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• Fixed timestep and interpolation question

  - by Eric

  I'm following Glenn Fiedlers excellent Fix Your Timestep! tutorial to step my 2D game. The problem I'm facing is in the interpolation phase in the end. My game has a Tween-function which lets me tween properties of my game entites. Properties such as scale, shear, position, color, rotation etc. Im curious of how I'd interpolate these values, since there's a lot of them. My first thought is to keep a previous value of every property (colorPrev, scalePrev etc.), and interpolate between those. Is this the correct method? To interpolate my characters I use their velocity; renderPostion = position + (velocity * interpolation), but I cannot apply that to color for example. So what is the desired method to interpolate various properties or a entity? Is there any rule of thumb to use?

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• Glenn Fiedler's fixed timestep with fake threads

  - by kaoD

  I've implemented Glenn Fiedler's Fix Your Timestep! quite a few times in single-threaded games. Now I'm facing a different situation: I'm trying to do this in JavaScript. I know JS is single-threaded, but I plan on using requestAnimationFrame for the rendering part. This leaves me with two independent fake threads: simulation and rendering (I suppose requestAnimationFrame isn't really threaded, is it? I don't think so, it would BREAK JS.) Timing in these threads is independent too: dt for simulation and render is not the same. If I'm not mistaken, simulation should be up to Fiedler's while loop end. After the while loop, accumulator < dt so I'm left with some unspent time (dt) in the simulation thread. The problem comes in the draw/interpolation phase: const double alpha = accumulator / dt; State state = currentState*alpha + previousState * ( 1.0 - alpha ); render( state ); In my render callback, I have the current timestamp to which I can subtract the last-simulated-in-physics-timestamp to have a dt for the current frame. Should I just forget about this dt and draw using the physics thread's dt? It seems weird, since, well, I want to interpolate for the unspent time between simulation and render too, right? Of course, I want simulation and rendering to be completely independent, but I can't get around the fact that in Glenn's implementation the renderer produces time and the simulation consumes it in discrete dt sized chunks. A similar question was asked in Semi Fixed-timestep ported to javascript but the question doesn't really get to the point, and answers there point to removing physics from the render thread (which is what I'm trying to do) or just keeping physics in the render callback too (which is what I'm trying to avoid.)

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• javascript fixed timestep gameloop with requestanimation frame

  - by coffeecup

  hello i just started to read through several articles, including http://gafferongames.com/game-physics/fix-your-timestep/ ...://gamedev.stackexchange.com/questions/1589/fixed-time-step-vs-variable-time-step/ ...//dewitters.koonsolo.com/gameloop.html ...://nokarma.org/2011/02/02/javascript-game-development-the-game-loop/index.html my understanding of this is that i need the currentTime and the timeStep size and integrate all states to the next state the time which is left is then passed into the render function to do interpolation i tried to implement glenn fiedlers "the final touch", whats troubling me is that each FrameTime is about 15 (ms) and the update loop runs at about 1500 fps which seems a little bit off? heres my code this.t = 0 this.dt = 0.01 this.currTime = new Date().getTime() this.accumulator = 0.0 this.animate() animate: function(){ var newTime = new Date().getTime() , frameTime = newTime - this.currTime , alpha if ( frameTime > 0.25 ) frameTime = 0.25 this.currTime = newTime this.accumulator += frameTime while (this.accumulator >= this.dt ) { this.prev_state = this.curr_state this.update(this.t,this.dt) this.t += this.dt this.accumulator -= this.dt } alpha = this.accumulator / this.dt this.render( this.t, this.dt, alpha) requestAnimationFrame( this.animate ) } also i would like to know, are there differences between glenn fiedlers implementation and the last solution presented here ? gameloop1 gameloop2 [ sorry couldnt post more than 2 links.. ] edit : i looked into it again and adjusted the values this.currTime = new Date().getTime() this.accumulator = 0 this.p_t = 0 this.p_step = 1000/100 this.animate() animate: function(){ var newTime = new Date().getTime() , frameTime = newTime - this.currTime , alpha if(frameTime > 25) frameTime = 25 this.currTime = newTime this.accumulator += frameTime while(this.accumulator >= this.p_step){ // prevstate = currState this.update() this.p_t+=this.p_step this.accumulator -= this.p_step } alpha = this.accumulator / this.p_step this.render(alpha) requestAnimationFrame( this.animate ) now i can set the physics update rate, render runs at 60 fps and physics update at 100 fps, maybe someone could confirm this because its the first time i'm playing around with game development :-)

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• Fixed timestep with interpolation in AS3

  - by Jim Sreven

  I'm trying to implement Glenn Fiedler's popular fixed timestep system as documented here: http://gafferongames.com/game-physics/fix-your-timestep/ In Flash. I'm fairly sure that I've got it set up correctly, along with state interpolation. The result is that if my character is supposed to move at 6 pixels per frame, 35 frames per second = 210 pixels a second, it does exactly that, even if the framerate climbs or falls. The problem is it looks awful. The movement is very stuttery and just doesn't look good. I find that the amount of time in between ENTER_FRAME events, which I'm adding on to my accumulator, averages out to 28.5ms (1000/35) just as it should, but individual frame times vary wildly, sometimes an ENTER_FRAME event will come 16ms after the last, sometimes 42ms. This means that at each graphical redraw the character graphic moves by a different amount, because a different amount of time has passed since the last draw. In theory it should look smooth, but it doesn't at all. In contrast, if I just use the ultra simple system of moving the character 6px every frame, it looks completely smooth, even with these large variances in frame times. How can this be possible? I'm using getTimer() to measure these time differences, are they even reliable?

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• Semi Fixed-timestep ported to javascript

  - by abernier

  In Gaffer's "Fix Your Timestep!" article, the author explains how to free your physics' loop from the paint one. Here is the final code, written in C: double t = 0.0; const double dt = 0.01; double currentTime = hires_time_in_seconds(); double accumulator = 0.0; State previous; State current; while ( !quit ) { double newTime = time(); double frameTime = newTime - currentTime; if ( frameTime > 0.25 ) frameTime = 0.25; // note: max frame time to avoid spiral of death currentTime = newTime; accumulator += frameTime; while ( accumulator >= dt ) { previousState = currentState; integrate( currentState, t, dt ); t += dt; accumulator -= dt; } const double alpha = accumulator / dt; State state = currentState*alpha + previousState * ( 1.0 - alpha ); render( state ); } I'm trying to implement this in JavaScript but I'm quite confused about the second while loop... Here is what I have for now (simplified): ... (function animLoop(){ ... while (accumulator >= dt) { // While? In a requestAnimation loop? Maybe if? ... } ... // render requestAnimationFrame(animLoop); // stand for the 1st while loop [OK] }()) As you can see, I'm not sure about the while loop inside the requestAnimation one... I thought replacing it with a if but I'm not sure it will be equivalent... Maybe some can help me.

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• Physics timestep questions

  - by SSL

  I've got a projectile working perfectly using the code below: //initialised in loading screen 60 is the FPS - projectilEposition and velocity are Vector3 types gravity = new Vector3(0, -(float)9.81 / 60, 0); //called every frame projectilePosition += projectileVelocity; This seems to work fine but I've noticed in various projectile examples I've seen that the elapsedtime per update is taken into account. What's the difference between the two and how can I convert the above to take into account the elapsedtime? (I'm using XNA - do I use ElapsedTime.TotalSeconds or TotalMilliseconds)? Edit: Forgot to add my attempt at using elapsedtime, which seemed to break the physics: projectileVelocity.Y += -(float)((9.81 * gameTime.ElapsedGameTime.TotalSeconds * gameTime.ElapsedGameTime.TotalSeconds) * 0.5f); Thanks for the help

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• Performance due to entity update

  - by Rizzo

  I always think about 2 ways to code the global Step() function, both with pros and cons. Please note that AIStep is just to provide another more step for whoever who wants it. // Approach 1 step foreach( entity in entities ) { entity.DeltaStep( delta_time ); if( time_for_fixed_step ) entity.FixedStep(); if( time_for_AI_step ) entity.AIStep(); ... // all kind of updates you want } PRO: you just have to iterate once over all entities. CON: fidelity could be lower at some scenarios, since the entity.FixedStep() isn't going all at a time. // Approach 2 step foreach( entity in entities ) entity.DeltaStep( delta_time ); if( time_for_fixed_step ) foreach( entity in entities ) entity.FixedStep(); if( time_for_AI_step ) foreach( entity in entities ) entity.FixedStep(); // all kind of updates you want SEPARATED PRO: fidelity on FixedStep is higher, shouldn't be much time between all entities update, rather than Approach 1 where you may have to wait other updates until FixedStep() comes. CON: you iterate once for each kind of update. Also, a third approach could be a hybrid between both of them, something in the way of foreach( entity in entities ) { entity.DeltaStep( delta_time ); if( time_for_AI_step ) entity.AIStep(); // all kind of updates you want BUT FixedStep() } if( time_for_fixed_step ) { foreach( entity in entities ) { entity.FixedStep(); } } Just two loops, don't caring about time fidelity in nothing other than at FixedStep(). Any thoughts on this matter? Should it really matters to make all steps at once or am I thinking on problems that don't exist?

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• Smooth animation when using fixed time step

  - by sythical

  I'm trying to implement the game loop where the physics is independent from rendering but my animation isn't as smooth as I would like it to be and it seems to periodically jump. Here is my code: // alpha is used for interpolation double alpha = 0, counter_old_time = 0; double accumulator = 0, delta_time = 0, current_time = 0, previous_time = 0; unsigned frame_counter = 0, current_fps = 0; const unsigned physics_rate = 40, max_step_count = 5; const double step_duration = 1.0 / 40.0, accumulator_max = step_duration * 5; // information about the circ;e (position and velocity) int old_pos_x = 100, new_pos_x = 100, render_pos_x = 100, velocity_x = 60; previous_time = al_get_time(); while(true) { current_time = al_get_time(); delta_time = current_time - previous_time; previous_time = current_time; accumulator += delta_time; if(accumulator > accumulator_max) { accumulator = accumulator_max; } while(accumulator >= step_duration) { if(new_pos_x > 1330) velocity_x = -15; else if(new_pos_x < 70) velocity_x = 15; old_pos_x = new_pos_x; new_pos_x += velocity_x; accumulator -= step_duration; } alpha = accumulator / static_cast<double>(step_duration); render_pos_x = old_pos_x + (new_pos_x - old_pos_x) * alpha; al_clear_to_color(al_map_rgb(20, 20, 40)); // clears the screen al_draw_textf(font, al_map_rgb(255, 255, 255), 20, 20, 0, "current_fps: %i", current_fps); // print fps al_draw_filled_circle(render_pos_x, 400, 15, al_map_rgb(255, 255, 255)); // draw circle // I've added this to test how the program will behave when rendering takes // considerably longer than updating the game. al_rest(0.008); al_flip_display(); // swaps the buffers frame_counter++; if(al_get_time() - counter_old_time >= 1) { current_fps = frame_counter; frame_counter = 0; counter_old_time = al_get_time(); } } I have added a pause during the rendering part because I wanted to see how the code would behave when a lot of rendering is involved. Removing it makes the animation smooth but then I'll have to make sure that I don't let the frame rate drop too much and that doesn't seem like a good solution. I've been trying to fix this for a week and have had no luck so I'd be very grateful if someone can read through my code. Thank you! Edit: I added the following code to work out the actual velocity (pixels per second) of the ball each time the ball is rendered and surprisingly it's not constant so I'm guessing that's the issue. I'm not sure why it's not constant. alpha = accumulator / static_cast<double>(step_duration); render_pos_x = old_pos_x + (new_pos_x - old_pos_x) * alpha; cout << (render_pos_x - old_render_pos) / delta_time << endl; old_render_pos = render_pos_x;

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• Fixed Assets Recommended Patch Collections

  - by Cindy A B-Oracle

  After the introduction of the Recommended Patch Collections (RPCs) in late 2012, Fixed Assets development has released an RPC about every six months.  You may recall that an RPC is a collection of recommended patches consolidated into a single, downloadable patch, ready to be applied.  The RPCs are created with the following goals in mind: Stability:  Address issues that occur often and interfere with the normal completion of crucial business processes, such as period close--as observed by Oracle Development and Global Customer Support. Root Cause Fixes:  Deliver a root cause fix for data corruption issues that delay period close, normal transaction flow actions, performance, and other issues. Compact:  While bundling a large number of important corrections, the file footprint is kept as small as possible to facilitate uptake and minimize testing. Reliable:  Reliable code with multiple customer downloads and comprehensive testing by QA, Support and Proactive Support.  There has been a revision to the RPC release process for spring 2014.  Instead of releasing product-specific RPCs, development has released a 12.1.3 RPC that is EBS-wide.  This EBS RPC includes all product-recommended patches along with their dependencies. To find out more about this EBS-wide RPC, please review Oracle E-Business Suite Release 12.1.3+ Recommended Patch Collection 1 (RPC1) (Doc ID 1638535.1).

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• Enable real fixed positioning on Samsung Android browsers

  - by Mr. Shiny and New ??

  The Android browser, since 2.2, supports fixed positioning, at least under certain circumstances such as when scaling is turned off. I have a simple HTML file with no JS, but the fixed positioning on three Samsung phones I've tried is simply wrong. Instead of true fixed positioning, the header scrolls out of view then pops back into place after the scrolling is done. This doesn't happen on the Android SDK emulator for any configuration I've tested (2.2, 2.3, 2.3 x86, 4.0.4). It also doesn't happen when using the WebView in an app on the Samsung phones: in those cases the positioning works as expected. Is there a way to make the Samsung Android "stock" browser use real fixed positioning? I've tested: 1. Samsung Galaxy 551, Android 2.2 2. Samsung Galaxy S, Android 2.3 3. Samsung Galaxy S II, Android 2.3 Sample code: <html> <head> <meta name="viewport" content="initial-scale=1.0,maximum-scale=1.0,user-scalable=no,width=device-width,height=device-height"> <style> h1 { position: fixed; top: 0; left: 0; height: 32px; background-color: #CDCDCD; color: black; font-size: 32px; line-height: 32px; padding: 2px; width: 100%; margin: 0;} p { margin-top: 36px; } </style> </head> <body> <h1>Header</h1> <p>Long text goes here</p> </body> </html> The expected behaviour is that the grey header fills the top of the screen and stays put no matter how much you scroll. On Samsung Android browsers it seems to scroll out of view then pop back into place once the scrolling is done, as if the fixed-positioning is being simulated using Javascript, which it isn't. Edit Judging by the comments and "answers" it seems that maybe I wasn't clear on what I need. I am looking for a meta tag or css rule/hack or javascript toggle which turns off Samsung's broken fixed-positioning and turns on the Android browser's working fixed-positioning. I am not looking for a Javascript solution that adds broken fixed-positioning to a browser that has no support whatsoever; the Samsung fixed-positioning does that already, it just looks stupid.

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• Fixed Point to Floating Point and Backwards

  - by Ahmed Khalaf

  Is converting Fixed Pt. (fixed n bit for fraction) to IEEE double safe ? ie: does IEEE double format can represent all numbers a fixed point can represent ? The test: a number goes to floating pt format then back to it's original fixed pt format.

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• How to handle bugs that I think I fixed, but I'm not entirely sure

  - by vsz

  There are some types of bugs which are very hard to reproduce, happen very rarely and seemingly by random. It can happen, that I find a possible cause, fix it, test the program, and can't reproduce the bug. However, as it was impossible to reliably reproduce the bug and it happened so rarely, how can I indicate this in a bugtracker? What is the common way of doing it? If I set the status to fixed, and the solution to fixed, it would mean something completely fixed, wouldn't it? Is it common practice to set the status to fixed and the solution to open, to indicate to the testers, that "it's probably fixed, but needs more attention to make sure" ? Edit: most (if not all) bugtrackers have two properties for the status of a bug, maybe the names are not the same. By status I mean new, assigned, fixed, closed, etc., and by solution I mean open (new), fixed, unsolvable, not reproducible, duplicate, not a bug, etc.

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• Floating point conversion from Fixed point algorithm

  - by Viks

  Hi, I have an application which is using 24 bit fixed point calculation.I am porting it to a hardware which does support floating point, so for speed optimization I need to convert all fixed point based calculation to floating point based calculation. For this code snippet, It is calculating mantissa for(i=0;i<8207;i++) { // Do n^8/7 calculation and store // it in mantissa and exponent, scaled to // fixed point precision. } So since this calculation, does convert an integer to mantissa and exponent scaled to fixed point precision(23 bit). When I tried converting it to float, by dividing the mantissa part by precision bits and subtracting the exponent part by precision bit, it really does' t work. Please help suggesting a better way of doing it.

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• HTML + CSS: fixed background image and body width/min-width (including fiddle)

  - by insertusernamehere

  So, here is my problem. I'm kinda stuck at the moment. I have a huge background image and content in the middle with those attributes: content is centered with margin auto and has a fixed width the content is related to the image (like the image is continued within the content) this relation is only horizontally (vertically scrolling moves everything around) This works actually fine (I'm only talking desktop, not mobile here :) ) with a position fixed on the huge background image. The problem that occurs is the following: When I resize the window to "smaller than the content" the background image gets it width from the body instead of the viewport. So the relation between content and image gets lost. Now I have this little JavaScript which does the trick, but this is of course some overhead I want to avoid: $(window).resize(function(){ img.css('left', (body.width() - img.width()) / 2 ); }); This works with a fixed positioned image, but can get a litty jumpy while calculating. I also tried things like that: <div id="test" style=" position: absolute; z-index: 0; top: 0; left: 0; width: 100%: height: 100%; background: transparent url(content/dummy/brand_backgroud_1600_1.jpg) no-repeat fixed center top; "></div> But this gets me back to my problem described. Is there any "script-less", elegant solution for this problem? UPDATE: now with Fiddle The one I'm trying to solve: http://jsfiddle.net/insertusernamehere/wPmrm/ The one with Javascript that works: http://jsfiddle.net/insertusernamehere/j5E8z/ NOTE The image size is always fixed. The image never gets scaled by the browser. In the JavaScript example it get's blown. So don't care about the size.

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• C++ fixed point library?

  - by uj2

  I am looking for a free C++ fixed point library (Mainly for use with embedded devices, not for arbitrary precision math). Basically, the requirements are: No unnecessary runtime overhead: whatever can be done at compile time, should be done at compile time. Ability to transparently switch code between fixed and floating point, with no inherent overhead. Fixed point math functions. There's no much point using fixed point if you need to cast back and forth in order to take a square root. Small footprint. Any suggestions?

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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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• iOS 5 fixed positioning and virtual keyboard

  - by jeffc

  I have a mobile website which has a div pinned to the bottom of the screen via position:fixed. All works fine in iOS 5 (I'm testing on an iPod Touch) until I'm on a page with a form. When I tap into an input field and the virtual keyboard appears, suddenly the fixed position of my div is lost. The div now scrolls with the page as long as the keyboard is visible. Once I click Done to close the keyboard, the div reverts to its position at the bottom of the screen and obeys the position:fixed rule. Has anyone else experienced this sort of behavior? Is this expected? Thanks.

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• Making div fixed vertically but glued to the page's border horizontally

  - by George

  Hi! Can you please go to: http://www.binarymark.com/Products/ColorPickerPro/default.aspx and note the page's layout. What I want to do is to stick or "glue" some small div to the right side of the page, that is so that it's just outside of the right frame of the page. However, vertically I want the div to be fixed to a Window, that is no matter how much the page is scrolled, it should remain a fixed 300px from the top edge of the window. Here's what it should look like http://www.binarymark.com/layexp.png Can you help me please? Seems easy, but I have no idea how to combine vertical fixed positioning and horizontal relative/absolute positioning and making sure it supports all major browsers. Thanks.

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• Fixed positioned div with a fixed height and relative or absolute divs inside it with greater height

  - by emilolsson

  Hello I have a problem with IE. I have a fixed div like this: #fixed { position: fixed; top: 0px; left: 0px; z-index: 9998; width: 100%; height: 40px; } Inside this div I want to place another div that has a height that is higher than its holder (higher than 40px). So I put a relative or an absolute div inside it and it works splendid in all browsers except IE, at least IE8. But in IE8 the child div gets cut because of the height of 40px specified for it's holder. Is there any workaround to this problem? I'm starting to get gray hairs..

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• CSS: Horizontal, comma-separated list with fixed <li> width

  - by hello

  Hello, I would like to achieve the following structure: [gfhtfg..., kgjrfg..., asd, mrhgf, ] ^-------^ ^-------^ ^-------^ ^-------^ X X X X (X = a fixed length) I've got a <div> with a fixed length, and inside it an horizontal, comma-separated list (ul) of links. The <li> elements should have a fixed width, and so if the links exceed a fixed length an ellipsis will be shown (using the text-overflow property). I know two ways to make a list horizontal. One is using display: inline and the other using the float property. With the first approach, I can't set a fixed width because the CSS specification doesn't allow setting the width of inline elements. The second approach creates a mess :O Setting float on the <a> element, intending to limit the width there, separates it from the commas. There are no browser-compatibility issues, I only have to support WebKit. I included the code I attempted to work with: <!DOCTYPE html> <html lang="en"> <head> <title>a title</title> <style> body { font-family: arial; font-size: 10pt; } div { height: 30px; width: 300px; background: #eee; border: 1px solid #ccc; text-align: center; } ul { margin: 0px; padding: 0px; } ul li:after { content: ","; } ul li:last-child:after { content: ""; } ul li a { text-decoration: none; color: #666; } ul li { margin: 0px; padding: 0px; list-style: none; overflow: hidden; text-overflow: ellipsis; -webkit-text-overflow: ellipsis; /* Inline elements can't have a width (and they shouldn't according to the specification */ display: inline; width: 30px; } </style> </head> <body> <div> <ul> <li><a href="#">a certain link</a></li> <li><a href="#">link</a></li> <li><a href="#">once again</a></li> <li><a href="#">another one</a></li> </ul> </div> </body> </html> Thank you.

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• Timestep schemes for physics simulations

  - by ktodisco

  The operations used for stepping a physics simulation are most commonly: Integrate velocity and position Collision detection and resolution Contact resolution (in advanced cases) A while ago I came across this paper from Stanford that proposed an alternative scheme, which is as follows: Collision detection and resolution Integrate velocity Contact resolution Integrate position It's intriguing because it allows for robust solutions to the stacking problem. So it got me wondering... What, if any, alternative schemes are available, either simple or complex? What are their benefits, drawbacks, and performance considerations?

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• Will fixed-point arithmetic be worth my trouble?

  - by Thomas

  I'm working on a fluid dynamics Navier-Stokes solver that should run in real time. Hence, performance is important. Right now, I'm looking at a number of tight loops that each account for a significant fraction of the execution time: there is no single bottleneck. Most of these loops do some floating-point arithmetic, but there's a lot of branching in between. The floating-point operations are mostly limited to additions, subtractions, multiplications, divisions and comparisons. All this is done using 32-bit floats. My target platform is x86 with at least SSE1 instructions. (I've verified in the assembler output that the compiler indeed generates SSE instructions.) Most of the floating-point values that I'm working with have a reasonably small upper bound, and precision for near-zero values isn't very important. So the thought occurred to me: maybe switching to fixed-point arithmetic could speed things up? I know the only way to be really sure is to measure it, that might take days, so I'd like to know the odds of success beforehand. Fixed-point was all the rage back in the days of Doom, but I'm not sure where it stands anno 2010. Considering how much silicon is nowadays pumped into floating-point performance, is there a chance that fixed-point arithmetic will still give me a significant speed boost? Does anyone have any real-world experience that may apply to my situation?

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• Hausman Test, Fixed/random effects in SAS?

  - by John

  Hey guys, I'm trying to do a fixed effecs OLS regression, a random effects OLS Regression and a Hausman test to back up my choice for one of those models. Alas, there does not seem to be a lot of information of what the code looks like when you want to do this. I found for the Hausman test that proc model data=one out=fiml2; endogenous y1 y2; y1 = py2 * y2 + px1 * x1 + interc; y2 = py1* y1 + pz1 * z1 + d2; fit y1 y2 / ols 2sls hausman; instruments x1 z1; run; you do something like this. However, I do not have the equations in the middle, which i assume to be the fixed and random effects models? On an other site I found that PROC TSCSREG automatically displays the Hausman test, unfortunately this does not work either. When I type PROC TSCSREG data = clean; data does not become blue meaning SAS does not recognize this as a type of data input? proc tscsreg data = clean; var nof capm_erm sigma cv fvyrgro meanest tvol bmratio size ab; run; I tried this but obviously doesn't work since it does not recognize the data input, I've been searching but I can't seem to find a proper example of how the code of an hausman test looks like. On the SAS site I neither find the code one has to use to perform a fixed/random effects model. My data has 1784 observations, 578 different firms (cross section?) and spans over a 2001-2006 period in months. Any help?

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• Fixed div background

  - by Fahad

  I want to create a layout where I want to display an image to the left and content on the right. The image should stay constant when the content scrolls. The css I'm using: <style type="text/css"> html, body { margin:0; padding:0; } #page-container { margin:auto; width:900px; background-color:Black; background-image:url('images/desired_layout.png'); background-attachment: fixed; background-repeat:no-repeat; } #main-image { float:left; width:250px; height:687px; background-image:url('images/desired_layout.png'); background-attachment:fixed; background-repeat:no-repeat; } #content { margin-left:250px; background-color:Olive; height:800px; width:650px; } </style> The HTML: <div id="page-container"> <div id="main-image"></div> <div id="content"></div> </div> Alot of time on this site and I have understood that background-attachment:fixed positions the image in the entire viewport and not the element it is applied to. My question is how do I go about creating that kind of layout? I do not want to give that image as a background image, as if the window is resized, it might get hidden. I want scrollbars to appear if the window size is less than 900px( my page width) so that the image can be viewed at all times. That happens with this code, however I would like the image to start at my element instead. How do I go about doing this?? Thanks in Advance :)

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• Fixed-Function vs Shaders: Which for beginner?

  - by Rob Hays

  I'm currently going to college for computer science. Although I do plan on utilizing an existing engine at some point to create a small game, my aim right now is towards learning the fundamentals: namely, 3D programming. I've already done some research regarding the choice between DirectX and OpenGL, and the general sentiment that came out of that was that whether you choose OpenGL or DirectX as your training-wheels platform, a lot of the knowledge is transferrable to the other platform. Therefore, since OpenGL is supported by more systems (probably a silly reason to choose what to learn), I decided that I'm going to learn OpenGL first. After I made this decision to learn OpenGL, I did some more research and found out about a dichotomy that I was somewhere unaware of all this time: fixed-function OpenGL vs. modern programmable shader-based OpenGL. At first, I thought it was an obvious choice that I should choose to learn shader-based OpenGL since that's what's most commonly used in the industry today. However, I then stumbled upon the very popular Learning Modern 3D Graphics Programming by Jason L. McKesson, located here: http://www.arcsynthesis.org/gltut/ I read through the introductory bits, and in the "About This Book" section, the author states: "First, much of what is learned with this approach must be inevitably abandoned when the user encounters a graphics problem that must be solved with programmability. Programmability wipes out almost all of the fixed function pipeline, so the knowledge does not easily transfer." yet at the same time also makes the case that fixed-functionality provides an easier, more immediate learning curve for beginners by stating: "It is generally considered easiest to teach neophyte graphics programmers using the fixed function pipeline." Naturally, you can see why I might be conflicted about which paradigm to learn: Do I spend a lot of time learning (and then later unlearning) the ways of fixed-functionality, or do I choose to start out with shaders? My primary concern is that modern programmable shaders somehow require the programmer to already understand the fixed-function pipeline, but I doubt that's the case. TL;DR == As an aspiring game graphics programmer, is it in my best interest to learn 3D programming through fixed-functionality or modern shader-based programming?

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