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POOpenGLES2 iOS: How best to stream vertex animation for dynamic terrain?
 

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  1. POOpenGLES2 iOS: How best to stream vertex animation for dynamic terrain?
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    <p>I'm writing an app that creates a dynamic 640*480 terrain (changes every frame). Each terrain is stored in a raw data file which represents a string of (float) height values. So far I can read the files in sequence into memory, and dynamically create a mesh based on height values each frame (and the framerate is actually reasonable), but I am maxing out at around 20 frames before my app quits with no error or stack trace.</p> <p>I suspect that I am approaching this incorrectly. How would I stream this data so that I don't have to hold each frame in memory?</p> <p>Here is a section from my data class, which holds a collection of terrains:</p> <pre><code>- (void)addModelWithID:(int)modelID; { NSString* resourcePath = [[NSBundle mainBundle] resourcePath]; NSString* fileName = [NSString stringWithFormat:@"depth_%i.raw", modelID]; NSString* fullPath = [resourcePath stringByAppendingPathComponent:fileName]; NSData *myData = [NSData dataWithContentsOfFile:fullPath]; if (!myData) return; const float *data = [myData bytes]; int meshWidth = 640; int meshHeight = 480; Model *kModel = [[Model alloc] init]; int indicesPtr = 0; int depthPtr = 2; for (int y=0;y&lt;meshHeight;y++) // Loop through y pixels { for (int x=0;x&lt;meshWidth;x++) // Loop through x pixels { // Set up vertex positions int index = y*meshWidth+x; float xpos = ((float)x/(float)(meshWidth-1)) - 0.5f; float ypos = ((float)y/(float)(meshHeight-1)) - 0.5f; float zpos = (float)data[index]; kModel.vertices1[index*3+0] = xpos; kModel.vertices1[index*3+1] = ypos; kModel.vertices1[index*3+2] = zpos; // Create a new index based on whether the current line is even or odd (flipped horizontally if odd) int _index = (y%2==0) ? index : (y*meshWidth) + ((meshWidth-1)-x); //Create the first index kModel.indices[indicesPtr++] = _index; // Create the second index if ((x&lt;meshWidth-1) || (x==meshWidth-1 &amp;&amp; y==meshHeight-2)) kModel.indices[indicesPtr++] = _index+meshWidth; } } } // Add the model to the data object [Models addObject:kModel]; [kModel release]; } </code></pre> <p>And my draw code (each frame I call a different terrain, hopefully up to 500 or so, but I max out at ~20:</p> <pre><code>{ ... Model *kModel = [kData.kinectModels objectAtIndex:sequenceCurrentFrame]; glVertexAttribPointer(vertexHandle, 3, GL_FLOAT, GL_FALSE, 0, (const GLvoid*)kModel.vertices1); glEnableVertexAttribArray(vertexHandle); glUniformMatrix4fv(mvpMatrixHandle, 1, GL_FALSE, (const GLfloat*)&amp;modelViewProjection.data[0]); glDrawElements(GL_TRIANGLE_STRIP, kModel.numIndices, GL_UNSIGNED_SHORT, (const GLvoid*)kModel.indices); ... } </code></pre> <p>Thanks a million for your help,</p> <p>Josh</p>
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    1. USBrad Larson
    1. USJosh
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    1. COYou should definitively consider writing a vertex shader for morphing the terrain for you. Besides that, how do you release the memory of each terrain chunk?
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    2. COAs far as I understand, I can't release the memory of each terrain chunk because I need to cycle through them at ~30fps. So if I release it then I would have to load the terrain file back in each frame which would be very slow, no? Is it possible to write a vertex shader for the depth of the terrain? It does seem silly to create the x and y values every time, since they aren't changing, but I don't really know how to begin sending the Z position to the shader. Any tips?
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      1. USJosh
    3. COAn aside: use `NSData`'s `NSDataReadingMappedAlways` option (with `dataWithContentsOfFile:options:error:` as a drop-in substitution for your current `dataWithContentsOfFile:`); that'll cause the file to be memory mapped rather than loaded, so you'll get a pointer you can use exactly as if the entire file were loaded but the OS will handle what part of the file is actually in memory and what remains on disk as a caching task, automatically handling overall memory footprint.
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