Merge pull request #217 from zeux/sloppy-error

simplify: Add input & output error to simplifySloppy

demo/main.cpp

@@ -471,18 +471,22 @@ void simplifySloppy(const Mesh& mesh, float threshold = 0.2f)
 	double start = timestamp();
 
 	size_t target_index_count = size_t(mesh.indices.size() * threshold);
+	float target_error = 1e-1f;
+	float result_error = 0;
 
-	lod.indices.resize(target_index_count); // note: simplifySloppy, unlike simplify, is guaranteed to output results that don't exceed the requested target_index_count
-	lod.indices.resize(meshopt_simplifySloppy(&lod.indices[0], &mesh.indices[0], mesh.indices.size(), &mesh.vertices[0].px, mesh.vertices.size(), sizeof(Vertex), target_index_count));
+	lod.indices.resize(mesh.indices.size()); // note: simplify needs space for index_count elements in the destination array, not target_index_count
+	lod.indices.resize(meshopt_simplifySloppy(&lod.indices[0], &mesh.indices[0], mesh.indices.size(), &mesh.vertices[0].px, mesh.vertices.size(), sizeof(Vertex), target_index_count, target_error, &result_error));
 
 	lod.vertices.resize(lod.indices.size() < mesh.vertices.size() ? lod.indices.size() : mesh.vertices.size()); // note: this is just to reduce the cost of resize()
 	lod.vertices.resize(meshopt_optimizeVertexFetch(&lod.vertices[0], &lod.indices[0], lod.indices.size(), &mesh.vertices[0], mesh.vertices.size(), sizeof(Vertex)));
 
 	double end = timestamp();
 
-	printf("%-9s: %d triangles => %d triangles in %.2f msec\n",
+	printf("%-9s: %d triangles => %d triangles (%.2f%% deviation) in %.2f msec\n",
 	       "SimplifyS",
-	       int(mesh.indices.size() / 3), int(lod.indices.size() / 3), (end - start) * 1000);
+	       int(mesh.indices.size() / 3), int(lod.indices.size() / 3),
+	       result_error * 100,
+	       (end - start) * 1000);
 }
 
 void simplifyPoints(const Mesh& mesh, float threshold = 0.2f)

demo/tests.cpp

@@ -740,11 +740,13 @@ static void simplifySloppyStuck()
 	const float vb[] = {0, 0, 0, 0, 0, 0, 0, 0, 0};
 	const unsigned int ib[] = {0, 1, 2, 0, 1, 2};
 
+	unsigned int* target = NULL;
+
 	// simplifying down to 0 triangles results in 0 immediately
-	assert(meshopt_simplifySloppy(0, ib, 3, vb, 3, 12, 0) == 0);
+	assert(meshopt_simplifySloppy(target, ib, 3, vb, 3, 12, 0, 0.f) == 0);
 
 	// simplifying down to 2 triangles given that all triangles are degenerate results in 0 as well
-	assert(meshopt_simplifySloppy(0, ib, 6, vb, 3, 12, 6) == 0);
+	assert(meshopt_simplifySloppy(target, ib, 6, vb, 3, 12, 6, 0.f) == 0);
 }
 
 static void simplifyPointsStuck()

gltf/mesh.cpp

@@ -515,6 +515,7 @@ static void simplifyMesh(Mesh& mesh, float threshold, bool aggressive)
 
 	size_t target_index_count = size_t(double(mesh.indices.size() / 3) * threshold) * 3;
 	float target_error = 1e-2f;
+	float target_error_aggressive = 1e-1f;
 
 	if (target_index_count < 1)
 		return;
@@ -526,10 +527,10 @@ static void simplifyMesh(Mesh& mesh, float threshold, bool aggressive)
 	// Note: if the simplifier got stuck, we can try to reindex without normals/tangents and retry
 	// For now we simply fall back to aggressive simplifier instead
 
-	// if the mesh is complex enough and the precise simplifier got "stuck", we'll try to simplify using the sloppy simplifier which is guaranteed to reach the target count
-	if (aggressive && target_index_count > 50 * 3 && mesh.indices.size() > target_index_count)
+	// if the precise simplifier got "stuck", we'll try to simplify using the sloppy simplifier; this is only used when aggressive simplification is enabled as it breaks attribute discontinuities
+	if (aggressive && mesh.indices.size() > target_index_count)
 	{
-		indices.resize(meshopt_simplifySloppy(&indices[0], &mesh.indices[0], mesh.indices.size(), positions->data[0].f, vertex_count, sizeof(Attr), target_index_count));
+		indices.resize(meshopt_simplifySloppy(&indices[0], &mesh.indices[0], mesh.indices.size(), positions->data[0].f, vertex_count, sizeof(Attr), target_index_count, target_error_aggressive));
 		mesh.indices.swap(indices);
 	}
 }

src/meshoptimizer.h

@@ -262,7 +262,7 @@ MESHOPTIMIZER_EXPERIMENTAL void meshopt_decodeFilterExp(void* buffer, size_t ver
  * 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.
  *
- * destination must contain enough space for the *source* index buffer (since optimization is iterative, this means index_count elements - *not* target_index_count!)
+ * destination must contain enough space for the target index buffer, worst case is index_count elements (*not* target_index_count)!
  * vertex_positions should have float3 position in the first 12 bytes of each vertex - similar to glVertexPointer
  * target_error represents the error relative to mesh extents that can be tolerated, e.g. 0.01 = 1% deformation
  * result_error can be NULL; when it's not NULL, it will contain the resulting (relative) error after simplification
@@ -272,15 +272,17 @@ MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_simplify(unsigned int* destination, co
 /**
  * Experimental: Mesh simplifier (sloppy)
  * Reduces the number of triangles in the mesh, sacrificing mesh apperance for simplification performance
- * The algorithm doesn't preserve mesh topology but is always able to reach target triangle count.
+ * The algorithm doesn't preserve mesh topology but can stop short of the target goal based on target error.
  * 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.
  *
- * destination must contain enough space for the target index buffer
+ * destination must contain enough space for the target index buffer, worst case is index_count elements (*not* target_index_count)!
  * vertex_positions should have float3 position in the first 12 bytes of each vertex - similar to glVertexPointer
+ * target_error represents the error relative to mesh extents that can be tolerated, e.g. 0.01 = 1% deformation
+ * result_error can be NULL; when it's not NULL, it will contain the resulting (relative) error after simplification
  */
-MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count);
+MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count, float target_error, float* result_error);
 
 /**
  * Experimental: Point cloud simplifier
@@ -289,7 +291,7 @@ MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_simplifySloppy(unsigned int* destinati
  * 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.
  *
- * destination must contain enough space for the target index buffer
+ * destination must contain enough space for the target index buffer (target_vertex_count elements)
  * vertex_positions should have float3 position in the first 12 bytes of each vertex - similar to glVertexPointer
  */
 MESHOPTIMIZER_EXPERIMENTAL size_t meshopt_simplifyPoints(unsigned int* destination, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_vertex_count);
@@ -533,7 +535,7 @@ inline int meshopt_decodeIndexSequence(T* destination, size_t index_count, const
 template <typename T>
 inline size_t meshopt_simplify(T* destination, const T* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count, float target_error, float* result_error = 0);
 template <typename T>
-inline size_t meshopt_simplifySloppy(T* destination, const T* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count);
+inline size_t meshopt_simplifySloppy(T* destination, const T* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count, float target_error, float* result_error = 0);
 template <typename T>
 inline size_t meshopt_stripify(T* destination, const T* indices, size_t index_count, size_t vertex_count, T restart_index);
 template <typename T>
@@ -855,12 +857,12 @@ inline size_t meshopt_simplify(T* destination, const T* indices, size_t index_co
 }
 
 template <typename T>
-inline size_t meshopt_simplifySloppy(T* destination, const T* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count)
+inline size_t meshopt_simplifySloppy(T* destination, const T* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count, float target_error, float* result_error)
 {
 	meshopt_IndexAdapter<T> in(0, indices, index_count);
-	meshopt_IndexAdapter<T> out(destination, 0, target_index_count);
+	meshopt_IndexAdapter<T> out(destination, 0, index_count);
 
-	return meshopt_simplifySloppy(out.data, in.data, index_count, vertex_positions, vertex_count, vertex_positions_stride, target_index_count);
+	return meshopt_simplifySloppy(out.data, in.data, index_count, vertex_positions, vertex_count, vertex_positions_stride, target_index_count, target_error, result_error);
 }
 
 template <typename T>

src/simplifier.cpp

@@ -1400,7 +1400,7 @@ size_t meshopt_simplify(unsigned int* destination, const unsigned int* indices,
 	return result_count;
 }
 
-size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* indices, size_t index_count, const float* vertex_positions_data, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count)
+size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* indices, size_t index_count, const float* vertex_positions_data, size_t vertex_count, size_t vertex_positions_stride, size_t target_index_count, float target_error, float* out_result_error)
 {
 	using namespace meshopt;
 
@@ -1412,9 +1412,6 @@ size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* ind
 	// we expect to get ~2 triangles/vertex in the output
 	size_t target_cell_count = target_index_count / 6;
 
-	if (target_cell_count == 0)
-		return 0;
-
 	meshopt_Allocator allocator;
 
 	Vector3* vertex_positions = allocator.allocate<Vector3>(vertex_count);
@@ -1431,18 +1428,25 @@ size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* ind
 	const int kInterpolationPasses = 5;
 
 	// invariant: # of triangles in min_grid <= target_count
-	int min_grid = 0;
+	int min_grid = int(1.f / (target_error < 1e-3f ? 1e-3f : target_error));
 	int max_grid = 1025;
 	size_t min_triangles = 0;
 	size_t max_triangles = index_count / 3;
 
+	// when we're error-limited, we compute the triangle count for the min. size; this accelerates convergence and provides the correct answer when we can't use a larger grid
+	if (min_grid > 1)
+	{
+		computeVertexIds(vertex_ids, vertex_positions, vertex_count, min_grid);
+		min_triangles = countTriangles(vertex_ids, indices, index_count);
+	}
+
 	// instead of starting in the middle, let's guess as to what the answer might be! triangle count usually grows as a square of grid size...
 	int next_grid_size = int(sqrtf(float(target_cell_count)) + 0.5f);
 
 	for (int pass = 0; pass < 10 + kInterpolationPasses; ++pass)
 	{
-		assert(min_triangles < target_index_count / 3);
-		assert(max_grid - min_grid > 1);
+		if (min_triangles >= target_index_count / 3 || max_grid - min_grid <= 1)
+			break;
 
 		// we clamp the prediction of the grid size to make sure that the search converges
 		int grid_size = next_grid_size;
@@ -1471,16 +1475,18 @@ size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* ind
 			max_triangles = triangles;
 		}
 
-		if (triangles == target_index_count / 3 || max_grid - min_grid <= 1)
-			break;
-
 		// we start by using interpolation search - it usually converges faster
 		// however, interpolation search has a worst case of O(N) so we switch to binary search after a few iterations which converges in O(logN)
 		next_grid_size = (pass < kInterpolationPasses) ? int(tip + 0.5f) : (min_grid + max_grid) / 2;
 	}
 
 	if (min_triangles == 0)
+	{
+		if (out_result_error)
+			*out_result_error = 1.f;
+
 		return 0;
+	}
 
 	// build vertex->cell association by mapping all vertices with the same quantized position to the same cell
 	size_t table_size = hashBuckets2(vertex_count);
@@ -1503,18 +1509,26 @@ size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* ind
 
 	fillCellRemap(cell_remap, cell_errors, cell_count, vertex_cells, cell_quadrics, vertex_positions, vertex_count);
 
+	// compute error
+	float result_error = 0.f;
+
+	for (size_t i = 0; i < cell_count; ++i)
+		result_error = result_error < cell_errors[i] ? cell_errors[i] : result_error;
+
 	// collapse triangles!
 	// note that we need to filter out triangles that we've already output because we very frequently generate redundant triangles between cells :(
 	size_t tritable_size = hashBuckets2(min_triangles);
 	unsigned int* tritable = allocator.allocate<unsigned int>(tritable_size);
 
 	size_t write = filterTriangles(destination, tritable, tritable_size, indices, index_count, vertex_cells, cell_remap);
-	assert(write <= target_index_count);
 
 #if TRACE
-	printf("result: %d cells, %d triangles (%d unfiltered)\n", int(cell_count), int(write / 3), int(min_triangles));
+	printf("result: %d cells, %d triangles (%d unfiltered), error %e\n", int(cell_count), int(write / 3), int(min_triangles), sqrtf(result_error));
 #endif
 
+	if (out_result_error)
+		*out_result_error = sqrtf(result_error);
+
 	return write;
 }