SPIRV-Cross/reference/shaders-msl/frag/sample-rate-frag-coord-sample-input.frag
Chip Davis fd738e3387 MSL: Adjust FragCoord for sample-rate shading.
In Metal, the `[[position]]` input to a fragment shader remains at
fragment center, even at sample rate, like OpenGL and Direct3D. In
Vulkan, however, when the fragment shader runs at sample rate, the
`FragCoord` builtin moves to the sample position in the framebuffer,
instead of the fragment center. To account for this difference, adjust
the `FragCoord`, if present, by the sample position. The -0.5 offset is
because the fragment center is at (0.5, 0.5).

Also, add an option to force sample-rate shading in a fragment shader.
Since Metal has no explicit control for this, this is done by adding a
dummy `[[sample_id]]` which is otherwise unused, if none is already
present. This is intended to be used from e.g. MoltenVK when a
pipeline's `minSampleShading` value is nonzero.

Instead of checking if any `Input` variables have `Sample`
interpolation, I've elected to check that the `SampleRateShading`
capability is present. Since `SampleId`, `SamplePosition`, and the
`Sample` interpolation decoration require this cap, this should be
equivalent for any valid SPIR-V module. If this isn't acceptable, let me
know.
2020-11-23 10:30:24 -06:00

25 lines
624 B
GLSL

#include <metal_stdlib>
#include <simd/simd.h>
using namespace metal;
struct main0_out
{
float4 FragColor [[color(0)]];
};
struct main0_in
{
float foo [[user(locn0), sample_perspective]];
};
fragment main0_out main0(main0_in in [[stage_in]], texture2d_array<float> tex [[texture(0)]], sampler texSmplr [[sampler(0)]], float4 gl_FragCoord [[position]], uint gl_SampleID [[sample_id]])
{
main0_out out = {};
gl_FragCoord.xy += get_sample_position(gl_SampleID) - 0.5;
float3 _26 = float3(gl_FragCoord.xy, in.foo);
out.FragColor = tex.sample(texSmplr, _26.xy, uint(round(_26.z)));
return out;
}