ARArelius·Dec 1, 2020
> Which is what I said, you can screenshot & compare. But it becomes a fuzzy compare due to acceptable precision differences
You make it sound rigorous than it can be. A readback doesn't need to be a "screenshot" and doesn't need to be of a full scene. A frame buffer can be a 1x1 value.
Regarding precision differences, it's not much different than testing floating point math anywhere else. Shaders allow fast-math style optimizations generally, but they can be disabled at least on some platforms[1][2], otherwise one can take care in floating point math, or provide tests just using integer math.
> And it ends up being more of an integration test and not a unit test.
Sure, if you just setup scenes, render, screenshot and do a fuzzy compare, that looks more like an integration test. And I agree it's more common to see integration tests for re
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nderers. But really, it's a bit more involved in that you have to deal with uploads, command queues, readbacks, but you really can setup the infrastructure to do proper unit tests, and then you can decide how you want to handle unit testing of flexible precision code, either toggling precision in the compilers, or building your tests to properly bound your expected precision, or both.
> GPU shaders are completely different. Numbers do not have consistent behavior across differing hardware & drivers.
This is an outdated and simply not true view, every modern (PC-Spec?) GPU hardware has IEEE754 compliant floats. They have to, otherwise GPGPU wouldn't have taken off in scientific computing. compiler defaults may just not be right.
[1] https://github.com/Microsoft/DirectXShaderCompiler/blob/mast...
[2] See: #pragma optionNV(fastmath off)