void draw(SkCanvas* canvas) {

    SkPaint pRed;

    pRed.setColor(SK_ColorRED);

​

    SkPaint pSolidBlue;

    pSolidBlue.setColor(SK_ColorBLUE);

​

    SkPaint pThirtyBlue;

    pThirtyBlue.setColor(SK_ColorBLUE);

    pThirtyBlue.setAlphaf(0.3);

​

    SkPaint alpha;

    alpha.setAlphaf(0.3);

​

    // First row: Draw two opaque red rectangles into the 0th layer. Then draw two blue

    // rectangles overlapping the red, one is solid, the other is 30% transparent.

    canvas->drawRect(SkRect::MakeLTRB(10, 10, 60, 60), pRed);

    canvas->drawRect(SkRect::MakeLTRB(150, 10, 200, 60), pRed);

​

    canvas->drawRect(SkRect::MakeLTRB(30, 10, 80, 60), pSolidBlue);

    canvas->drawRect(SkRect::MakeLTRB(170, 10, 220, 60), pThirtyBlue);

​

    // Second row: Draw two opaque red rectangles into the 0th layer. Then save a new layer;

    // when the 1st layer gets merged onto the 0th layer (i.e. when restore() is called), it will

    // use the provided paint to do so. In this case, the paint is set to have 30% opacity, but

    // it could also have things set like blend modes or image filters.

    canvas->drawRect(SkRect::MakeLTRB(10, 70, 60, 120), pRed);

    canvas->drawRect(SkRect::MakeLTRB(150, 70, 200, 120), pRed);

​

    canvas->saveLayer(nullptr, &alpha);

​

    // In the 1st layer, draw the same blue overlapping rectangles as in the first row. Notice in

    // the final output, we have two different shades of purple. The layer's alpha made the

    // opaque blue rectangle transparent, and it made the transparent blue rectangle even more so

    canvas->drawRect(SkRect::MakeLTRB(30, 70, 80, 120), pSolidBlue);

    canvas->drawRect(SkRect::MakeLTRB(170, 70, 220, 120), pThirtyBlue);

​

    canvas->restore();

​

    // Third row: save the layer first, before drawing the two red rectangle, followed by the

    // overlapping blue rectangles. Notice that the blue overwrites the red in the same way as

    // the first row because the alpha of the layer is not applied until the layer is restored.

    canvas->saveLayer(nullptr, &alpha);

​

    canvas->drawRect(SkRect::MakeLTRB(10, 130, 60, 180), pRed);

    canvas->drawRect(SkRect::MakeLTRB(150, 130, 200, 180), pRed);

​

    canvas->drawRect(SkRect::MakeLTRB(30, 130, 80, 180), pSolidBlue);

    canvas->drawRect(SkRect::MakeLTRB(170, 130, 220, 180), pThirtyBlue);

​

    canvas->restore();

}