feat: add show mask chip for tools

web/src/lib/core/effects.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { vignette } from "./effects";
+import { vignette, vignetteMask } from "./effects";
 import { makeImage } from "./test-helpers";
 
 describe("vignette", () => {
@@ -17,3 +17,19 @@ describe("vignette", () => {
 		expect(centerR).toBeGreaterThan(150);
 	});
 });
+
+describe("vignetteMask", () => {
+	it("white at corners, black at center, opaque", () => {
+		const out = vignetteMask(7, 7, 80);
+		const center = out.data[(3 * 7 + 3) * 4];
+		const corner = out.data[0];
+		expect(corner).toBeGreaterThan(center);
+		expect(corner).toBeGreaterThan(100);
+		expect(out.data[3]).toBe(255);
+	});
+
+	it("zero strength -> all black", () => {
+		const out = vignetteMask(3, 3, 0);
+		expect(Math.max(...out.data.filter((_, i) => i % 4 !== 3))).toBe(0);
+	});
+});