先说下需求：前段时间神秘花园很火，于是乎客户想要制作神秘花园的网页游戏，涂色盘是圆形的，网页将涂色盘加载进当前的canvas中，当网友涂色完毕提交后，将canvas内容转化为图片数据传送至后台保存。这时接收到的数据包括整个canvas内容，整体是个矩形，除了网友涂色部分，还有整个背景、颜色盘、一些按钮之类的，这就需要把网友涂色的那个圆形部分裁剪下来。
我的思路分成两部分，首先裁剪成正方形，毕竟直接在矩形上面裁出一个圆相对来说麻烦一些。项目使用的thinkphp框架(v3.1)，裁正方形还是比较快捷的，直接调用自带的函数即可
import('ORG.Util.Image.ThinkImage');
$image = new ThinkImage(THINKIMAGE_GD, $file);
$image->crop(516,516,45,119)->save($file);//crop四个参数分别为长、宽、x偏移、y偏移
下一步就是要裁圆了，网上搜索了下居然没有搜索到多少有用的代码，感觉这个对大家都不是什么难处，看来自己这个半路出家的基础还是不太好呀。幸好在一个很老的帖子(08年的帖子)的回帖里面看到Sunyanzi@phpchina的一个思路，原帖地址传送门，代码如下：
<?php
//-----------------------------------------------------------
// * Sunyanzi @ phpchina
//-----------------------------------------------------------
class image_cutter {
private $original_image;
private $cutted_image;
private $diameter;
private $radius;
public function __construct( $image_path ) {
/* load the original image ... */
$image = imagecreatefromjpeg( $image_path );
/* get image size ... */
$x = imagesx( $image );
$y = imagesy( $image );
/* diameter of the circle is always the smaller side ... */
$this->diameter = $x > $y ? $y : $x;
/* radius is half a diameter ... am i must explain this ...? */
$this->radius = $this->diameter / 2;
/* save the original image ... */
$this->original_image = $image;
/* create new canvas to save our work ... */
$this->create_blank_image();
/* PAINTING TIME ... */
$this->read_the_original_image_and_write();
/* i'm positively bursting to see what we have done ... */
return;
}
private function __destruct() {
/* hey my dear brower ... it's not a html page comes ... */
header("Content-type: image/png");
/* show our work ... */
imagepng( $this->cutted_image );
/* we have to cleaned up the mass before left ... */
imagedestroy( $this->original_image );
imagedestroy( $this->cutted_image );
/* so ... how do you think about this ...? */
return;
}
private function create_blank_image() {
/* create a true color square whose side length equal to diameter of the circle ... */
$image = imagecreatetruecolor( $this->diameter,$this->diameter );
/* we also need a transparent background ... */
imagesavealpha($image, true);
/* create a transparent color ... */
$color = imagecolorallocatealpha($image, 0, 0, 0, 127);
/* ... then fill the image with it ... */
imagefill($image, 0, 0, $color);
/* nothing to do then ... just save the new image ... */
$this->cutted_image = $image;
/* go back and see what should we do next ..? */
return;
}
private function read_the_original_image_and_write() {
/* actually we need a smooth circle ... */
for ( $x = 0; $x <= $this->radius; $x += 0.01 ) {
/* standard form for the equation of a circle ... don't tell me you never knew that ... */
$y = sqrt( $this->diameter * $x - pow( $x , 2 ) ) + $this->radius;
/* i think i should call this successive scans ... */
for ( $i = $x; $i < $this->diameter - $x; $i++ ) {
/* half of the circle ... */
imagesetpixel (
$this->cutted_image , $i, $y,
imagecolorat( $this->original_image, $i, $y )
);
/* the other half of course ... */
imagesetpixel (
$this->cutted_image , $i, $this->diameter - $y,
imagecolorat( $this->original_image, $i, $this->diameter - $y )
);
}
}
/* avoid the white line when the diameter is an even number ... */
if ( ! is_float( $this->radius ) )
for ( $i = 0; $i < $this->diameter; $i++ )
imagesetpixel (
$this->cutted_image , $i, $this->radius - 1,
imagecolorat( $this->original_image, $i, $this->radius - 1 )
);
/* woo ... not as difficult as you think ... that's all ... */
return;
}
}
new image_cutter( HERE_COMES_THE_ORIGINAL_IMAGE_PATH );
?>
读了下代码，大概了解了下原理，以x轴为参考，0.01像素步长，通过圆的公式计算出对应y点的位置，然后将循环将X轴这条线上落在y点外（圆外）的点用透明色填充。实际放到项目中测试，发现个问题，由于项目中圆的半径比较大，516像素，按照0.01步长来计算，在x刚起步时，计算后的y值之间的间隔会大于1个像素，表现在页面上就是在圆的中间出现两条白线，将步长减少到0.004的时候白线消失，但是由于步长变小，整个循环数目变大，耗时严重，一次将近30秒的时间。
既然Sunyanzi提供了一个思路，那我就把它简化下，毕竟图片最小点是像素，那我就以1像素为步长，y轴也不计算了，直接也以1像素为步长，通过圆的方程式算出半径，比较半径的大小，大于我需要的圆的半径的点，把他用透明色填充掉就OK了。思路有了就开始动手。仅修改上面代码中裁圆的那个函数read_the_original_image_and_write()
private function read_the_original_image_and_write(){
for ( $x = 0; $x <= $this->radius; $x++ ) {
for ( $y = 0; $y <= $this->radius; $y++ ) {
if(sqrt( pow( $x- $this->radius , 2 ) + pow( $y- $this->radius , 2 ))<$this->radius){
imagesetpixel (
$this->cutted_image , $x, $y,
imagecolorat( $this->original_image, $x, $y )
);
imagesetpixel (
$this->cutted_image , $this->diameter - $x, $y,
imagecolorat( $this->original_image, $this->diameter - $x, $y )
);
imagesetpixel (
$this->cutted_image , $x, $this->diameter - $y,
imagecolorat( $this->original_image, $x, $this->diameter - $y )
);
imagesetpixel (
$this->cutted_image ,$this->diameter - $x, $this->diameter - $y,
imagecolorat( $this->original_image, $this->diameter - $x, $this->diameter - $y )
);
}
}
}
}
实际效果速度那是没说的，毕竟简化了，基本上秒出，效果相对之前的方法来说差了点，一周的锯齿感强了点，不过由于图片比较大，反倒不是很明显，有需要的话可以将步长调到0.5，效果会好一点，速度不是太影响，图片小的话可以放得更低一点。上面例子是直接输出图片，实际应用为保存成文件，这个就比较简单了，就不在这里贴代码了。
如何用PHP裁出一个圆
