From 824436e67c181f07664fc99340191ef7911e30a9 Mon Sep 17 00:00:00 2001
From: Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>
Date: Mon, 19 Oct 2026 03:03:16 +0200
Subject: [PATCH] fix(rt): make BuildTLAS's read barrier a memory dependency

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>
---
 .../Crafter.Graphics-RenderingElement3D.cpp   | 11 ++-------
 .../Crafter.Graphics-RenderingElement3D.cppm  | 23 +++++++++++++++++++
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/implementations/Crafter.Graphics-RenderingElement3D.cpp b/implementations/Crafter.Graphics-RenderingElement3D.cpp
index 9622c94..e1754aa 100644
--- a/implementations/Crafter.Graphics-RenderingElement3D.cpp
+++ b/implementations/Crafter.Graphics-RenderingElement3D.cpp
@@ -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);
 }
\ No newline at end of file
diff --git a/interfaces/Crafter.Graphics-RenderingElement3D.cppm b/interfaces/Crafter.Graphics-RenderingElement3D.cppm
index f350aa3..dee9ebf 100644
--- a/interfaces/Crafter.Graphics-RenderingElement3D.cppm
+++ b/interfaces/Crafter.Graphics-RenderingElement3D.cppm
@@ -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