[Migrated] Ray tracing position fetch support

[rust-gpu-bot]

Issue automatically imported from old repo: EmbarkStudios/rust-gpu#1092
Old labels: t: enhancement
Originally creatd by atynagano on 2023-09-12T05:05:37Z

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https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/HitTriangleVertexPositionsKHR.html

Is it planned, or is there any way to use such a extension?

[rust-gpu-bot]

Comment from atynagano on 2023-09-23T15:08:17Z

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    use core::arch::asm;
    use spirv_std::glam::Vec3;

    #[spirv_std::macros::gpu_only]
    pub fn get_positions() -> [Vec3; 3] {
        unsafe {
            let mut result: [Vec3; 3] = Default::default();
            asm! {
                "%f32 = OpTypeFloat 32",
                "%f32x3 = OpTypeVector %f32 3",
                // OpTypeArray in asm! is not supported yet
                // "%f32x3x3 = OpTypeArray %f32x3 3",
                "%f32x3x3 = OpTypeMatrix %f32x3 3",
                "%ptr_f32x3x3 = OpTypePointer Generic %f32x3x3",
                "%positions = OpVariable %ptr_f32x3x3 Input",
                "OpDecorate %positions BuiltIn HitTriangleVertexPositionsKHR",
                "%result = OpLoad %f32x3x3 %positions",
                "OpStore {result} %result",
                result = in(reg) &mut result,
            }
            result
        }
    }

I tried the above code and got the error message error: unknown BuiltIn HitTriangleVertexPositionsKHR. So I think rspirv needs to support it first.
(I am not familiar with spirv so this code may be wrong to begin with.)

[rust-gpu-bot]

Comment from atynagano on 2024-04-05T12:12:54Z

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Seems supported in version 0.12.