如何正确使用LinearGradient着色器屏蔽Bitmap？

Question

我正在尝试使用底部的渐变alpha屏蔽Bitmap。渐变大小是固定的，并且与位图大小无关。但它绘制不正确：顶部的渐变底部，而不是顶部。 怎么了？

有示例代码：

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;
}

谢谢！

Answer 1

将LinearGradient更改为：

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