Examples: Use MWSELR vertex normals for sculpt shading.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mrdoob

examples/jsm/sculpt/SculptMesh.js

@@ -607,28 +607,63 @@ class SculptMesh {
 	_updateVerticesNormal( iVerts ) {
 
 		const nAr = this._normalsXYZ;
+		const vAr = this._verticesXYZ;
+		const fAr = this._facesABCD;
 		const faceNormals = this._faceNormals;
 		const ringFaces = this._vertRingFace;
 		const full = iVerts === undefined;
 		const nbVerts = full ? this._nbVertices : iVerts.length;
 
+		// MWSELR: weight = sin(angle) / (|e1| * |e2|)
+		// Since sin(angle) = |cross(e1,e2)| / (|e1|*|e2|),
+		// weight = |cross(e1,e2)| / (|e1|^2 * |e2|^2)
+
 		for ( let i = 0; i < nbVerts; ++ i ) {
 
 			const ind = full ? i : iVerts[ i ];
 			const vrf = ringFaces[ ind ];
+			const ind3 = ind * 3;
+			const vx = vAr[ ind3 ], vy = vAr[ ind3 + 1 ], vz = vAr[ ind3 + 2 ];
 			let nx = 0, ny = 0, nz = 0;
+
 			for ( let j = 0, l = vrf.length; j < l; ++ j ) {
 
-				const id = vrf[ j ] * 3;
-				nx += faceNormals[ id ];
-				ny += faceNormals[ id + 1 ];
-				nz += faceNormals[ id + 2 ];
+				const fId = vrf[ j ] * 4;
+				const iv1 = fAr[ fId ], iv2 = fAr[ fId + 1 ], iv3 = fAr[ fId + 2 ];
+
+				// Find the two other vertices of this face
+				let ov1, ov2;
+				if ( iv1 === ind ) { ov1 = iv2; ov2 = iv3; }
+				else if ( iv2 === ind ) { ov1 = iv3; ov2 = iv1; }
+				else { ov1 = iv1; ov2 = iv2; }
+
+				const o1 = ov1 * 3, o2 = ov2 * 3;
+				const e1x = vAr[ o1 ] - vx, e1y = vAr[ o1 + 1 ] - vy, e1z = vAr[ o1 + 2 ] - vz;
+				const e2x = vAr[ o2 ] - vx, e2y = vAr[ o2 + 1 ] - vy, e2z = vAr[ o2 + 2 ] - vz;
+
+				const len1sq = e1x * e1x + e1y * e1y + e1z * e1z;
+				const len2sq = e2x * e2x + e2y * e2y + e2z * e2z;
+				const denom = len1sq * len2sq;
+				if ( denom === 0 ) continue;
+
+				// cross(e1, e2) magnitude = sin(angle) * |e1| * |e2|
+				const cx = e1y * e2z - e1z * e2y;
+				const cy = e1z * e2x - e1x * e2z;
+				const cz = e1x * e2y - e1y * e2x;
+				const sinArea = Math.sqrt( cx * cx + cy * cy + cz * cz );
+
+				// weight = sinArea / (|e1|^2 * |e2|^2) = sin(angle) / (|e1| * |e2|)
+				const w = sinArea / denom;
+
+				const fnId = vrf[ j ] * 3;
+				nx += faceNormals[ fnId ] * w;
+				ny += faceNormals[ fnId + 1 ] * w;
+				nz += faceNormals[ fnId + 2 ] * w;
 
 			}
 
 			let len = Math.sqrt( nx * nx + ny * ny + nz * nz );
 			if ( len > 0 ) len = 1.0 / len;
-			const ind3 = ind * 3;
 			nAr[ ind3 ] = nx * len;
 			nAr[ ind3 + 1 ] = ny * len;
 			nAr[ ind3 + 2 ] = nz * len;