PHP image generates rounded corners

        /**
	 * @param  string  $imgpath 源图片路径
	 * @param  integer $radius  圆角半径长度默认为15,处理成圆型
	 * @return [type]           [description]
	 */
	function radius_img($imgpath = './t.png', $radius = 15) {
		$ext     = pathinfo($imgpath);
		$src_img = null;
		switch ($ext['extension']) {
		case 'jpg':
			$src_img = imagecreatefromjpeg($imgpath);
			break;
		case 'png':
			$src_img = imagecreatefrompng($imgpath);
			break;
		}
		$wh = getimagesize($imgpath);
		$w  = $wh[0];
		$h  = $wh[1];
		// $radius = $radius == 0 ? (min($w, $h) / 2) : $radius;
		$img = imagecreatetruecolor($w, $h);
		//这一句一定要有
		imagesavealpha($img, true);
		//拾取一个完全透明的颜色,最后一个参数127为全透明
		$bg = imagecolorallocatealpha($img, 255, 255, 255, 127);
		imagefill($img, 0, 0, $bg);
		$r = $radius; //圆 角半径
		for ($x = 0; $x < $w; $x++) {
			for ($y = 0; $y < $h; $y++) {
				$rgbColor = imagecolorat($src_img, $x, $y);
				if (($x >= $radius && $x <= ($w - $radius)) || ($y >= $radius && $y <= ($h - $radius))) {
					//不在四角的范围内,直接画
					imagesetpixel($img, $x, $y, $rgbColor);
				} else {
					//在四角的范围内选择画
					//上左
					$y_x = $r; //圆心X坐标
					$y_y = $r; //圆心Y坐标
					if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
						imagesetpixel($img, $x, $y, $rgbColor);
					}
					//上右
					$y_x = $w - $r; //圆心X坐标
					$y_y = $r; //圆心Y坐标
					if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
						imagesetpixel($img, $x, $y, $rgbColor);
					}
					//下左
					$y_x = $r; //圆心X坐标
					$y_y = $h - $r; //圆心Y坐标
					if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
						imagesetpixel($img, $x, $y, $rgbColor);
					}
					//下右
					$y_x = $w - $r; //圆心X坐标
					$y_y = $h - $r; //圆心Y坐标
					if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
						imagesetpixel($img, $x, $y, $rgbColor);
					}
				}
			}
		}
		return $img;
	}