SPIRV-Cross/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

12 lines
227 B
GLSL

#version 450
layout(set = 0, binding = 0) uniform sampler2DArray tex;
layout(location = 0) sample in float foo;
layout(location = 0) out vec4 FragColor;
void main()
{
FragColor = texture(tex, vec3(gl_FragCoord.xy, foo));
}