Android开发实现图片渐变融入背景效果

效果图：

15689482562051.png

主要通过修改图片的alpha通道值实现，离图片中心点越近alpha值越大，最大255，距离中心点越远alpha值越小最小0

 public Bitmap changeAlpha(Bitmap bitmap){
        int w = bitmap.getWidth();
        int h = bitmap .getHeight();
        Bitmap result = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_4444);

        int ratio = w >  h ?  h * 32768 / w : w * 32768 /  h;
        int r,g,b,a,color;

        int[] oldPx = new int[w * h];
        int[] newPx = new int[w * h];

        float Size =0.5f;
        int cx = w >> 1;
        int cy = h >> 1;
        int max = cx * cx + cy * cy;
        int min = (int)(max * (2 - Size));
        int diff = max - min;
        bitmap.getPixels(oldPx, 0, w, 0, 0, w, h);
        for (int x = 0; x < w; x++) {
            for (int y = 0; y < h; y++) {

                color = oldPx[x * h + y];
                r = Color.red(color);
                g = Color.green(color);
                b = Color.blue(color);
                a = Color.alpha(color);

                int dx = cx - x;
                int dy = cy - y;
                if (w > h){
                    dx = (dx * ratio) >> 15;
                }
                else{
                    dy = (dy * ratio) >> 15;
                }

                int distSq = dx * dx + dy * dy;
                float v =  ((float)distSq / diff) * 255;
                a = (int)(a+(v));
                a = (a > 255 ? 255 : (a < 0 ? 0 : a));
                newPx[x * h + y] = Color.argb(a,r, g, b);
            }
        }
        result.setPixels(newPx, 0, w, 0, 0, w, h);
        return result;
    }