我在Android中有一个动态生成的位图,我希望从顶部边缘羽化,使边框区域在顶部完全透明,并逐渐变为完全不透明,略低于。
transparentPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
transparentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT));
Shader shader = new LinearGradient(0, 0, 0, 20,
Color.TRANSPARENT, Color.TRANSPARENT, Shader.TileMode.CLAMP);
transparentPaint.setShader(shader);
// the bitmap is dynamically generated beforehand
Canvas c = new Canvas(bitmap);
c.drawRect(0, 0, bitmapWidth, 20, transparentPaint);
你将如何实现这样的目标:
[在这种情况下只是最顶端]
答案 0 :(得分:7)
看一下这个例子:Make certain area of bitmap transparent on touch
以下是使用渐变绘画的方法:
Paint framePaint = new Paint();
for(int i = 1; i < 5; i++){
setFramePaint(framePaint, i, imageW, imageH);
myCanvas.drawPaint(framePaint);
}
...
private void setFramePaint(Paint p, int side, float iw, float ih){
// paint, side of rect, image width, image height
p.setShader(null);
p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
float borderSize = 0.1f; //relative size of border
//use the smaller image size to calculate the actual border size
float bSize = (iw > ih)? ih * borderSize: ih * borderSize;
float g1x = 0;
float g1y = 0;
float g2x = 0;
float g2y = 0;
int c1 = 0, c2 = 0;
if (side == 1){
//left
g1x = 0;
g1y = ih/2;
g2x = bSize;
g2y = ih/2;
c1 = Color.TRANSPARENT;
c2 = Color.BLACK;
}else if(side == 2){
//top
g1x = iw/2;
g1y = 0;
g2x = iw/2;
g2y = bSize;
c1 = Color.TRANSPARENT;
c2 = Color.BLACK;
}else if(side == 3){
//right
g1x = iw;
g1y = ih/2;
g2x = iw - bSize;
g2y = ih/2;
c1 = Color.TRANSPARENT;
c2 = Color.BLACK;
}else if(side == 4){
//bottom
g1x = iw/2;
g1y = ih;
g2x = iw/2;
g2y = ih - bSize;
c1 = Color.TRANSPARENT;
c2 = Color.BLACK;
}
p.setShader(new LinearGradient(g1x, g1y, g2x, g2y, c1, c2, Shader.TileMode.CLAMP));
}
答案 1 :(得分:1)
如果您可以接受白色边缘而不是透明,请尝试屏幕模式。在PorterDuff.Mode.SCREEN模式下,白色像素保持白色,黑色像素变为不可见。创建一个叠加位图,其边缘为白色,中间为黑色并与图像混合。这将创建一个位图,白色边缘渐渐淡入中间的照片。
答案 2 :(得分:-1)
Romain Guy使用了与你想要达到的效果非常相似的褪色,除了this effect之外,他还添加了圆角