PHP GD从图片中切出三角形

Question

指南：使用PHP和GD库

我有普通图片（png | gif | jpeg）并且想要切出三角形。 为了方便我们假设我们想要剪切4个部分的图像，每个三角形从 中心开始。你说对了？

与GD画三角形是这样的：

<?php 
//create a white canvas 
$im = @imagecreate(500, 500) or die("Cannot Initialize new GD image stream"); 
imagecolorallocate($im, 255, 255, 255); 
//triangle 
$t1 = rand(0,400); 
$t2 = rand(0,400); 
$t3 = rand(10,100); 
$t4 = rand(10,100); 
$points = array(
$t1, $t2, 
($t1+$t3), $t2, 
$t1, ($t2+$t4) 
); 
$trcol = imagecolorallocate($im, rand(0,255), rand(0,255), rand(0,255)); 
imagefilledpolygon($im, $points, 3, $trcol); 
//make png and clean up 
header("Content-type: image/png"); 
imagepng($im); 
imagedestroy($im); 
?> 

现在我们其实想从一个已经存在的画面切换的三角形。 我只知道如何从现有的图片切出一个长方形这样：

<?php 
// Create image instances 
$src = imagecreatefromgif('php.gif'); 
$dest = imagecreatetruecolor(80, 40); 

// Copy 
imagecopy($dest, $src, 0, 0, 20, 13, 80, 40); 

// Output and free from memory 
header('Content-Type: image/gif'); 
imagegif($dest); 

imagedestroy($dest); 
imagedestroy($src); 
?> 

PHP GD imagecopy 布尔imagecopy的（资源$ dst_im和资源$ src_im分别，诠释$ dst_x，诠释$ dst_y，诠释$从src_x， int $ src_y，int $ src_w，int $ src_h）

那么我们如何将这两种方法结合起来做什么呢？

Answer 1

我确定x/y的计算可以用这个更加优化，但它适用于从给定图像生成顶部/右侧/底部/左侧三角形的png，并将它们输出为带有透明背景的png -

// Set which triangle to generate 
// top, right, bottom or left 

$triangle = 'top'; 

// Load source image 

$src  = imagecreatefromjpeg ('Desert.jpg'); 

// Get image width/height 

$srcWidth = imagesx ($src); 
$srcHeight = imagesy ($src); 

// Get centre position 

$centreX = floor ($srcWidth/2); 
$centreY = floor ($srcHeight/2); 

// Set new image size and start x/y 

switch ($triangle) 
{ 

    case 'top': 

     $destWidth = $srcWidth; 
     $destHeight = $centreY; 

     $destSX  = 0; 
     $destSY  = 0; 

     break; 

    case 'right': 

     $destWidth = $centreX; 
     $destHeight = $srcHeight; 

     $destSX  = $centreX; 
     $destSY  = 0; 

     break; 

    case 'bottom': 

     $destWidth = $srcWidth; 
     $destHeight = $centreY; 

     $destSX  = 0; 
     $destSY  = $centreY; 

     break; 

    case 'left': 

     $destWidth = $centreX; 
     $destHeight = $srcHeight; 

     $destSX  = 0; 
     $destSY  = 0; 

     break; 

} 

// Create the image 

$dest   = imagecreatetruecolor ($destWidth, $destHeight); 

// Copy from source 

imagecopy ($dest, $src, 0, 0, $destSX, $destSY, $destWidth, $destHeight); 

// OK... we now have the correctly sized rectangle copied over from the source image 
// Lets cut it down and turn it into the triangle we want by removing the other triangles 
// We remove the area by defining another colour as transparent and creating shapes with that colour 

$colRed   = imagecolorallocatealpha ($dest, 255, 0, 0, 0); 
imagecolortransparent ($dest, $colRed); 

switch ($triangle) 
{ 

    case 'top': 

     imagefilledpolygon ($dest, array ($centreX, $destHeight, 0, 0, 0, $destHeight), 3, $colRed); 
     imagefilledpolygon ($dest, array ($centreX, $destHeight, $destWidth, 0, $destWidth, $destHeight), 3, $colRed); 
     break; 

    case 'right': 

     imagefilledpolygon ($dest, array (0, $centreY, 0, 0, $destWidth, 0), 3, $colRed); 
     imagefilledpolygon ($dest, array (0, $centreY, 0, $destHeight, $destWidth, $destHeight), 3, $colRed); 
     break; 

    case 'bottom': 

     imagefilledpolygon ($dest, array ($centreX, 0, 0, 0, 0, $destHeight), 3, $colRed); 
     imagefilledpolygon ($dest, array ($centreX, 0, $destWidth, 0, $destWidth, $destHeight), 3, $colRed); 
     break; 

    case 'left': 

     imagefilledpolygon ($dest, array ($destWidth, $centreY, 0, 0, $destWidth, 0), 3, $colRed); 
     imagefilledpolygon ($dest, array ($destWidth, $centreY, 0, $destHeight, $destWidth, $destHeight), 3, $colRed); 
     break; 

} 

// Output new image 

header ('Content-Type: image/png'); 
imagepng ($dest); 

// Clean up 

imagedestroy ($src); 
imagedestroy ($dest);