hand adjsutments

src/vr180player/xr/hand-aim.ts

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+export type VectorLike = {
+	x: number;
+	y: number;
+	z: number;
+};
+
+export type PalmAimInput = {
+	handedness?: string | null;
+	indexMetacarpal?: VectorLike | null;
+	middleMetacarpal?: VectorLike | null;
+	pinkyMetacarpal?: VectorLike | null;
+	ringMetacarpal?: VectorLike | null;
+	wrist?: VectorLike | null;
+};
+
+export type PalmAimRay = {
+	direction: VectorLike;
+	origin: VectorLike;
+};
+
+const MIN_AXIS_LENGTH_SQ = 0.000001;
+const PALM_SURFACE_OFFSET_METERS = 0.035;
+
+export function computePalmAimRay(input: PalmAimInput): PalmAimRay | null {
+	const { indexMetacarpal, pinkyMetacarpal, wrist } = input;
+	if (!indexMetacarpal || !pinkyMetacarpal || !wrist) {
+		return null;
+	}
+
+	const knuckleCenter = averageVectors([
+		indexMetacarpal,
+		input.middleMetacarpal,
+		input.ringMetacarpal,
+		pinkyMetacarpal
+	]);
+	if (!knuckleCenter) {
+		return null;
+	}
+
+	const fingerAxis = normalize(subtract(knuckleCenter, wrist));
+	const acrossPalmAxis = normalize(subtract(pinkyMetacarpal, indexMetacarpal));
+	if (!fingerAxis || !acrossPalmAxis) {
+		return null;
+	}
+
+	const direction = normalize(getPalmNormal(fingerAxis, acrossPalmAxis, input.handedness));
+	if (!direction) {
+		return null;
+	}
+
+	const palmCenter = lerp(wrist, knuckleCenter, 0.62);
+	const origin = add(palmCenter, scale(direction, PALM_SURFACE_OFFSET_METERS));
+	return { direction, origin };
+}
+
+function getPalmNormal(fingerAxis: VectorLike, acrossPalmAxis: VectorLike, handedness?: string | null): VectorLike {
+	if (handedness === 'left') {
+		return cross(acrossPalmAxis, fingerAxis);
+	}
+
+	return cross(fingerAxis, acrossPalmAxis);
+}
+
+function averageVectors(vectors: Array<VectorLike | null | undefined>): VectorLike | null {
+	const usableVectors = vectors.filter(Boolean) as VectorLike[];
+	if (usableVectors.length === 0) {
+		return null;
+	}
+
+	const total = usableVectors.reduce(
+		(sum, vector) => add(sum, vector),
+		{ x: 0, y: 0, z: 0 }
+	);
+	return scale(total, 1 / usableVectors.length);
+}
+
+function normalize(vector: VectorLike): VectorLike | null {
+	const lengthSq = vector.x * vector.x + vector.y * vector.y + vector.z * vector.z;
+	if (lengthSq < MIN_AXIS_LENGTH_SQ) {
+		return null;
+	}
+
+	const length = Math.sqrt(lengthSq);
+	return scale(vector, 1 / length);
+}
+
+function add(a: VectorLike, b: VectorLike): VectorLike {
+	return {
+		x: a.x + b.x,
+		y: a.y + b.y,
+		z: a.z + b.z
+	};
+}
+
+function subtract(a: VectorLike, b: VectorLike): VectorLike {
+	return {
+		x: a.x - b.x,
+		y: a.y - b.y,
+		z: a.z - b.z
+	};
+}
+
+function scale(vector: VectorLike, scalar: number): VectorLike {
+	return {
+		x: vector.x * scalar,
+		y: vector.y * scalar,
+		z: vector.z * scalar
+	};
+}
+
+function lerp(a: VectorLike, b: VectorLike, amount: number): VectorLike {
+	return {
+		x: a.x + (b.x - a.x) * amount,
+		y: a.y + (b.y - a.y) * amount,
+		z: a.z + (b.z - a.z) * amount
+	};
+}
+
+function cross(a: VectorLike, b: VectorLike): VectorLike {
+	return {
+		x: a.y * b.z - a.z * b.y,
+		y: a.z * b.x - a.x * b.z,
+		z: a.x * b.y - a.y * b.x
+	};
+}