1 files changed, 64 insertions, 0 deletions
diff --git a/apps/web/src/lib/masks/utils.ts b/apps/web/src/lib/masks/utils.ts
new file mode 100644
index 00000000..a9110237
--- /dev/null
+++ b/apps/web/src/lib/masks/utils.ts
@@ -0,0 +1,64 @@
+const LINE_PARALLEL_EPSILON = 1e-10;
+
+export function lineEdgeIntersection({
+	lineX,
+	lineY,
+	normalX,
+	normalY,
+	x1,
+	y1,
+	x2,
+	y2,
+}: {
+	lineX: number;
+	lineY: number;
+	normalX: number;
+	normalY: number;
+	x1: number;
+	y1: number;
+	x2: number;
+	y2: number;
+}): { x: number; y: number } | null {
+	const distance1 = halfPlaneSign({
+		lineX,
+		lineY,
+		normalX,
+		normalY,
+		x: x1,
+		y: y1,
+	});
+	const distance2 = halfPlaneSign({
+		lineX,
+		lineY,
+		normalX,
+		normalY,
+		x: x2,
+		y: y2,
+	});
+	const denom = distance1 - distance2;
+	if (Math.abs(denom) < LINE_PARALLEL_EPSILON) return null;
+	const t = distance1 / denom;
+	if (t < 0 || t > 1) return null;
+	return {
+		x: x1 + (x2 - x1) * t,
+		y: y1 + (y2 - y1) * t,
+	};
+}
+
+export function halfPlaneSign({
+	lineX,
+	lineY,
+	normalX,
+	normalY,
+	x,
+	y,
+}: {
+	lineX: number;
+	lineY: number;
+	normalX: number;
+	normalY: number;
+	x: number;
+	y: number;
+}): number {
+	return (x - lineX) * normalX + (y - lineY) * normalY;
+}