godot/thirdparty/meshoptimizer/patches/attribute-aware-simplify-distance-only-metric.patch

diff --git a/thirdparty/meshoptimizer/simplifier.cpp b/thirdparty/meshoptimizer/simplifier.cpp
index d8d4a67391..3847afc736 100644
--- a/thirdparty/meshoptimizer/simplifier.cpp
+++ b/thirdparty/meshoptimizer/simplifier.cpp
@@ -20,7 +20,7 @@
 #define TRACESTATS(i) (void)0
 #endif
 
-#define ATTRIBUTES 8
+#define ATTRIBUTES 3
 
 // This work is based on:
 // Michael Garland and Paul S. Heckbert. Surface simplification using quadric error metrics. 1997
@@ -458,6 +458,7 @@ struct Collapse
 		float error;
 		unsigned int errorui;
 	};
+	float distance_error;
 };
 
 static float normalize(Vector3& v)
@@ -538,6 +539,34 @@ static float quadricError(const Quadric& Q, const Vector3& v)
 	return fabsf(r) * s;
 }
 
+static float quadricErrorNoAttributes(const Quadric& Q, const Vector3& v)
+{
+	float rx = Q.b0;
+	float ry = Q.b1;
+	float rz = Q.b2;
+
+	rx += Q.a10 * v.y;
+	ry += Q.a21 * v.z;
+	rz += Q.a20 * v.x;
+
+	rx *= 2;
+	ry *= 2;
+	rz *= 2;
+
+	rx += Q.a00 * v.x;
+	ry += Q.a11 * v.y;
+	rz += Q.a22 * v.z;
+
+	float r = Q.c;
+	r += rx * v.x;
+	r += ry * v.y;
+	r += rz * v.z;
+
+	float s = Q.w == 0.f ? 0.f : 1.f / Q.w;
+
+	return fabsf(r) * s;
+}
+
 static void quadricFromPlane(Quadric& Q, float a, float b, float c, float d, float w)
 {
 	float aw = a * w;
@@ -693,7 +722,7 @@ static void quadricUpdateAttributes(Quadric& Q, const Vector3& p0, const Vector3
 }
 #endif
 
-static void fillFaceQuadrics(Quadric* vertex_quadrics, const unsigned int* indices, size_t index_count, const Vector3* vertex_positions, const unsigned int* remap)
+static void fillFaceQuadrics(Quadric* vertex_quadrics, Quadric* vertex_no_attrib_quadrics, const unsigned int* indices, size_t index_count, const Vector3* vertex_positions, const unsigned int* remap)
 {
 	for (size_t i = 0; i < index_count; i += 3)
 	{
@@ -703,6 +732,9 @@ static void fillFaceQuadrics(Quadric* vertex_quadrics, const unsigned int* indic
 
 		Quadric Q;
 		quadricFromTriangle(Q, vertex_positions[i0], vertex_positions[i1], vertex_positions[i2], 1.f);
+		quadricAdd(vertex_no_attrib_quadrics[remap[i0]], Q);
+		quadricAdd(vertex_no_attrib_quadrics[remap[i1]], Q);
+		quadricAdd(vertex_no_attrib_quadrics[remap[i2]], Q);
 
 #if ATTRIBUTES
 		quadricUpdateAttributes(Q, vertex_positions[i0], vertex_positions[i1], vertex_positions[i2], Q.w);
@@ -713,7 +745,7 @@ static void fillFaceQuadrics(Quadric* vertex_quadrics, const unsigned int* indic
 	}
 }
 
-static void fillEdgeQuadrics(Quadric* vertex_quadrics, const unsigned int* indices, size_t index_count, const Vector3* vertex_positions, const unsigned int* remap, const unsigned char* vertex_kind, const unsigned int* loop, const unsigned int* loopback)
+static void fillEdgeQuadrics(Quadric* vertex_quadrics, Quadric* vertex_no_attrib_quadrics, const unsigned int* indices, size_t index_count, const Vector3* vertex_positions, const unsigned int* remap, const unsigned char* vertex_kind, const unsigned int* loop, const unsigned int* loopback)
 {
 	for (size_t i = 0; i < index_count; i += 3)
 	{
@@ -757,6 +789,9 @@ static void fillEdgeQuadrics(Quadric* vertex_quadrics, const unsigned int* indic
 
 			quadricAdd(vertex_quadrics[remap[i0]], Q);
 			quadricAdd(vertex_quadrics[remap[i1]], Q);
+
+			quadricAdd(vertex_no_attrib_quadrics[remap[i0]], Q);
+			quadricAdd(vertex_no_attrib_quadrics[remap[i1]], Q);
 		}
 	}
 }
@@ -861,7 +896,7 @@ static size_t pickEdgeCollapses(Collapse* collapses, const unsigned int* indices
 	return collapse_count;
 }
 
-static void rankEdgeCollapses(Collapse* collapses, size_t collapse_count, const Vector3* vertex_positions, const Quadric* vertex_quadrics, const unsigned int* remap)
+static void rankEdgeCollapses(Collapse* collapses, size_t collapse_count, const Vector3* vertex_positions, const Quadric* vertex_quadrics, const Quadric* vertex_no_attrib_quadrics, const unsigned int* remap)
 {
 	for (size_t i = 0; i < collapse_count; ++i)
 	{
@@ -881,10 +916,14 @@ static void rankEdgeCollapses(Collapse* collapses, size_t collapse_count, const
 		float ei = quadricError(qi, vertex_positions[i1]);
 		float ej = quadricError(qj, vertex_positions[j1]);
 
+		const Quadric& naqi = vertex_no_attrib_quadrics[remap[i0]];
+		const Quadric& naqj = vertex_no_attrib_quadrics[remap[j0]];
+
 		// pick edge direction with minimal error
 		c.v0 = ei <= ej ? i0 : j0;
 		c.v1 = ei <= ej ? i1 : j1;
 		c.error = ei <= ej ? ei : ej;
+		c.distance_error = ei <= ej ? quadricErrorNoAttributes(naqi, vertex_positions[i1]) :  quadricErrorNoAttributes(naqj, vertex_positions[j1]);
 	}
 }
 
@@ -981,7 +1020,7 @@ static void sortEdgeCollapses(unsigned int* sort_order, const Collapse* collapse
 	}
 }
 
-static size_t performEdgeCollapses(unsigned int* collapse_remap, unsigned char* collapse_locked, Quadric* vertex_quadrics, const Collapse* collapses, size_t collapse_count, const unsigned int* collapse_order, const unsigned int* remap, const unsigned int* wedge, const unsigned char* vertex_kind, const Vector3* vertex_positions, const EdgeAdjacency& adjacency, size_t triangle_collapse_goal, float error_limit, float& result_error)
+static size_t performEdgeCollapses(unsigned int* collapse_remap, unsigned char* collapse_locked, Quadric* vertex_quadrics, Quadric* vertex_no_attrib_quadrics, const Collapse* collapses, size_t collapse_count, const unsigned int* collapse_order, const unsigned int* remap, const unsigned int* wedge, const unsigned char* vertex_kind, const Vector3* vertex_positions, const EdgeAdjacency& adjacency, size_t triangle_collapse_goal, float error_limit, float& result_error)
 {
 	size_t edge_collapses = 0;
 	size_t triangle_collapses = 0;
@@ -1043,6 +1082,7 @@ static size_t performEdgeCollapses(unsigned int* collapse_remap, unsigned char*
 		assert(collapse_remap[r1] == r1);
 
 		quadricAdd(vertex_quadrics[r1], vertex_quadrics[r0]);
+		quadricAdd(vertex_no_attrib_quadrics[r1], vertex_no_attrib_quadrics[r0]);
 
 		if (vertex_kind[i0] == Kind_Complex)
 		{
@@ -1080,7 +1120,7 @@ static size_t performEdgeCollapses(unsigned int* collapse_remap, unsigned char*
 		triangle_collapses += (vertex_kind[i0] == Kind_Border) ? 1 : 2;
 		edge_collapses++;
 
-		result_error = result_error < c.error ? c.error : result_error;
+		result_error = result_error < c.distance_error ? c.distance_error : result_error;
 	}
 
 #if TRACE
@@ -1469,9 +1509,11 @@ size_t meshopt_simplifyWithAttributes(unsigned int* destination, const unsigned
 
 	Quadric* vertex_quadrics = allocator.allocate<Quadric>(vertex_count);
 	memset(vertex_quadrics, 0, vertex_count * sizeof(Quadric));
+	Quadric* vertex_no_attrib_quadrics = allocator.allocate<Quadric>(vertex_count);
+	memset(vertex_no_attrib_quadrics, 0, vertex_count * sizeof(Quadric));
 
-	fillFaceQuadrics(vertex_quadrics, indices, index_count, vertex_positions, remap);
-	fillEdgeQuadrics(vertex_quadrics, indices, index_count, vertex_positions, remap, vertex_kind, loop, loopback);
+	fillFaceQuadrics(vertex_quadrics, vertex_no_attrib_quadrics, indices, index_count, vertex_positions, remap);
+	fillEdgeQuadrics(vertex_quadrics, vertex_no_attrib_quadrics, indices, index_count, vertex_positions, remap, vertex_kind, loop, loopback);
 
 	if (result != indices)
 		memcpy(result, indices, index_count * sizeof(unsigned int));
@@ -1502,7 +1544,7 @@ size_t meshopt_simplifyWithAttributes(unsigned int* destination, const unsigned
 		if (edge_collapse_count == 0)
 			break;
 
-		rankEdgeCollapses(edge_collapses, edge_collapse_count, vertex_positions, vertex_quadrics, remap);
+		rankEdgeCollapses(edge_collapses, edge_collapse_count, vertex_positions, vertex_quadrics, vertex_no_attrib_quadrics, remap);
 
 #if TRACE > 1
 		dumpEdgeCollapses(edge_collapses, edge_collapse_count, vertex_kind);
@@ -1521,7 +1563,7 @@ size_t meshopt_simplifyWithAttributes(unsigned int* destination, const unsigned
 		printf("pass %d: ", int(pass_count++));
 #endif
 
-		size_t collapses = performEdgeCollapses(collapse_remap, collapse_locked, vertex_quadrics, edge_collapses, edge_collapse_count, collapse_order, remap, wedge, vertex_kind, vertex_positions, adjacency, triangle_collapse_goal, error_limit, result_error);
+		size_t collapses = performEdgeCollapses(collapse_remap, collapse_locked, vertex_quadrics, vertex_no_attrib_quadrics, edge_collapses, edge_collapse_count, collapse_order, remap, wedge, vertex_kind, vertex_positions, adjacency, triangle_collapse_goal, error_limit, result_error);
 
 		// no edges can be collapsed any more due to hitting the error limit or triangle collapse limit
 		if (collapses == 0)