1 files changed, 26 insertions, 0 deletions
diff --git a/apps/web/src/masks/param-update.ts b/apps/web/src/masks/param-update.ts
new file mode 100644
index 00000000..e5c7f5b7
--- /dev/null
+++ b/apps/web/src/masks/param-update.ts
@@ -0,0 +1,26 @@
+import { FEATHER_HANDLE_SCALE, MAX_FEATHER } from "@/masks/feather";
+
+export function computeFeatherUpdate({
+	startFeather,
+	deltaX,
+	deltaY,
+	directionX,
+	directionY,
+}: {
+	startFeather: number;
+	deltaX: number;
+	deltaY: number;
+	directionX: number;
+	directionY: number;
+}): { feather: number } {
+	const projection = deltaX * directionX + deltaY * directionY;
+	return {
+		feather: Math.max(
+			0,
+			Math.min(
+				MAX_FEATHER,
+				Math.round(startFeather + projection / FEATHER_HANDLE_SCALE),
+			),
+		),
+	};
+}