On my Nvidia GeForce GTX 1050 Ti `ddxddy.shader_test` doesn't pass because of considerably different numeric results.
As Giovanni pointed out, this is because my GPU uses the fine derivate and not the coarse derivate to implement ddx() and ddy().
For this reason, the result for ddx|ddy() is quantized so that the test passes if the GPU uses either coarse or fine derivates.
Additionally, tests for both ddx_coarse|ddy_coarse() and ddx_fine|ddy_fine() are added, that expect a more precise result.
-- v3: vkd3d-shader/hlsl: Support fine derivates. vkd3d-shader/hlsl: Support coarse derivates. tests: Quantize regular and coarse derivate test results. tests: Make ddx() and ddy() test behave correctly for shader models < 4. tests: Test coarse and fine derivates.