Updated meshoptimizer.

3rdparty/meshoptimizer/src/indexgenerator.cpp

@@ -6,6 +6,7 @@
 
 // This work is based on:
 // John McDonald, Mark Kilgard. Crack-Free Point-Normal Triangles using Adjacent Edge Normals. 2010
+// John Hable. Variable Rate Shading with Visibility Buffer Rendering. 2024
 namespace meshopt
 {
 
@@ -576,3 +577,99 @@ void meshopt_generateTessellationIndexBuffer(unsigned int* destination, const un
 		memcpy(destination + i * 4, patch, sizeof(patch));
 	}
 }
+
+size_t meshopt_generateProvokingIndexBuffer(unsigned int* destination, unsigned int* reorder, const unsigned int* indices, size_t index_count, size_t vertex_count)
+{
+	assert(index_count % 3 == 0);
+
+	meshopt_Allocator allocator;
+
+	unsigned int* remap = allocator.allocate<unsigned int>(vertex_count);
+	memset(remap, -1, vertex_count * sizeof(unsigned int));
+
+	// compute vertex valence; this is used to prioritize least used corner
+	// note: we use 8-bit counters for performance; for outlier vertices the valence is incorrect but that just affects the heuristic
+	unsigned char* valence = allocator.allocate<unsigned char>(vertex_count);
+	memset(valence, 0, vertex_count);
+
+	for (size_t i = 0; i < index_count; ++i)
+	{
+		unsigned int index = indices[i];
+		assert(index < vertex_count);
+
+		valence[index]++;
+	}
+
+	unsigned int reorder_offset = 0;
+
+	// assign provoking vertices; leave the rest for the next pass
+	for (size_t i = 0; i < index_count; i += 3)
+	{
+		unsigned int a = indices[i + 0], b = indices[i + 1], c = indices[i + 2];
+		assert(a < vertex_count && b < vertex_count && c < vertex_count);
+
+		// try to rotate triangle such that provoking vertex hasn't been seen before
+		// if multiple vertices are new, prioritize the one with least valence
+		// this reduces the risk that a future triangle will have all three vertices seen
+		unsigned int va = remap[a] == ~0u ? valence[a] : ~0u;
+		unsigned int vb = remap[b] == ~0u ? valence[b] : ~0u;
+		unsigned int vc = remap[c] == ~0u ? valence[c] : ~0u;
+
+		if (vb != ~0u && vb <= va && vb <= vc)
+		{
+			// abc -> bca
+			unsigned int t = a;
+			a = b, b = c, c = t;
+		}
+		else if (vc != ~0u && vc <= va && vc <= vb)
+		{
+			// abc -> cab
+			unsigned int t = c;
+			c = b, b = a, a = t;
+		}
+
+		unsigned int newidx = reorder_offset;
+
+		// now remap[a] = ~0u or all three vertices are old
+		// recording remap[a] makes it possible to remap future references to the same index, conserving space
+		if (remap[a] == ~0u)
+			remap[a] = newidx;
+
+		// we need to clone the provoking vertex to get a unique index
+		// if all three are used the choice is arbitrary since no future triangle will be able to reuse any of these
+		reorder[reorder_offset++] = a;
+
+		// note: first vertex is final, the other two will be fixed up in next pass
+		destination[i + 0] = newidx;
+		destination[i + 1] = b;
+		destination[i + 2] = c;
+
+		// update vertex valences for corner heuristic
+		valence[a]--;
+		valence[b]--;
+		valence[c]--;
+	}
+
+	// remap or clone non-provoking vertices (iterating to skip provoking vertices)
+	int step = 1;
+
+	for (size_t i = 1; i < index_count; i += step, step ^= 3)
+	{
+		unsigned int index = destination[i];
+
+		if (remap[index] == ~0u)
+		{
+			// we haven't seen the vertex before as a provoking vertex
+			// to maintain the reference to the original vertex we need to clone it
+			unsigned int newidx = reorder_offset;
+
+			remap[index] = newidx;
+			reorder[reorder_offset++] = index;
+		}
+
+		destination[i] = remap[index];
+	}
+
+	assert(reorder_offset <= vertex_count + index_count / 3);
+	return reorder_offset;
+}

3rdparty/meshoptimizer/src/meshoptimizer.h

@@ -29,7 +29,9 @@
 #endif
 
 /* Experimental APIs have unstable interface and might have implementation that's not fully tested or optimized */
+#ifndef MESHOPTIMIZER_EXPERIMENTAL
 #define MESHOPTIMIZER_EXPERIMENTAL MESHOPTIMIZER_API
+#endif
 
 /* C interface */
 #ifdef __cplusplus
@@ -137,6 +139,19 @@ MESHOPTIMIZER_API void meshopt_generateAdjacencyIndexBuffer(unsigned int* destin
  */
 MESHOPTIMIZER_API void meshopt_generateTessellationIndexBuffer(unsigned int* destination, const unsigned int* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride);
 
+/**
+ * Experimental: Generate index buffer that can be used for visibility buffer rendering and returns the size of the reorder table
+ * Each triangle's provoking vertex index is equal to primitive id; this allows passing it to the fragment shader using nointerpolate attribute.
+ * This is important for performance on hardware where primitive id can't be accessed efficiently in fragment shader.
+ * The reorder table stores the original vertex id for each vertex in the new index buffer, and should be used in the vertex shader to load vertex data.
+ * The provoking vertex is assumed to be the first vertex in the triangle; if this is not the case (OpenGL), rotate each triangle (abc -> bca) before rendering.
+ * For maximum efficiency the input index buffer should be optimized for vertex cache first.
+ *
+ * destination must contain enough space for the resulting index buffer (index_count elements)
+ * reorder must contain enough space for the worst case reorder table (vertex_count + index_count/3 elements)
+ */
+MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_generateProvokingIndexBuffer(unsigned int* destination, unsigned int* reorder, const unsigned int* indices, size_t index_count, size_t vertex_count);
+
 /**
  * Vertex transform cache optimizer
  * Reorders indices to reduce the number of GPU vertex shader invocations
@@ -340,7 +355,7 @@ enum
  * Mesh simplifier
  * Reduces the number of triangles in the mesh, attempting to preserve mesh appearance as much as possible
  * The algorithm tries to preserve mesh topology and can stop short of the target goal based on topology constraints or target error.
- * If not all attributes from the input mesh are required, it's recommended to reindex the mesh using meshopt_generateShadowIndexBuffer prior to simplification.
+ * If not all attributes from the input mesh are required, it's recommended to reindex the mesh without them prior to simplification.
  * Returns the number of indices after simplification, with destination containing new index data
  * The resulting index buffer references vertices from the original vertex buffer.
  * If the original vertex data isn't required, creating a compact vertex buffer using meshopt_optimizeVertexFetch is recommended.
@@ -360,9 +375,8 @@ MESHOPTIMIZER_API size_t meshopt_simplify(unsigned int* destination, const unsig
  *
  * vertex_attributes should have attribute_count floats for each vertex
  * attribute_weights should have attribute_count floats in total; the weights determine relative priority of attributes between each other and wrt position. The recommended weight range is [1e-3..1e-1], assuming attribute data is in [0..1] range.
- * attribute_count must be <= 16
+ * attribute_count must be <= 32
  * vertex_lock can be NULL; when it's not NULL, it should have a value for each vertex; 1 denotes vertices that can't be moved
- * TODO target_error/result_error currently use combined distance+attribute error; this may change in the future
  */
 MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_simplifyWithAttributes(unsigned int* destination, const unsigned int* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, const float* vertex_attributes, size_t vertex_attributes_stride, const float* attribute_weights, size_t attribute_count, const unsigned char* vertex_lock, size_t target_index_count, float target_error, unsigned int options, float* result_error);
 
@@ -469,6 +483,13 @@ struct meshopt_VertexFetchStatistics
  */
 MESHOPTIMIZER_API struct meshopt_VertexFetchStatistics meshopt_analyzeVertexFetch(const unsigned int* indices, size_t index_count, size_t vertex_count, size_t vertex_size);
 
+/**
+ * Meshlet is a small mesh cluster (subset) that consists of:
+ * - triangles, an 8-bit micro triangle (index) buffer, that for each triangle specifies three local vertices to use;
+ * - vertices, a 32-bit vertex indirection buffer, that for each local vertex specifies which mesh vertex to fetch vertex attributes from.
+ *
+ * For efficiency, meshlet triangles and vertices are packed into two large arrays; this structure contains offsets and counts to access the data.
+ */
 struct meshopt_Meshlet
 {
 	/* offsets within meshlet_vertices and meshlet_triangles arrays with meshlet data */
@@ -484,6 +505,7 @@ struct meshopt_Meshlet
  * Meshlet builder
  * Splits the mesh into a set of meshlets where each meshlet has a micro index buffer indexing into meshlet vertices that refer to the original vertex buffer
  * The resulting data can be used to render meshes using NVidia programmable mesh shading pipeline, or in other cluster-based renderers.
+ * When targeting mesh shading hardware, for maximum efficiency meshlets should be further optimized using meshopt_optimizeMeshlet.
  * When using buildMeshlets, vertex positions need to be provided to minimize the size of the resulting clusters.
  * When using buildMeshletsScan, for maximum efficiency the index buffer being converted has to be optimized for vertex cache first.
  *
@@ -544,7 +566,8 @@ struct meshopt_Bounds
  * Real-Time Rendering 4th Edition, section 19.3).
  *
  * vertex_positions should have float3 position in the first 12 bytes of each vertex
- * index_count/3 should be less than or equal to 512 (the function assumes clusters of limited size)
+ * vertex_count should specify the number of vertices in the entire mesh, not cluster or meshlet
+ * index_count/3 and triangle_count must not exceed implementation limits (<= 512)
  */
 MESHOPTIMIZER_API struct meshopt_Bounds meshopt_computeClusterBounds(const unsigned int* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride);
 MESHOPTIMIZER_API struct meshopt_Bounds meshopt_computeMeshletBounds(const unsigned int* meshlet_vertices, const unsigned char* meshlet_triangles, size_t triangle_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride);
@@ -642,6 +665,8 @@ inline void meshopt_generateAdjacencyIndexBuffer(T* destination, const T* indice
 template <typename T>
 inline void meshopt_generateTessellationIndexBuffer(T* destination, const T* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride);
 template <typename T>
+inline size_t meshopt_generateProvokingIndexBuffer(T* destination, unsigned int* reorder, const T* indices, size_t index_count, size_t vertex_count);
+template <typename T>
 inline void meshopt_optimizeVertexCache(T* destination, const T* indices, size_t index_count, size_t vertex_count);
 template <typename T>
 inline void meshopt_optimizeVertexCacheStrip(T* destination, const T* indices, size_t index_count, size_t vertex_count);
@@ -727,8 +752,8 @@ class meshopt_Allocator
 	typedef StorageT<void> Storage;
 
 	meshopt_Allocator()
-		: blocks()
-		, count(0)
+	    : blocks()
+	    , count(0)
 	{
 	}
 
@@ -738,7 +763,8 @@ class meshopt_Allocator
 			Storage::deallocate(blocks[i - 1]);
 	}
 
-	template <typename T> T* allocate(size_t size)
+	template <typename T>
+	T* allocate(size_t size)
 	{
 		assert(count < sizeof(blocks) / sizeof(blocks[0]));
 		T* result = static_cast<T*>(Storage::allocate(size > size_t(-1) / sizeof(T) ? size_t(-1) : size * sizeof(T)));
@@ -759,8 +785,10 @@ class meshopt_Allocator
 };
 
 // This makes sure that allocate/deallocate are lazily generated in translation units that need them and are deduplicated by the linker
-template <typename T> void* (MESHOPTIMIZER_ALLOC_CALLCONV *meshopt_Allocator::StorageT<T>::allocate)(size_t) = operator new;
-template <typename T> void (MESHOPTIMIZER_ALLOC_CALLCONV *meshopt_Allocator::StorageT<T>::deallocate)(void*) = operator delete;
+template <typename T>
+void* (MESHOPTIMIZER_ALLOC_CALLCONV *meshopt_Allocator::StorageT<T>::allocate)(size_t) = operator new;
+template <typename T>
+void (MESHOPTIMIZER_ALLOC_CALLCONV *meshopt_Allocator::StorageT<T>::deallocate)(void*) = operator delete;
 #endif
 
 /* Inline implementation for C++ templated wrappers */
@@ -875,6 +903,19 @@ inline void meshopt_generateTessellationIndexBuffer(T* destination, const T* ind
 	meshopt_generateTessellationIndexBuffer(out.data, in.data, index_count, vertex_positions, vertex_count, vertex_positions_stride);
 }
 
+template <typename T>
+inline size_t meshopt_generateProvokingIndexBuffer(T* destination, unsigned int* reorder, const T* indices, size_t index_count, size_t vertex_count)
+{
+	meshopt_IndexAdapter<T> in(NULL, indices, index_count);
+	meshopt_IndexAdapter<T> out(destination, NULL, index_count);
+
+	size_t bound = vertex_count + (index_count / 3);
+	assert(size_t(T(bound - 1)) == bound - 1); // bound - 1 must fit in T
+	(void)bound;
+
+	return meshopt_generateProvokingIndexBuffer(out.data, reorder, in.data, index_count, vertex_count);
+}
+
 template <typename T>
 inline void meshopt_optimizeVertexCache(T* destination, const T* indices, size_t index_count, size_t vertex_count)
 {