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  • How to execute a Ruby file in Java, capable of calling functions from the Java program and receiving primitive-type results?

    - by Omega
    I do not fully understand what am I asking (lol!), well, in the sense of if it is even possible, that is. If it isn't, sorry. Suppose I have a Java program. It has a Main and a JavaCalculator class. JavaCalculator has some basic functions like public int sum(int a,int b) { return a + b } Now suppose I have a ruby file. Called MyProgram.rb. MyProgram.rb may contain anything you could expect from a ruby program. Let us assume it contains the following: class RubyMain def initialize print "The sum of 5 with 3 is #{sum(5,3)}" end def sum(a,b) # <---------- Something will happen here end end rubyMain = RubyMain.new Good. Now then, you might already suspect what I want to do: I want to run my Java program I want it to execute the Ruby file MyProgram.rb When the Ruby program executes, it will create an instance of JavaCalculator, execute the sum function it has, get the value, and then print it. The ruby file has been executed successfully. The Java program closes. Note: The "create an instance of JavaCalculator" is not entirely necessary. I would be satisfied with just running a sum function from, say, the Main class. My question: is such possible? Can I run a Java program which internally executes a Ruby file which is capable of commanding the Java program to do certain things and get results? In the above example, the Ruby file asks the Java program to do a sum for it and give the result. This may sound ridiculous. I am new in this kind of thing (if it is possible, that is). WHY AM I ASKING THIS? I have a Java program, which is some kind of game engine. However, my target audience is a bunch of Ruby coders. I don't want to have them learn Java at all. So I figured that perhaps the Java program could simply offer the functionality (capacity to create windows, display sprites, play sounds...) and then, my audience can simply code with Ruby the logic, which basically justs asks my Java engine to do things like displaying sprites or playing sounds. That's when I though about asking this.

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  • Avoid Postfix Increment Operator

    - by muntoo
    I've read that I should avoid the postfix increment operator because of performance reasons (in certain cases). But doesn't this affect code readability? In my opinion: for(int i = 0; i < 42; i++); /* i will never equal 42! */ Looks better than: for(int i = 0; i < 42; ++i); /* i will never equal 42! */ But this is probably just out of habit. Admittedly, I haven't seen many use ++i. Is the performance that bad to sacrifice readability, in this case? Or am I just blind, and ++i is more readable than i++?

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  • Pixel perfect collision with paths (Android)

    - by keysersoze
    Hi I'm writing a game and I'm trying to do some pixel perfect collisions with paths. The player's character has a bitmask which looks for example like this: Currenly my code that handles player's collision with path looks like this: private boolean isTerrainCollisionDetected() { if(collisionRegion.op(player.getBounds(), terrain.getBottomPathBounds(), Region.Op.INTERSECT) || collisionRegion.op(player.getBounds(), terrain.getTopPathBounds(), Region.Op.INTERSECT)) { collisionRegion.getBounds(collisionRect); for(int i = collisionRect.left; i < collisionRect.right; i++) { for(int j = collisionRect.top; j < collisionRect.bottom; j++) { if(player.getBitmask().getPixel(i - player.getX(), j - player.getY()) != Color.TRANSPARENT) { return true; } } } } return false; } The problem is that collisions aren't pixel perfect. It detects collisions in situations like this: The question is: what can I do to improve my collision detection?

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  • Isometric algorithm [fixed]

    - by David
    so i've been toying with isometric and i just cant get the tiles to be in the right order. im probably missing something obvious and i just cant see it... but even at the risk of looking stupid, heres my code. for (int i = 0; i < Tile.MapSize; i++) { for (int j = 0; j < Tile.MapSize; j++) { spriteBatch.Draw( Tile.TileSetTexture, new Rectangle( (-j * Tile.TileWidth / 2) + (i * Tile.TileWidth / 2), (i * (Tile.TileHeight - 9) / 2) - (-j * (Tile.TileHeight - 9) / 2), Tile.TileWidth, Tile.TileHeight), Tile.GetSourceRectangle(tileID), Color.White, 0.0f, new Vector2(-350, -60), SpriteEffects.None, 1.0f); } } and heres what i end up with delicious messed up map yep, bit of an issue. so if anyone could help, i'd appreciate it. edit* works now <_<

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  • How to transform mesh components?

    - by Lea Hayes
    I am attempting to transform the components of a mesh directly using a 4x4 matrix. This is working for the vertex positions, but it is not working for the normals (and probably not the tangents either). Here is what I have: // Transform vertex positions - Works like a charm! vertices = mesh.vertices; for (int i = 0; i < vertices.Length; ++i) vertices[i] = transform.MultiplyPoint(vertices[i]); // Does not work, lighting is messed up on mesh normals = mesh.normals; for (int i = 0; i < normals.Length; ++i) normals[i] = transform.MultiplyVector(normals[i]); Note: The input matrix converts from local to world space and is needed to combine multiple meshes together.

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  • Why does my program stutter so much?

    - by user36322
    I've been very frustrated trying to solve this. I've looked it up, and all the answers are the same: set IsFixedTimeStep = false. This doesn't help me at all, the program is still jittery and stutters. I have absolutely no idea what is going on, can you guys help? Code for movement (objects is a list): speed = Math.Min(speed + (speedIncrement * gameTime.ElapsedGameTime.Milliseconds / 200), maxSpeed); for (int i = objects.Count - 1; i >= 0; i--) { objects[i].rect.Y += (int)(speed * gameTime.ElapsedGameTime.Milliseconds); //Check if the object is past the screen. If it is, remove it if (objects[i].rect.Y > screenHeight) { objects.Remove(objects[i]); } }

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  • Indefinite loops where the first time is different

    - by George T
    This isn't a serious problem or anything someone has asked me to do, just a seemingly simple thing that I came up with as a mental exercise but has stumped me and which I feel that I should know the answer to already. There may be a duplicate but I didn't manage to find one. Suppose that someone asked you to write a piece of code that asks the user to enter a number and, every time the number they entered is not zero, says "Error" and asks again. When they enter zero it stops. In other words, the code keeps asking for a number and repeats until zero is entered. In each iteration except the first one it also prints "Error". The simplest way I can think of to do that would be something like the folloing pseudocode: int number = 0; do { if(number != 0) { print("Error"); } print("Enter number"); number = getInput(); }while(number != 0); While that does what it's supposed to, I personally don't like that there's repeating code (you test number != 0 twice) -something that should generally be avoided. One way to avoid this would be something like this: int number = 0; while(true) { print("Enter number"); number = getInput(); if(number == 0) { break; } else { print("Error"); } } But what I don't like in this one is "while(true)", another thing to avoid. The only other way I can think of includes one more thing to avoid: labels and gotos: int number = 0; goto question; error: print("Error"); question: print("Enter number"); number = getInput(); if(number != 0) { goto error; } Another solution would be to have an extra variable to test whether you should say "Error" or not but this is wasted memory. Is there a way to do this without doing something that's generally thought of as a bad practice (repeating code, a theoretically endless loop or the use of goto)? I understand that something like this would never be complex enough that the first way would be a problem (you'd generally call a function to validate input) but I'm curious to know if there's a way I haven't thought of.

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  • Ripping MP3s in Rhythmbox Ubuntu 12.10 (64 bit)?

    - by James Fellows Yates
    I installed a couple of days ago Ubuntu 12.10 (64 bit). I today tried ripping a CD in the MP3 format. However, whenever I try to rip, it says it is missing an extra multimedia plugin "Gstreamer extra plug-ins (i386)". I then try to install the :i386 version of the gstreamer-ugly plugins, but then I get the same problem but with the id3-demuxer (or something similar) The Terminal output I get from both problems (but replace the "MPEG-1 Layer 3 (MP3) encoder" with the "ID3-demuxer" name) is: james@clefairy:~$ rhythmbox (rhythmbox:24122): GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed Rhythmbox-Message: Missing plugin: gstreamer|0.10|rhythmbox|MPEG-1 Layer 3 (MP3) encoder|encoder-audio/mpeg, mpegversion=(int)1, layer=(int)3 /usr/lib/python2.7/dist-packages/gobject/constants.py:24: Warning: g_boxed_type_register_static: assertion `g_type_from_name (name) == 0' failed import gobject._gobject It doesn't help that each time I have to install/remove the entire Gstreamer-ugly collection each time - I can't find that specific file. The CD plays fine, it's the ripping plugin that doesn't seem to work. I didn't have this problem previously on 12.04 (64 bit).

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  • OpenGL error LNK2019

    - by Ghilliedrone
    I'm trying to compile a basic OpenGL program. I linked opengl32.lib and glu32.lib but I'm getting errors. The errors I get are: error LNK1120: 7 unresolved externals error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup error LNK2019: unresolved external symbol "public: float __thiscall GLWindow::getElapsedSeconds(void)" (?getElapsedSeconds@GLWindow@@QAEMXZ) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: bool __thiscall GLWindow::isRunning(void)" (?isRunning@GLWindow@@QAE_NXZ) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: void __thiscall GLWindow::attachExample(class Example *)" (?attachExample@GLWindow@@QAEXPAVExample@@@Z) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: void __thiscall GLWindow::destroy(void)" (?destroy@GLWindow@@QAEXXZ) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "public: __thiscall GLWindow::GLWindow(struct HINSTANCE__ *)" (??0GLWindow@@QAE@PAUHINSTANCE__@@@Z) referenced in function _WinMain@16 error LNK2019: unresolved external symbol "private: void __thiscall GLWindow::setupPixelFormat(void)" (?setupPixelFormat@GLWindow@@AAEXXZ) referenced in function "public: long __stdcall GLWindow::WndProc(struct HWND__ *,unsigned int,unsigned int,long)" (?WndProc@GLWindow@@QAGJPAUHWND__@@IIJ@Z)

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  • 2D SAT Collision Detection not working when using certain polygons (With example)

    - by sFuller
    My SAT algorithm falsely reports that collision is occurring when using certain polygons. I believe this happens when using a polygon that does not contain a right angle. Here is a simple diagram of what is going wrong: Here is the problematic code: std::vector<vec2> axesB = polygonB->GetAxes(); //loop over axes B for(int i = 0; i < axesB.size(); i++) { float minA,minB,maxA,maxB; polygonA->Project(axesB[i],&minA,&maxA); polygonB->Project(axesB[i],&minB,&maxB); float intervalDistance = polygonA->GetIntervalDistance(minA, maxA, minB, maxB); if(intervalDistance >= 0) return false; //Collision not occurring } This function retrieves axes from the polygon: std::vector<vec2> Polygon::GetAxes() { std::vector<vec2> axes; for(int i = 0; i < verts.size(); i++) { vec2 a = verts[i]; vec2 b = verts[(i+1)%verts.size()]; vec2 edge = b-a; axes.push_back(vec2(-edge.y,edge.x).GetNormailzed()); } return axes; } This function returns the normalized vector: vec2 vec2::GetNormailzed() { float mag = sqrt( x*x + y*y ); return *this/mag; } This function projects a polygon onto an axis: void Polygon::Project(vec2* axis, float* min, float* max) { float d = axis->DotProduct(&verts[0]); float _min = d; float _max = d; for(int i = 1; i < verts.size(); i++) { d = axis->DotProduct(&verts[i]); _min = std::min(_min,d); _max = std::max(_max,d); } *min = _min; *max = _max; } This function returns the dot product of the vector with another vector. float vec2::DotProduct(vec2* other) { return (x*other->x + y*other->y); } Could anyone give me a pointer in the right direction to what could be causing this bug? Edit: I forgot this function, which gives me the interval distance: float Polygon::GetIntervalDistance(float minA, float maxA, float minB, float maxB) { float intervalDistance; if (minA < minB) { intervalDistance = minB - maxA; } else { intervalDistance = minA - maxB; } return intervalDistance; //A positive value indicates this axis can be separated. } Edit 2: I have recreated the problem in HTML5/Javascript: Demo

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  • C++11 support for higher-order list functions

    - by Giorgio
    Most functional programming languages (e.g. Common Lisp, Scheme / Racket, Clojure, Haskell, Scala, Ocaml, SML) support some common higher-order functions on lists, such as map, filter, takeWhile, dropWhile, foldl, foldr (see e.g. Common Lisp, Scheme / Racket, Clojure side-by-side reference sheet, the Haskell, Scala, OCaml, and the SML documentation.) Does C++11 have equivalent standard methods or functions on lists? For example, consider the following Haskell snippet: let xs = [1, 2, 3, 4, 5] let ys = map (\x -> x * x) xs How can I express the second expression in modern standard C++? std::list<int> xs = ... // Initialize the list in some way. std::list<int> ys = ??? // How to translate the Haskell expression? What about the other higher-order functions mentioned above? Can they be directly expressed in C++?

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  • where to define variable for a for each loop?

    - by David
    can you please advise me why my first code attempt didn't work : public void listAllFiles() { for(String filename : files) { int position = 0; System.out.println(position + ": " + filename); position = position + 1; } } it kept printing position at 0 without iterating position but it seems to work after i did it this way: public void listAllFiles() { int position = 0; for(String filename : files) { System.out.println(position + ": " + filename); position = position + 1; } } I don't understand why the position + 1 was not being executed, is it because we are not meant to define variables inside for loops or am i missing something in my code.

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  • A question on nature of generated assembly in C++ and code Algebra

    - by Reetesh Mukul
    I wrote this code: #include <iostream> int main() { int a; std::cin >> a; if(a*a== 3){ std::cout << a; } return 0; } On MSVC I turned ON all optimization flags. I expected that since a*a can never be 3, so compiler should not generate code for the section: if(a*a== 3){ std::cout << a; } However it generated code for the section. I did not check GCC or LLVM/CLang. What are the limits of expectation from a C++ compiler in these scenarios?

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  • How to optimise mesh data

    - by Wardy
    So i have some procedurally generated mesh data and i want to reduce it down to its minimum number of verts. In case it matters this is a unity project. Working on the basis of a simple example, lets assume a typical flat surface of points 2 by 3. The point / vertex at [1,1] is used in many triangles. I've generated mesh for a voxel type engine that adds verts to a list based on face visiblility and now I want to remove all the duplicates. Can anyone come up with an efficient way of doing this because what i have is sooo bad its not even funny (and i don't even think it's logically correct) ... private void Optimize() { Vector3 v; Vector3 v2; for (int i = 0; i < Vertices.Count; i++) { v = Vertices[i]; for (int j = i+1; j < Vertices.Count; j++) { v2 = Vertices[j]; if (v.x == v2.x && v.y == v2.y && v.z == v2.z) { for (int ind = 0; ind < Indices.Count; ind++) { if (Indices[ind] == j) { Indices[ind] = i; } else if (Indices[ind] > j && Indices[ind] > 0) Indices[ind]--; } Vertices.RemoveAt(j); Uvs.RemoveAt(j); Normals.RemoveAt(j); } } } } EDIT: Ok i managed to get this (code sample above updated) to render an "optimised" set of verts but the UV data is all wrong now, which would make sense because i'm basically just removing any UV Vector that represents a UV coord for a removed vert and not actually considering what I need to do to "fix the tri" so to speak. The code now seemingly does work but its quite time consuming, still looking to further optimise.

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  • Make objects slide across the screen in random positions

    - by user3475907
    I want to make an object appear randomly at the right hand side of the screen and then slide across the screen and disapear at the left hand side. I am working with libgdx. I have this bit of code but it makes items fall from the top down. Please help. public EntityManager(int amount, OrthoCamera camera) { player = new Player(new Vector2(15, 230), new Vector2(0, 0), this, camera); for (int i = 0; i < amount; i++) { float x = MathUtils.random(0, MainGame.HEIGHT - TextureManager.ENEMY.getHeight()); float y = MathUtils.random(MainGame.WIDTH, MainGame.WIDTH * 10); float speed = MathUtils.random(2, 10); addEntity(new Enemy(new Vector2(x, y), new Vector2(-0, -speed))); }

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  • Simple rendering produces minor stutter

    - by Ben
    For some reason, this game loop renders the movement of a simple rectangle with no stuttering. double currTime; double prevTime = System.nanoTime() / NANO_TO_SEC; double FPSTIMER = System.nanoTime(); double maxTimeDiff = 100.0 / 1000.0; double delta = 1.0 / 60.0; int processes = 0, frames = 0; while(true){ currTime = System.nanoTime() / NANO_TO_SEC; if(currTime - prevTime > maxTimeDiff) prevTime = currTime; if(currTime >= prevTime){ process(); processes++; prevTime += delta; if(currTime < prevTime){ render(); frames++; } } else{ try{ Thread.sleep((long) (1000 * (prevTime - currTime))); } catch(Exception e){} } if(System.nanoTime() - FPSTIMER > 1000000000.0){ System.out.println("Process: " + (1000 / processes) + "ms FPS: " + (1000 / frames) + "ms"); processes = frames = 0; FPSTIMER += 1000000000.0; } } But for this game loop, I get really minor stuttering where the movement does not look smooth. long prevTime = System.currentTimeMillis(); long prevRenderTime = 0; long currRenderTime = 0; long delta = 0; long msPerTick = 1000 / 60; int frames = 0; int ticks = 0; double FPSTIMER = System.currentTimeMillis(); while (true){ long currTime = System.currentTimeMillis(); delta += (currTime - prevTime) / msPerTick; prevTime = currTime; while (delta >= 1){ ticks++; process(); delta -= 1; } prevRenderTime = System.currentTimeMillis(); render(); frames++; currRenderTime = System.currentTimeMillis(); try{ Thread.sleep((long) ((1000 / FPS) - (currRenderTime - prevRenderTime))); } catch(Exception e){} if(System.currentTimeMillis() - FPSTIMER > 1000.0){ System.out.println("Process: " + (1000.0 / ticks) + "ms FPS: " + (1000.0 / frames) + "ms"); ticks = frames = 0; FPSTIMER += 1000.0; } Is there any critical difference that I'm missing here? The one thing I noticed is that if I uncap the fps for the second game loop, the stuttering goes away. It doesn't make sense to me. Also, the second game loop came from Notch's Minicraft code with just my thread sleeping code added in.

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  • Any ideas on reducing lag in terrain generation?

    - by l5p4ngl312
    Ok so here's the deal. I've written an isometric engine that generates terrain based on camera values using 2D perlin noise. I planned on doing 3D but first I need to work out the lag issues I'm having. I will try to explain how I am doing this so that maybe someone can spot where I am going wrong. I know it should not be this laggy. There is the abstract class Block which right now just contains render(). BlockGrass, etc. extend this class and each has code in the render function to create a textured quad at the given position. Then there is the class Chunk which has the function Generate() and setBlocksInArea(). Generate uses 2D perlin noise to make a height map and stores the heights in a 2D array. It stores the positions of each block it generates in blockarray[x][y][z]. The chunks are 8x8x128. In the main game class there is a 3D array called blocksInArea. The blocks in this array are what gets rendered. When a chunk generates, it adds its blocks to this array at the correct index. It is like this so chunks can be saved to the hard drive (even though they aren't yet) but there can still be optimization with the rendering that you wouldn't have if you rendered each chunk separately. Here's where the laggy part comes in: When the camera moves to a new chunk, a row of chunks generates on the end of the axis that the camera moved on. But it still has to move the other chunks up/down in the blocksInArea (render) array. It does this by calculating the new position in the array and doing the Chunk.setBlocksInArea(): for(int x = 0; x < 8; x++){ for(int y = 0; y < 8; y++){ nx = x+(coordX - camCoordX)*8 ny = y+(coordY - camCoordY)*8 for(int z = 0; z < height[x][y]; z++){ blockarray[x][y][z] = Game.blocksInArea[nx][ny][z]; } } } My reasoning was that this would be much faster than doing the perlin noise all over again, but there are still little spikes of lag when you move in between chunks. Edit: Would it be possible to create a 3 dimensional array list so that shifting of chunks within the array would not be neccessary?

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  • SQL SERVER – Merge Two Columns into a Single Column

    - by Pinal Dave
    Here is a question which I have received from user yesterday. Hi Pinal, I want to build queries in SQL server that merge two columns of the table If I have two columns like, Column1 | Column2 1                5 2                6 3                7 4                8 I want to output like, Column1 1 2 3 4 5 6 7 8 It is a good question. Here is how we can do achieve the task. I am making the assumption that both the columns have different data and there is no duplicate. USE TempDB GO CREATE TABLE TestTable (Col1 INT, Col2 INT) GO INSERT INTO TestTable (Col1, Col2) SELECT 1, 5 UNION ALL SELECT 2, 6 UNION ALL SELECT 3, 7 UNION ALL SELECT 4, 8 GO SELECT Col1 FROM TestTable UNION SELECT Col2 FROM TestTable GO DROP TABLE TestTable GO Here is the original table. Here is the result table. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • Creating a voxel chunk with a VBO - How to translate the coordinates of each block and add it to the VBO chunk?

    - by sunsunsunsunsun
    Im trying to make a voxel engine similar to minecraft as a little learning experience and a way to learn some opengl. I have created a chunk class and I want to put all of the vertices for the whole chunk into a single VBO. I was previously only putting each block into a vbo and making a call to render each block. Anyways, I am a bit confused about how I can translate the coordinates of each block in the chunk when I'm putting all vertices into one vbo. This is what I have at the moment. public void putVertices(float tx, float ty, float tz) { float l_length = 1.0f; float l_height = 1.0f; float l_width = 1.0f; vertexPositionData.put(new float[]{ xOffset + l_length + tx, l_height + ty, zOffset + -l_width + tz, xOffset + -l_length + tx, l_height + ty, zOffset + -l_width + tz, xOffset + -l_length + tx, l_height + ty, zOffset + l_width + tz, xOffset + l_length + tx, l_height + ty, zOffset + l_width + tz, xOffset + l_length + tx, -l_height + ty, zOffset + l_width + tz, xOffset + -l_length + tx, -l_height + ty, zOffset + l_width + tz, xOffset + -l_length + tx, -l_height + ty, zOffset + -l_width + tz, xOffset + l_length + tx, -l_height + ty, zOffset + -l_width + tz, xOffset + l_length + tx, l_height + ty, zOffset + l_width + tz, xOffset + -l_length + tx, l_height + ty,zOffset + l_width + tz, xOffset + -l_length + tx, -l_height + ty,zOffset + l_width + tz, xOffset + l_length + tx, -l_height + ty, zOffset + l_width + tz, xOffset + l_length + tx, -l_height + ty, zOffset + -l_width + tz, xOffset + -l_length + tx, -l_height + ty,zOffset + -l_width + tz, xOffset + -l_length + tx, l_height + ty, zOffset + -l_width + tz, xOffset + l_length + tx, l_height + ty, zOffset + -l_width + tz, xOffset + -l_length + tx, l_height + ty, zOffset + l_width + tz, xOffset + -l_length + tx, l_height + ty, zOffset + -l_width + tz, xOffset + -l_length + tx, -l_height + ty, zOffset + -l_width + tz, xOffset + -l_length + tx, -l_height + ty,zOffset + l_width + tz, xOffset + l_length + tx, l_height + ty,zOffset + -l_width + tz, xOffset + l_length + tx, l_height + ty, zOffset + l_width + tz, xOffset + l_length + tx, -l_height + ty, zOffset + l_width + tz, xOffset + l_length + tx, -l_height + ty, zOffset + -l_width + tz }); } public void createChunk() { vertexPositionData = BufferUtils.createFloatBuffer((24*3)*activateBlocks); Random random = new Random(); for (int x = 0; x < CHUNK_SIZE; x++) { for (int y = 0; y < CHUNK_SIZE; y++) { for (int z = 0; z < CHUNK_SIZE; z++) { if(blocks[x][y][z].getActive()) { putVertices(x*2.0f, y*2.0f, z*2.0f); } } } } Whats any easy way to translate the vertices of each block into its correct position? I was previously using glTranslatef with each call to render block but this wont work now. What I am doing now also does not work, the blocks all render in stacks on top of each other and it looks like this: http://i.imgur.com/NyFtBTI.png Thanks

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  • What is upcasting/downcasting?

    - by acidzombie24
    When learning about polymorphism you commonly see something like this class Base { int prv_member; virtual void fn(){} } class Derived : Base { int more_data; virtual void fn(){} } What is upcasting or downcasting? Is (Derived*)base_ptr; an upcast or downcast? I call it upcast because you are going away from the base into something more specific. Other people told me it is a downcast because you are going down a hierarchy into something specific with the top being the root. But other people seem to call it what i call it. When converting a base ptr to a derived ptr is it called upcasting or downcasting? and if someone can link to an official source or explain why its called that than great.

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  • WHERE x = @x OR @x IS NULL

    - by steveh99999
    Every SQL DBA and developer should read the blog of MVP Erland Sommarskog – but particularly  his article on dynamic search conditions in T-SQL. I’ve linked above to his SQL 2005 article but his 2008 version is also a must-read. I seem to regularly come across uses of the SQL in the title above… Erland’s article explains in detail why this is inefficient, but I came across a nice example recently… A stored procedure contained the following code :- WHERE @Name is null or [Name] like @Name as a nonclustered index exists on the Name column, you might assume this would be handled efficiently by SQL Server. However, I got the following output from SET STATISTICS IO Table 'xxxxx'. Scan count 15, logical reads 47760, physical reads 9, read-ahead reads 13872, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Note the high number of logical reads… After a bit of investigation, we found that @Name could never actually be set to NULL in this particular example. ie the @x IS NULL was spurious… So, we changed the call to WHERE  [Name] like @Name Now, how much more efficient is this code ? Table 'xxxxx'. Scan count 3, logical reads 24, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0 A nice easy win in this case…… a full index scan has been replaced by a significantly more efficient index seek. I managed to recreate the same behaviour on Adventureworks – here’s a quick query to demonstrate :- USE adventureworks SET STATISTICS IO ON DECLARE @id INT = 51721 SELECT * FROM Sales.SalesOrderDetail WHERE @id IS NULL OR salesorderid = @id SELECT * FROM Sales.SalesOrderDetail WHERE salesorderid = @id Take a look at the STATISTICS IO output and compare the actual query plans used to prove the impact of  WHERE @id IS NULL. And just to follow some of Erland’s advice – here’s how you could get similar performance if it was possible that @id could actually sometimes contain NULL. DECLARE @sql NVARCHAR(4000), @parameterlist NVARCHAR(4000) DECLARE @id INT = 51721 – or change to NULL to prove query is functionally correct SET @sql = 'SELECT * FROM Sales.SalesOrderDetail WHERE 1 = 1' IF @id IS NOT NULL SET @sql = @sql + ' AND salesorderid = @id' IF @id IS NULL SET @sql = @sql + ' AND salesorderid IS NULL' SET @parameterlist = '@id INT' EXEC sp_executesql @sql, @parameterlist,@id Sometimes I think we focus too much on hardware and SQL Server configuration – when really the answer is focus on writing efficient SQL.

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  • why client can not receive message from server (java) [migrated]

    - by user1745931
    I have just started learning java. I modified the client side code for a server/client communication program, by creating two threads for the client side, main thread for receiving user's input, and inputThread for receiving server's response. I am sure that server has sent the response to client, however, no response message is obtain at client. Here is my code. Can anyone help me to figure it out? Thanks package clientnio; import java.net.*; import java.nio.*; import java.io.*; import java.nio.channels.*; import java.util.Scanner; public class ClientNIO { public static int bufferLen = 50; public static SocketChannel client; public static ByteBuffer writeBuffer; public static ByteBuffer readBuffer; public static void main(String[] args) { writeBuffer = ByteBuffer.allocate(bufferLen); readBuffer = ByteBuffer.allocate(bufferLen); try { SocketAddress address = new InetSocketAddress("localhost",5505); System.out.println("Local address: "+ address); client=SocketChannel.open(address); client.configureBlocking(false); //readBuffer.flip(); new inputThread(readBuffer); /* String a="asdasdasdasddffasfas"; writeBuffer.put(a.getBytes()); writeBuffer.clear(); int d=client.write(writeBuffer); writeBuffer.flip(); */ while (true) { InputStream inStream = System.in; Scanner scan = new Scanner(inStream); if (scan.hasNext()==true) { String inputLine = scan.nextLine(); writeBuffer.put(inputLine.getBytes()); //writeBuffer.clear(); System.out.println(writeBuffer.remaining()); client.write(writeBuffer); System.out.println("Sending data: "+new String(writeBuffer.array())); writeBuffer.flip(); Thread.sleep(300); } } } catch(Exception e) { System.out.println(e); } } } class inputThread extends Thread { private ByteBuffer readBuffer; public inputThread(ByteBuffer readBuffer1) { System.out.println("Receiving thread starts."); this.readBuffer = readBuffer1; start(); } @Override public void run() { try { while (true) { readBuffer.flip(); int i=ClientNIO.client.read(readBuffer); if(i>0) { byte[] b=readBuffer.array(); System.out.println("Receiving data: "+new String(b)); //client.close(); //System.out.println("Connection closed."); //break; } Thread.sleep(100); } } catch (Exception e) { System.out.println(e); } } }

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  • OpenGL ES 2 jittery camera movement

    - by user16547
    First of all, I am aware that there's no camera in OpenGL (ES 2), but from my understanding proper manipulation of the projection matrix can simulate the concept of a camera. What I'm trying to do is make my camera follow my character. My game is 2D, btw. I think the principle is the following (take Super Mario Bros or Doodle Jump as reference - actually I'm trying to replicate the mechanics of the latter): when the caracter goes beyond the center of the screen (in the positive axis/direction), update the camera to be centred on the character. Else keep the camera still. I did accomplish that, however the camera movement is noticeably jittery and I ran out of ideas how to make it smoother. First of all, my game loop (following this article): private int TICKS_PER_SECOND = 30; private int SKIP_TICKS = 1000 / TICKS_PER_SECOND; private int MAX_FRAMESKIP = 5; @Override public void run() { loops = 0; if(firstLoop) { nextGameTick = SystemClock.elapsedRealtime(); firstLoop = false; } while(SystemClock.elapsedRealtime() > nextGameTick && loops < MAX_FRAMESKIP) { step(); nextGameTick += SKIP_TICKS; loops++; } interpolation = ( SystemClock.elapsedRealtime() + SKIP_TICKS - nextGameTick ) / (float)SKIP_TICKS; draw(); } And the following code deals with moving the camera. I was unsure whether to place it in step() or draw(), but it doesn't make a difference to my problem at the moment, as I tried both and neither seemed to fix it. center just represents the y coordinate of the centre of the screen at any time. Initially it is 0. The camera object is my own custom "camera" which basically is a class that just manipulates the view and projection matrices. if(character.getVerticalSpeed() >= 0) { //only update camera if going up float[] projectionMatrix = camera.getProjectionMatrix(); if( character.getY() > center) { center += character.getVerticalSpeed(); cameraBottom = center + camera.getBottom(); cameraTop = center + camera.getTop(); Matrix.orthoM(projectionMatrix, 0, camera.getLeft(), camera.getRight(), center + camera.getBottom(), center + camera.getTop(), camera.getNear(), camera.getFar()); } } Any thought about what I should try or what I am doing wrong? Update 1: I think I updated every value you can see on screen to check whether the jittery movement is affected by that, but nothing changed, so something must be fundamentally flawed with my approach/calculations.

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  • How to implement the light trails for a tron game?

    - by Link
    Well I was creating a TRON style game, but had an issue with creating the actual light trails for the game. What I'm doing currently is I have an array the same size as my window in pixel size, implemented like this: int* collision[800][600]; Then when the bike goes on a certain pixel, it is marked with a 1 for traveled on. However what is the most efficient way to create a working light trail display? I tried to do something like this: int i, j; for(i=0; i<800; i++) for(j=0; j<600; j++) if(*collision[i][j] == 1) Image::applySurface(i, j, trailSurface, gameScreen); But it isn't working properly? It just fills the whole screen with a sprite instead. Whats a better/faster/working way to do this?

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  • Best Practice to return responses from service

    - by A9S6
    I am writing a SOAP based ASP.NET Web Service having a number of methods to deal with Client objects. e.g: int AddClient(Client c) = returns Client ID when successful List GetClients() Client GetClientInfo(int clientId) In the above methods, the return value/object for each method corresponds to the "all good" scenario i.e. A client Id will be returned if AddClient was successful or a List< of Client objects will be returned by GetClients. But what if an error occurs, how do I convey the error message to the caller? I was thinking of having a Response class: Response { StatusCode, StatusMessage, Details } where Details will hold the actual response but in that case the caller will have to cast the response every time. What are your views on the above? Is there a better solution?

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