PHP GD cut Triangle from Picture

Guidelines: Using PHP and GD library

I have ordinary pictures (png|gif|jpeg) and want to cut out triangles. To facilitate lets assume we want to cut images in 4 parts, each triangle starting from the center. You got it?

Painting triangles with GD goes like this:

<?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);
?>

now we Actually want to CUT a triangle from an already existing picture. I only know how to cut out a rectangle from an existing picture like this:

<?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($开发者_C百科dest);

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

PHP GD imagecopy bool imagecopy ( resource $dst_im , resource $src_im , int $dst_x , int $dst_y , int $src_x , int $src_y , int $src_w , int $src_h )

So how do we combine these two approaches to do what is intented?

I'm sure the x/y calculation could be more optimised with this, but it works for generating a png with top/right/bottom/left triangles from a given image, and outputting them as a png with transparent background -

// 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);