imagefilltoborder()

(PHP 4, PHP 5, PHP 7)

区域填充到指定颜色的边界为止

说明

imagefilltoborder(resource $image,int $x,int $y,int $border,int $color): bool

imagefilltoborder()从$x，$y（图像左上角为 0, 0）点开始用$color颜色执行区域填充，直到碰到颜色为$border的边界为止。【注：边界内的所有颜色都会被填充。如果指定的边界色和该点颜色相同，则没有填充。如果图像中没有该边界色，则整幅图像都会被填充。】

Very useful to build a pseudo-sphere with a color gradient...
<?php
 $width = 300;
 $center = $width / 2;
 $colordivs = 255 / $center;
 $im = @imagecreate($width, $width);
 $back_color = imagecolorallocate($im, 20, 30, 40);
 imagefill($im, 0, 0, $back_color); 
 for ($i = 0; $i <= $center; $i++)
 {
   $diametre = $width - 2 * $i;
  $el_color = imagecolorallocate($im, $i * $colordivs, 0, 0);
  imagearc($im, $center, $center, $diametre, $diametre, 0, 360, $el_color);
  imagefilltoborder($im, $center, $center, $el_color, $el_color);
 }
 imagepng($im);
?>
Dark Skull Software
http://www.darkskull.net

In the example below, for those with newer GD versions, it makes more sense to replace:
imagearc($im, $center, $center, $diametre, $diametre, 0, 360, $el_color);
with:
imageellipse($im, $center, $center, $diametre, $diametre, $el_color);
This is obviously simpler.