Fix upper bound for BVH8 conversion.

jbikker · Nov 25, 2024 · 067f376 · 067f376
1 parent 9e6e996
commit 067f376
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Showing 3 changed files with 10 additions and 7 deletions.
diff --git a/tiny_bvh.h b/tiny_bvh.h
@@ -84,9 +84,9 @@ THE SOFTWARE.
 #define BVHBINS 8
 
 // SAH BVH building: Heuristic parameters
-// CPU builds: C_INT = 1, C_TRAV = 0.01 seems optimal.
+// CPU builds: C_INT = 1, C_TRAV = 1 seems optimal.
 #define C_INT	1
-#define C_TRAV	0.01f
+#define C_TRAV	1
 
 // include fast AVX BVH builder
 #if defined(__x86_64__) || defined(_M_X64) || defined(__wasm_simd128__) || defined(__wasm_relaxed_simd__)
@@ -1421,7 +1421,10 @@ void BVH::Convert( const BVHLayout from, const BVHLayout to, const bool deleteOr
 	else if (from == WALD_32BYTE && to == BASIC_BVH8)
 	{
 		// allocate space
-		const unsigned spaceNeeded = usedBVHNodes;
+		// Note: The safe upper bound here is usedBVHNodes when converting an existing
+		// BVH2, but we need triCount * 2 to be safe in later conversions, e.g. to
+		// CWBVH, which may further split some leaf nodes.
+		const unsigned spaceNeeded = triCount * 2;
 		if (allocatedBVH8Nodes < spaceNeeded)
 		{
 			FATAL_ERROR_IF( bvhNode == 0, "BVH::Convert( WALD_32BYTE, BASIC_BVH8 ), bvhNode == 0." );
@@ -1486,7 +1489,7 @@ void BVH::Convert( const BVHLayout from, const BVHLayout to, const bool deleteOr
 		// Note: This can be far lower (specifically: usedBVH8Nodes) if we know that
 		// none of the BVH8 leafs has more than three primitives. 
 		// Without this guarantee, the only safe upper limit is triCount * 2, since 
-		// we will be splitting fat leafs to as we go.
+		// we will be splitting fat BVH8 leafs to as we go.
 		unsigned spaceNeeded = triCount * 2 * 5; // CWBVH nodes use 80 bytes each.
 		if (spaceNeeded > allocatedCWBVHBlocks)
 		{

diff --git a/tiny_bvh_fenster.cpp b/tiny_bvh_fenster.cpp
@@ -108,7 +108,7 @@ void Init()
 
 	// build a BVH over the scene
 #if defined(BVH_USEAVX)
-	bvh.BuildHQ( triangles, verts / 3 ); 
+	bvh.BuildHQ( triangles, verts / 3 );
 	bvh.Convert( BVH::WALD_32BYTE, BVH::BASIC_BVH8 );
 	bvh.Convert( BVH::BASIC_BVH8, BVH::CWBVH );
 #elif defined(BVH_USENEON)
@@ -133,7 +133,7 @@ void Tick( uint32_t* buf )
 	bvhvec3 right = normalize( cross( bvhvec3( 0, 1, 0 ), view ) );
 	bvhvec3 up = 0.8f * cross( view, right ), C = eye + 2 * view;
 	bvhvec3 p1 = C - right + up, p2 = C + right + up, p3 = C - right - up;
-	for( int i = 0; i < SCRWIDTH * SCRHEIGHT; i++ ) buf[i] = 0xff00ff; // purple
+	for (int i = 0; i < SCRWIDTH * SCRHEIGHT; i++) buf[i] = 0xff00ff; // purple
 
 #ifdef _WIN32
 	// on windows, we get camera controls.

diff --git a/tiny_bvh_speedtest.cpp b/tiny_bvh_speedtest.cpp
@@ -16,7 +16,7 @@
 #define BUILD_REFERENCE
 #define BUILD_AVX
 #define BUILD_NEON
-#define BUILD_SBVH
+// #define BUILD_SBVH
 #define TRAVERSE_2WAY_ST
 #define TRAVERSE_ALT2WAY_ST
 #define TRAVERSE_SOA2WAY_ST