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POConjugate Gradients on iPhone/iPad using OpenGL ES 2.0
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copied!<p>I wrote this as a question in a comment but I feel it is worth its own question.</p> <p>I would like to build a conjugate gradients solver on the iPhone/iPad as it would open up a realm of new possibilities for GPGPU programming on these devices such as real time optical flow/real time simulations/real time finite elements.</p> <p>The very well written chapter from <a href="http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter44.html" rel="nofollow">GpuGems</a> explains how it can be done using floating point textures.</p> <p>The first problem I have encountered is that I havent managed to create a floating point render-to-texture. Perhaps I simply dont have the right parameters for my texture setup. For example this code succeeds on the first line but then fails on the second one with an GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT error.</p> <pre><code>glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, 256, 256, 0, GL_LUMINANCE, GL_HALF_FLOAT_OES, 0); glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textureHandle, 0); </code></pre> <p>So, my question is how can I do render-to-floating-point-texture on iPhone/iPad?</p> <p>Alternatively is there another way to solve this problem? I thought one messy alternative would be to use floating point textures in a frag shader and then render the resulting 16bit half-float into a regular gl_FragColor in a fragment shader by simply storing its first 8 bits in the R and second 8 bits in the G of gl_FragColor. Then I could read these values back from the FB using glReadPixels and reinterpret them as half floats and transfer that data to a new texture and repeat the process. The obvious problem with this is that it requires a very wasteful round trip from the GPU back to the CPU and then back to the GPU and im pretty sure it wont give any speed improvement.</p> <p>Does anyone have any ideas?</p>

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