feat(soba): add scale factor calculation for pivot controls

Author: nartc

libs/soba/misc/src/lib/scale-factor.ts

@@ -0,0 +1,33 @@
+import { NgtSize } from 'angular-three';
+import { Camera, Vector3 } from 'three';
+
+const tV0 = new Vector3();
+const tV1 = new Vector3();
+const tV2 = new Vector3();
+
+function getPoint2(point3: Vector3, camera: Camera, size: NgtSize) {
+	const widthHalf = size.width / 2;
+	const heightHalf = size.height / 2;
+	camera.updateMatrixWorld(false);
+	const vector = point3.project(camera);
+	vector.x = vector.x * widthHalf + widthHalf;
+	vector.y = -(vector.y * heightHalf) + heightHalf;
+	return vector;
+}
+
+function getPoint3(point2: Vector3, camera: Camera, size: NgtSize, zValue: number = 1) {
+	const vector = tV0.set((point2.x / size.width) * 2 - 1, -(point2.y / size.height) * 2 + 1, zValue);
+	vector.unproject(camera);
+	return vector;
+}
+
+export function calculateScaleFactor(point3: Vector3, radiusPx: number, camera: Camera, size: NgtSize) {
+	const point2 = getPoint2(tV2.copy(point3), camera, size);
+	let scale = 0;
+	for (let i = 0; i < 2; ++i) {
+		const point2off = tV1.copy(point2).setComponent(i, point2.getComponent(i) + radiusPx);
+		const point3off = getPoint3(point2off, camera, size, point2off.z);
+		scale = Math.max(scale, point3.distanceTo(point3off));
+	}
+	return scale;
+}