一般要做正圆形图片，只能是正方形的基础上才能实现，否则就变成椭圆了，下面说说如何使长方形的图片生成正圆形图片
废话不多说，没图没真相，先上图吧：
原图：
变成正圆后：
下面上代码：
public static Bitmap makeRoundCorner(Bitmap bitmap)
{
int width = bitmap.getWidth();
int height = bitmap.getHeight();
int left = 0, top = 0, right = width, bottom = height;
float roundPx = height/2;
if (width > height) {
left = (width - height)/2;
top = 0;
right = left + height;
bottom = height;
} else if (height > width) {
left = 0;
top = (height - width)/2;
right = width;
bottom = top + width;
roundPx = width/2;
}
ZLog.i(TAG, "ps:"+ left +", "+ top +", "+ right +", "+ bottom);
Bitmap output = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(output);
int color = 0xff424242;
Paint paint = new Paint();
Rect rect = new Rect(left, top, right, bottom);
RectF rectF = new RectF(rect);
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(bitmap, rect, rect, paint);
return output;
}
下面再解释下：
由于图片是长方形，所以图片的 宽、高 肯定会有一边要小于另一边，要生成正方形就已最小的一边为基准，再来裁切定位另一边的显示范围
至于圆角的半径则是正方形宽的一半，用过 CSS 的就知道，画圆很方便 border-radius设为 50% 就可以了，都是一个道理
android 的 UI 真是太繁琐了
矩形画个圆角的代码：
public static Bitmap makeRoundCorner(Bitmap bitmap, int px)
{
int width = bitmap.getWidth();
int height = bitmap.getHeight();
Bitmap output = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(output);
int color = 0xff424242;
Paint paint = new Paint();
Rect rect = new Rect(0, 0, width, height);
RectF rectF = new RectF(rect);
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawRoundRect(rectF, px, px, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(bitmap, rect, rect, paint);
return output;
}