Skia clip path test

void draw(SkCanvas* canvas) {
    const SkScalar scale = 256.0f;
    const SkScalar R = 0.45f * scale;
    const SkScalar TAU = 6.2831853f;
    SkPath path;
    path.moveTo(R, 0.0f);
    for (int i = 1; i < 7; ++i) {
        SkScalar theta = 3 * i * TAU / 7;
        path.lineTo(R * cos(theta), R * sin(theta));
    }
    path.close();
    SkPaint p;
    p.setAntiAlias(true);
    canvas->clear(SK_ColorWHITE);
    canvas->translate(0.5f * scale, 0.5f * scale);
    canvas->clipPath(path);
    canvas->clear(SK_ColorBLACK);
}