php--如何创建画布

<?php
/**
 * Created by PhpStorm.
 */

$my_image = Imagecreate(300,300);


$white = imagecolorallocate($my_image,255,255,255);  //第一个颜色作为背景色
$red = imagecolorallocate($my_image,255,0,0);
$blue = imagecolorallocate($my_image,0,0,255);
$black = imagecolorallocate($my_image,0,0,0);

imagerectangle($my_image,15,15,95,155,$red);
imagerectangle($my_image,95,155,175,295,$blue);
imagerectangle($my_image,175,15,255,155,$black);
header("Content-type:image/png");
imagepng($my_image);

imagedestroy($my_image);