fix(🐛): scale SkMatrix uniformly when y is omitted

[dennytosp]

SkMatrix.scale() and postScale() declare y as optional:

scale: (x: number, y?: number) => SkMatrix;
postScale: (x: number, y?: number) => SkMatrix;

The two backends disagree on what omitting it means.

CanvasKit (JsiSkMatrix.ts) falls back to x — a uniform scale:

scale(x: number, y?: number) {
  this.preMultiply(this.CanvasKit.Matrix.scaled(x, y ?? x));
}

JSI (JsiSkMatrix.h) falls back to 1 — the y axis is left untouched:

void scale(double x, JsiOptional<double> y) {
  getObject()->preScale(x, y.has_value() ? *y : 1);
}

So matrix.scale(0.5) halves both axes on Web and only the x axis on iOS and Android.

Which one is right

The renderer's own test pins the uniform result:

// packages/skia/src/renderer/__tests__/Transform.spec.tsx
matrix.translate(origin.x, origin.y).scale(0.5).translate(-origin.x, -origin.y);
expect(matrix.get()).toStrictEqual([0.5, 0, 192, 0, 0.5, 192, 0, 0, 1]);
//                                            ^^^ scaleY is 0.5, not 1

That spec is not under e2e/, so it only ever runs against CanvasKit — which is why the native path was never covered. It also renders into snapshots/transform/scale-origin.png, the same baseline the transform={[{ scale: 0.5 }]} test uses, so the intent is unambiguous.

Fix

Default y to x in the JSI bindings. Not a recent regression — the 1 default predates the typed-bindings refactor in 6c95fc6.

Tests

packages/skia/src/skia/__tests__/Matrix.spec.ts covers scale, postScale, and the explicit two-argument form.

To be upfront: this spec exercises the CanvasKit backend, so it passes on main too — it pins the contract the JSI side now matches rather than reproducing the failure. I have no Skia build here to exercise JsiSkMatrix.h directly, so the C++ side rests on SkMatrix::preScale/postScale semantics and the expectation above. Worth a native run on your side before merging.

Full suite green: 749 passed, tsc --noEmit and eslint --max-warnings 0 clean, clang-format -n -Werror clean on the changed header.

[wcandillon]

@dennytosp Thank You for catching this. Can you update the test to use:

const result = await surface.eval((Skia) => {

See https://github.com/Shopify/react-native-skia/blob/main/packages/skia/CONTRIBUTING.md#writing-end-to-end-tests

that way it will run both against native and canvaskit. In its current form it only runs against canvaskit.

[dennytosp]

@wcandillon good catch, thank you — I had missed that the unit spec never touched the JSI side at all. It goes through surface.eval((Skia) => ...) now, in e2e/Matrix.spec.ts, so the native bindings are genuinely covered. Mind taking another pass?

[github-actions]

🎉 This PR is included in version 2.11.1 🎉

The release is available on:

• v2.11.1
• GitHub release

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