mrdoob#27905 Add volume calculator for 3d mesh

src/objects/Mesh.js

@@ -49,6 +49,39 @@ class Mesh extends Object3D {
 
 	}
 
+	volume(precision) {
+		function calculateVolume({ geometry, precision }) {
+			let volume = 0;
+			const vertices = geometry.attributes.position.array;
+			let indexes = geometry.index ? geometry.index.array : null;
+			function triangularVolume(p1, p2, p3) {
+				const v321 = p3.x * p2.y * p1.z;
+				const v231 = p2.x * p3.y * p1.z;
+				const v312 = p3.x * p1.y * p2.z;
+				const v132 = p2.x * p1.y * p3.z;
+				const v213 = p1.x * p3.y * p2.z;
+				const v123 = p1.x * p2.y * p3.z;
+				return (1.0 / 6.0) * (-v321 + v231 + v312 - v132 - v213 + v123);
+			}
+			if (!indexes) {
+				indexes = Array.from({ length: vertices.length / 3 }, (_, i) => i);
+			}
+			for (let i = 0; i < indexes.length; i += 3) {
+				const a = new THREE.Vector3().fromArray(vertices, indexes[i] * 3);
+				const b = new THREE.Vector3().fromArray(vertices, indexes[i + 1] * 3);
+				const c = new THREE.Vector3().fromArray(vertices, indexes[i + 2] * 3);
+				volume += triangularVolume(a, b, c);
+			}
+			if (precision) {
+				return Math.abs(volume);
+			} else {
+				return Math.abs(volume / 1000);
+			}
+		}
+		const vol = calculateVolume({ geometry: this.geometry, precision: precision });
+		return vol;
+	}
+
 	copy( source, recursive ) {
 
 		super.copy( source, recursive );

test/unit/src/objects/Mesh.tests.js

@@ -91,6 +91,11 @@ export default QUnit.module( 'Objects', () => {
 
 		} );
 
+		QUnit.todo( 'volume', ( assert ) => {
+
+			assert.ok( false, 'everything\'s gonna be alright' );
+
+		} );
 		QUnit.todo( 'updateMorphTargets', ( assert ) => {
 
 			assert.ok( false, 'everything\'s gonna be alright' );