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.png

变成正圆后：

变成正圆后.png

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

  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;
    }

参考