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I've got a question regarding ComputeShader compared to PixelShader. I want to do some processing on a buffer, and this is possible both with a pixel shader and a compute shader, and now I wonder if there is any advantage in either over the other one, specifically when it comes to speed. I've had issues with either getting to use just 8 bit values, but I should be able to work-around that.

Every data point in the output will be calculated from using in total 8 data points surrounding it (MxN matrix), so I'd think this would be perfect for a pixel shader, since the different outputs don't influence each other at all.

But I was unable to find any benchmarkings to compare the shaders, and now I wonder which one I should aim for. Only target is the speed.

SinisterMJ
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From what i understand, shaders are shaders in the sense that they are just programs run by alot of threads on data. Therefore, in general there should not be any diffrence in terms of computing power/speed doing calculations in the pixel shader as opposed to the compute shader. However..

To do calculations on the pixelshader you have to massage your data so that it looks like image data, this means you have to draw a quad first of all, but also that your output must have the 'shape' of a pixel (float4 basically). This data must then be interpreted by you app into something useful

if you're using the computeshader you can completly control the number of threads to use where as for pixel shaders they have to be valid resolutions. Also you can input and output data in any format you like and take advantage of accelerated conversion using UAVs (i think)

i'd recommend using computeshaders since they are ment for doing general purpose computation and are alot easier to work with. Your over all application will probably be faster too, even if the actual shader computation time is about the same, just because you can avoid some of the hoops you have to jump through just through to get pixel shaders to do what you want.

aL3891
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    You can also usually have at least 8 output buffers so that gives you 32 bytes of possible output data per pixel. You can then just write them out as "out vec4 out0; out vec4 out1; etc...". Then you create multiple buffers and assign each to GL_COLOR_ATTACHMENT where X is buffer number. After writing to them in your shader, you can read them out by doing glReadBuffer(GL_COLOR_ATTACHMENT) followed by glReadPixels to get the data out of the specific buffer. You can see how many output buffers you can have by querying glGetIntegerv(GL_MAX_DRAW_BUFFERS, &maxDrawBuf).. – Martin Jan 02 '18 at 02:40