finally when it is ready we Blt hTempDC on hdc, and the images are displayed in one go. Here is the code for our new DrawPics() function: //no flicker void DrawPics(HWND hWnd, int step) {     HDC hdc=NULL, hMemDC=NULL, hTempDC=NULL;     BLENDFUNCTION bf;     HBITMAP hBitmapTemp=NULL, hBitmapOld=NULL;     static UINT32 transparency = 100;     //no point in drawing when transparency is 0 and user clicks Opaque--     if (transparency == 0 && step < 0)         return;     //no point in drawing when transparency is 240 (opaque) and user clicks Opaque++     if (transparency == 240 && step > 0)         return;         hdc = GetDC(hWnd);     if (!hdc)         return;     hMemDC = CreateCompatibleDC(hdc);     hTempDC = CreateCompatibleDC(hdc);     hBitmapTemp = CreateCompatibleBitmap(hdc, 240, 150);     hBitmapOld = (HBITMAP)SelectObject(hTempDC, hBitmapTemp);     if (!hMemDC)     {         ReleaseDC(hWnd, hdc);         return;     }     //while increasing transparency, clear the contents     if (step < 0)     {         RECT rect = {0, 0, 240, 150};         FillRect(hTempDC, &rect, (HBRUSH)GetStockObject(WHITE_BRUSH));     }     SelectObject(hMemDC, hBitmap2);     //Blt hBitmap2 directly to hTempDC     BitBlt(hTempDC, 0, 0, 240, 100, hMemDC, 0, 0, SRCCOPY);         SelectObject(hMemDC, hBitmap);     transparency += step;     if (transparency >= 240)         transparency = 240;     if (transparency <= 0)         transparency = 0;     bf.BlendOp = AC_SRC_OVER;     bf.BlendFlags = 0;     bf.SourceConstantAlpha = transparency;     bf.AlphaFormat = 0;            AlphaBlend(hTempDC, 0, 50, 240, 100, hMemDC, 0, 0, 240, 100, bf);     //now hTempDC is ready, blt it directly on hdc     BitBlt(hdc, 0, 25, 240, 150, hTempDC, 0, 0, SRCCOPY);     SelectObject(hTempDC, hBitmapOld);     DeleteObject(hBitmapTemp);     DeleteDC(hMemDC);     DeleteDC(hTempDC);     ReleaseDC(hWnd, hdc); }   This function is very similar to the first version, except for the use of hTempDC. Another point to note is the use of CreateCompatibleBitmap(). When a memory device context is created using CreateCompatibleDC(), the context is exactly one monochrome pixel high and one monochrome pixel wide. So in order for us to draw anything onto hTempDC, we first have to set a bitmap on it. We use CreateCompatibleBitmap() to create a bitmap of required dimension (240x150 above), and then select this bitmap onto hTempDC. Think of it as utilizing an extra canvas, drawing everything on the canvas and finally transferring the contents to the display in one scoop. And with this version the flickering is gone, video follows:   If you want the entire solutions source code then leave a message, I will share the code over SkyDrive.

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