Android裁剪图片为圆形图片

/**
* 转换图片成圆形
*
* @param bitmap
* 传入Bitmap对象
* @return
*/
public Bitmap toRoundBitmap(Bitmap bitmap) {
int width = bitmap.getWidth();
int height = bitmap.getHeight();
float roundPx;
float left, top, right, bottom, dst_left, dst_top, dst_right, dst_bottom;
if (width <= height) {
roundPx = width / 2;
left = 0;
top = 0;
right = width;
bottom = width;
height = width;
dst_left = 0;
dst_top = 0;
dst_right = width;
dst_bottom = width;
} else {
roundPx = height / 2;
float clip = (width – height) / 2;
left = clip;
right = width – clip;
top = 0;
bottom = height;
width = height;
dst_left = 0;
dst_top = 0;
dst_right = height;
dst_bottom = height;
}

Bitmap output = Bitmap.createBitmap(width, height, Config.ARGB_8888);
Canvas canvas = new Canvas(output);

final int color = 0xff424242;
final Paint paint = new Paint();
final Rect src = new Rect((int) left, (int) top, (int) right, (int) bottom);
final Rect dst = new Rect((int) dst_left, (int) dst_top, (int) dst_right, (int) dst_bottom);
final RectF rectF = new RectF(dst);

paint.setAntiAlias(true);// 设置画笔无锯齿

canvas.drawARGB(0, 0, 0, 0); // 填充整个Canvas
paint.setColor(color);

// 以下有两种方法画圆,drawRounRect和drawCircle
// canvas.drawRoundRect(rectF, roundPx, roundPx, paint);// 画圆角矩形，*个参数为图形显示区域，第二个参数和第三个参数分别是水平圆角半径和垂直圆角半径。
canvas.drawCircle(roundPx, roundPx, roundPx, paint);

paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));// 设置两张图片相交时的模式,参考http://trylovecatch.iteye.com/blog/1189452
canvas.drawBitmap(bitmap, src, dst, paint); //以Mode.SRC_IN模式合并bitmap和已经draw了的Circle

return output;
}

参考流程图 &  原理图：