XCEngine/engine/assets/builtin/shaders/gaussian-splat-utilities.shader

Shader "Builtin Gaussian Splat Utilities"
{
    HLSLINCLUDE
    uint FloatToSortableUint(float value)
    {
        const uint rawValue = asuint(value);
        const uint mask = (rawValue & 0x80000000u) != 0u ? 0xffffffffu : 0x80000000u;
        return rawValue ^ mask;
    }
    ENDHLSL

    SubShader
    {
        Pass
        {
            Name "GaussianSplatPrepareOrder"
            HLSLPROGRAM
            #pragma target 4.5
            #pragma compute GaussianSplatPrepareOrderCS

            cbuffer PerObjectConstants
            {
                float4x4 gProjectionMatrix;
                float4x4 gViewMatrix;
                float4x4 gModelMatrix;
                float4 gCameraRight;
                float4 gCameraUp;
            };

            StructuredBuffer<float3> GaussianSplatPositions;
            RWStructuredBuffer<uint> GaussianSplatSortDistances;
            RWStructuredBuffer<uint> GaussianSplatOrderBuffer;

            [numthreads(64, 1, 1)]
            void GaussianSplatPrepareOrderCS(uint3 dispatchThreadId : SV_DispatchThreadID)
            {
                uint splatCount = 0u;
                GaussianSplatOrderBuffer.GetDimensions(splatCount);

                const uint index = dispatchThreadId.x;
                if (index >= splatCount)
                {
                    return;
                }

                GaussianSplatOrderBuffer[index] = index;

                const float3 localCenter = GaussianSplatPositions[index];
                const float3 viewCenter =
                    mul(gViewMatrix, mul(gModelMatrix, float4(localCenter, 1.0))).xyz;
                GaussianSplatSortDistances[index] = FloatToSortableUint(viewCenter.z);
            }
            ENDHLSL
        }
    }
}