Examples: Use Taubin smoothing to prevent volume shrinkage.

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

Author: mrdoob

examples/jsm/sculpt/SculptTools.js

@@ -970,17 +970,34 @@ function toolSmooth( mesh, iVerts, intensity ) {
 	const mAr = mesh.getMaterials();
 	const nbVerts = iVerts.length;
 	const smoothVerts = new Float32Array( getMemory( nbVerts * 4 * 3 ), 0, nbVerts * 3 );
+
+	// Taubin lambda-mu smoothing: two passes to prevent volume shrinkage
+	const lambda = 0.5;
+	const mu = - 0.53;
+
+	// Forward pass (shrink)
 	laplacianSmooth( mesh, iVerts, smoothVerts );
 	for ( let i = 0; i < nbVerts; ++ i ) {
 
 		const ind = iVerts[ i ] * 3;
-		const vx = vAr[ ind ], vy = vAr[ ind + 1 ], vz = vAr[ ind + 2 ];
 		const i3 = i * 3;
-		const mI = intensity * mAr[ ind + 2 ];
-		const intComp = 1.0 - mI;
-		vAr[ ind ] = vx * intComp + smoothVerts[ i3 ] * mI;
-		vAr[ ind + 1 ] = vy * intComp + smoothVerts[ i3 + 1 ] * mI;
-		vAr[ ind + 2 ] = vz * intComp + smoothVerts[ i3 + 2 ] * mI;
+		const mI = intensity * mAr[ ind + 2 ] * lambda;
+		vAr[ ind ] += ( smoothVerts[ i3 ] - vAr[ ind ] ) * mI;
+		vAr[ ind + 1 ] += ( smoothVerts[ i3 + 1 ] - vAr[ ind + 1 ] ) * mI;
+		vAr[ ind + 2 ] += ( smoothVerts[ i3 + 2 ] - vAr[ ind + 2 ] ) * mI;
+
+	}
+
+	// Backward pass (expand to restore volume)
+	laplacianSmooth( mesh, iVerts, smoothVerts );
+	for ( let i = 0; i < nbVerts; ++ i ) {
+
+		const ind = iVerts[ i ] * 3;
+		const i3 = i * 3;
+		const mI = intensity * mAr[ ind + 2 ] * mu;
+		vAr[ ind ] += ( smoothVerts[ i3 ] - vAr[ ind ] ) * mI;
+		vAr[ ind + 1 ] += ( smoothVerts[ i3 + 1 ] - vAr[ ind + 1 ] ) * mI;
+		vAr[ ind + 2 ] += ( smoothVerts[ i3 + 2 ] - vAr[ ind + 2 ] ) * mI;
 
 	}