将bitmap裁剪为圆形

/**
 * 转换图片成圆形
 *
 * @param bitmap 传入Bitmap对象
 * @return
 */
public static 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, Bitmap.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，第一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(PorterDuff.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;
}