How to mask Bitmap with LinearGradient shader properly?

问题

I'm trying to mask Bitmap with gradient alpha at bottom. Gradient size are fixed and independed of Bitmap size. But it draws incorrect: bottom of gradient at top, than top. What's wrong?

There is sample code:

final int GRADIENT_HEIGHT = 32;

public Bitmap addGradient(Bitmap src) {
    int w = src.getWidth();
    int h = src.getHeight();
    Bitmap overlay = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(overlay);

    canvas.drawBitmap(src, 0, 0, null);

    Paint paint = new Paint();
    LinearGradient shader = new LinearGradient(0, 0, 0, GRADIENT_HEIGHT, 0xFFFFFFFF, 0x00FFFFFF, TileMode.REPEAT);
    paint.setShader(shader);
    paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
    canvas.drawRect(0, h - GRADIENT_HEIGHT, w, h, paint);

    return overlay;
}

Thanks!

回答1:

Change your LinearGradient to this:

    LinearGradient shader = new LinearGradient(0,  h - GRADIENT_HEIGHT, 0, h, 0xFFFFFFFF, 0x00FFFFFF, Shader.TileMode.CLAMP);

来源：https://stackoverflow.com/questions/23657811/how-to-mask-bitmap-with-lineargradient-shader-properly