Android修改图片内容，使图片以渐变颜色展示

以下是在StackOverFlow上找到的答案，记录一下。

private Bitmap addGradient(Bitmap originalBitmap) {
    int width = originalBitmap.getWidth();
    int height = originalBitmap.getHeight();
    Bitmap updatedBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(updatedBitmap);
    canvas.drawBitmap(originalBitmap, 0, 0, null);

    Paint paint = new Paint();
    int[] colors = new int[4];
    switch (mColor) {
        case BLUE:
            colors[0] = 0xFF2E8CFF;
            colors[1] = 0xFF2E8CFF;
            colors[2] = 0xFF24DFED;
            colors[3] = 0xFF24DFED;
            break;
        case PURPLE:
            colors[0] = 0xFF8F4AD4;
            colors[1] = 0xFF8F4AD4;
            colors[2] = 0xFF5742CE;
            colors[3] = 0xFF5742CE;
            break;
        case LIGHT_GREEN:
            colors[0] = 0xFF2EE0FF;
            colors[1] = 0xFF2EE0FF;
            colors[2] = 0xFF24EDC4;
            colors[3] = 0xFF24EDC4;
            break;
    }
    float[] positions = new float[]{0.25f, 0.5f, 0.75f, 1};
    LinearGradient shader = new LinearGradient(0, 0, 0,
            height, colors, positions, Shader.TileMode.CLAMP);
    paint.setShader(shader);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawRect(0, 0, width, height, paint);
    return updatedBitmap;
}

效果图：