fix matrixVecMul4 implementation

Author: wcandillon

package/src/renderer/__tests__/e2e/Matrix4.spec.tsx

@@ -10,6 +10,8 @@ import {
   rotateX,
   translate,
   toMatrix3,
+  Matrix4,
+  mapPoint3d,
 } from "../../../skia/types";
 
 const ckPerspective = (d: number) => [
@@ -225,4 +227,17 @@ describe("Matrix4", () => {
       0.1
     );
   });
+  it("should correctly transform a point with an identity matrix", () => {
+    const identityMatrix = Matrix4();
+    const point = [100, -100, 200] as const; // Define some test point
+    const result = mapPoint3d(identityMatrix, point);
+    expect(result).toEqual(point);
+  });
+  it("should correctly transform a point with a translation matrix", () => {
+    const translationMatrix = translate(100, 100, 100);
+    const point = [100, -100, 200] as const; // Define some test point
+    const expectedResult = [200, 0, 300] as const;
+    const result = mapPoint3d(translationMatrix, point);
+    expect(result).toEqual(expectedResult);
+  });
 });

package/src/skia/types/Matrix4.ts

@@ -150,14 +150,16 @@ const rotatedUnitSinCos = (
   ];
 };
 
-const matrixVecMul4 = (m: Matrix4, v: Vec4) => {
+/**
+ * @worklet
+ */
+export const matrixVecMul4 = (m: Matrix4, v: Vec4): Vec4 => {
   "worklet";
-  const [vx, vy, vz, vw] = v;
   return [
-    vx * m[0] + vy * m[4] + vz * m[8] + vw * m[12],
-    vx * m[1] + vy * m[5] + vz * m[9] + vw * m[13],
-    vx * m[2] + vy * m[6] + vz * m[10] + vw * m[14],
-    vx * m[3] + vy * m[7] + vz * m[11] + vw * m[15],
+    m[0] * v[0] + m[1] * v[1] + m[2] * v[2] + m[3] * v[3],
+    m[4] * v[0] + m[5] * v[1] + m[6] * v[2] + m[7] * v[3],
+    m[8] * v[0] + m[9] * v[1] + m[10] * v[2] + m[11] * v[3],
+    m[12] * v[0] + m[13] * v[1] + m[14] * v[2] + m[15] * v[3],
   ];
 };