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  1. PO
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    <p>Do I understand your code right, that you want to render a result to a texture in the first <code>if-else</code>-block and render that result to screen in the second <code>if-else</code>-block? If so, then it looks like you have a mistake in how you organize your input and output to begin with. This is what happens in your first pass (I reduced your code):</p> <pre><code>if(counter%2==0) { glBindFramebuffer(GL_FRAMEBUFFER, fboA); // will render to textureA glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textureB); // textureB is our input } else { ... } if (counter % 2 == 0) { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textureB); // textureB still as input? not textureA? } else { ... } </code></pre> <p>...and this is what happens in the second pass:</p> <pre><code>if(counter%2==0) { ... } else { glBindFramebuffer(GL_FRAMEBUFFER, fboB); // will render to textureB glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textureA); // textureA as input } if (counter % 2 == 0) { ... } else { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textureA); // textureA as input again? } </code></pre> <p>The reason why you see something in the first frame is, because you actually render your input data, but not the result of your first pass. And the reason why you have black screen in your second pass may be that your fragment shader does not work correctly. Judging from your shader code, a mistake in accessing the neighbor texels seems to be the most plausible cause for that. Can you provide the values of <code>du</code>and <code>dv</code>?</p> <p>Also I don't think that using only one texture unit should make any trouble, as Brad pointed out earlier. I'm not sure about that though.</p> <p>On a side note: for ping-ponging you should consider creating your <a href="http://www.mathematik.uni-dortmund.de/~goeddeke/gpgpu/tutorial.html#feedback2" rel="nofollow" title="Dominik Göddeke -- GPGPU::Basic Math Tutorial">FBOs as an array</a> to make your code a lot more readable.</p> <p><strong>EDIT:</strong></p> <p>I you have problems setting your uniforms <code>du</code> and <code>dv</code> with <code>glUniform1f()</code>, try <code>glUniform1i()</code> (you need to cast with <code>float()</code> in your shader then) or <code>glUniform1fv()</code> instead. I once had the same problem with the PowerVR GLES2 drivers, where this function didn't do anything and caused the uniform to be <code>0.0</code>.</p>
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    1. POPing-pong rendering between two FBOs fails after first frame.
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    1. USGood Night Nerd Pride
    1. USGood Night Nerd Pride
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      1. VTUpMod
    1. COThis might cause the first or second frames to display black, but the worst I could see happening for the frames after that would be that it would lag one frame behind what's being rendered (by drawing the input instead of the output). It's something to fix, but I'm not sure that it's what's halting his rendering here. Why I suspect the use of one texture unit is that I tried to do this myself in OpenGL ES and needed to bind the input and output textures on separate texture units for the rendering to proceed properly.
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      1. USBrad Larson
    2. COOk, this might depend on the device/driver, as I haven't experienced this so far. I still suspect a faulty fragment shader to be the real cause, though. However, you are of course correct that the mistake in ordering input and output only affects off-screen rendering. And not very much anyway.
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    3. CO@user1025555 du and dv is just a step for texture. The texture size is 256*256, so their value is 1/256, which is used to read the neighbour position.
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      1. USYongwei Xing
 

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