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POWhy does OpenGL double-buffering seem to be inconsistent performance-wise?
 

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  1. POWhy does OpenGL double-buffering seem to be inconsistent performance-wise?
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    <p>I'm making a simple graphical app on OSX. I just started monitoring the frame rate by checking the difference in system time between frames. It seems to be hanging a bit every few frames.</p> <p>The app runs on an NSTimer object, currently set to 200 fps (5 ms frames). To make sure it wasn't just my main code being slow, I commented out the entire main loop, except for [self.context flushBuffer]; (and of course the frame-rate sampling code). Even repeating this single call is causing it to hang for several frames at a time. Here is an example of my console output:</p> <pre><code>4 5 6 10 5 5 5 4 6 10 5 5 5 5 5 5 20 4 5 6 20 5 5 5 </code></pre> <p>This is the time in milliseconds between each loop iteration. At 200 fps, it should be about 5 ms for each frame, but it repeatedly hangs for 10, 15, or even 20 ms. Vsyncing is disabled, as you can see in my -initOpenGL function.</p> <pre><code>-(void)initOpenGL{ NSOpenGLPixelFormatAttribute attributes[] = {NSOpenGLPFADoubleBuffer, 0}; NSOpenGLPixelFormat *pixelFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes: attributes]; self.context = [[NSOpenGLContext alloc] initWithFormat:pixelFormat shareContext:nil]; [self.context setView:[self.window contentView]]; [self.context makeCurrentContext]; //Disable Vsync int temp = 0; [self.context setValues: &amp;temp forParameter: NSOpenGLCPSwapInterval]; glViewport(0, 0, windowWidth, windowHeight); glMatrixMode(GL_PROJECTION); glOrtho(0, windowWidth, 0, windowHeight, -1, 100); //Flip all textures right side up glMatrixMode(GL_TEXTURE); glLoadIdentity(); glScalef(1.0f, -1.0f, 1.0f); glMatrixMode(GL_MODELVIEW); glEnable(GL_SCISSOR_TEST); glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); } </code></pre> <p><strong>Edit, new information: I can confirm that this has something to do with double-buffering vs single. When I initialize the NSOpenGLPixelFormat without the DoubleBuffer attribute, it runs perfectly at 200 fps. Whereas with that attribute, I continue to get the stuttering.</strong></p>
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