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fix(rt): make BuildTLAS's read barrier a memory dependency

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BuildTLAS ended with an execution-only barrier from the
acceleration-structure build to the ray-tracing and compute shader
stages. That orders the commands, but without a memory barrier the
build's writes are never made available and visible to the traceRayEXT
and rayQueryEXT reads recorded after it in the same command buffer,
which is the documented per-frame flow (BuildTLAS in onUpdate, then
RTPass): the trace may read a stale or half-written BVH.

The barrier now carries ACCELERATION_STRUCTURE_WRITE ->
ACCELERATION_STRUCTURE_READ. BuildTlasReadBarrier builds it as pure CPU
logic, so a test can check it without a GPU, as with the swapchain
barriers.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Jorijn van der Graaf 2026-10-19 03:03:16 +02:00
commit 824436e67c
Signed by: jorijnvdgraaf
GPG key ID: 2937E59CDCC1BCFB
2 changed files with 25 additions and 9 deletions
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11
implementations/Crafter.Graphics-RenderingElement3D.cpp
View file

@ -295,13 +295,6 @@ void RenderingElement3D::BuildTLAS(VkCommandBuffer cmd, std::uint32_t index, RTB
VkAccelerationStructureBuildRangeInfoKHR* tlasRangeInfoPP = &tlasRangeInfo;
Device::vkCmdBuildAccelerationStructuresKHR(cmd, 1, &tlasBuildGeometryInfo, &tlasRangeInfoPP);
vkCmdPipelineBarrier(
cmd,
VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR,
VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR | VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT,
0,
0, nullptr,
0, nullptr,
0, nullptr
);
const TlasReadBarrier readBarrier = BuildTlasReadBarrier();
vkCmdPipelineBarrier(cmd, readBarrier.srcStage, readBarrier.dstStage, 0, 1, &readBarrier.memory, 0, nullptr, 0, nullptr);
}

23
interfaces/Crafter.Graphics-RenderingElement3D.cppm
View file

@ -134,6 +134,29 @@ export namespace Crafter {
static void Add(RenderingElement3D* e);
static void Remove(RenderingElement3D* e);
};
// The dependency BuildTLAS records after its build, ordering it before
// the shaders that read the TLAS later in the same command buffer:
// traceRayEXT in a ray-tracing pass, rayQueryEXT in a compute pass. It
// has to carry the acceleration-structure memory dependency; ordering
// execution alone never makes the build's writes visible to those reads.
struct TlasReadBarrier {
VkPipelineStageFlags srcStage;
VkPipelineStageFlags dstStage;
VkMemoryBarrier memory;
};
inline TlasReadBarrier BuildTlasReadBarrier() {
return {
.srcStage = VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR,
.dstStage = VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR | VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT,
.memory = {
.sType = VK_STRUCTURE_TYPE_MEMORY_BARRIER,
.srcAccessMask = VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR,
.dstAccessMask = VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR,
},
};
}
}
#endif // !CRAFTER_GRAPHICS_WINDOW_DOM