https://github.com/arenanet/api-cdi/issues/65 http://gw2.chillerlan.net/guildemblems.php?guild_id=75FD83CF-0C45-4834-BC4C-097F93A487AF

guildemblems.php

<?php
/**
 *
 */

// some settings
$config['path_background'] = 'img/background/'; // trailing slash!
$config['path_foreground'] = 'img/foreground/';
$config['path_cache'] = 'img/cache/';
$config['path_cacert'] = 'cert/cacert.pem';
$config['image_error'] = 'img/404-quaggan.png'; // 256x256

/**
 * Matrix-multiply
 *
 * adapted from
 * @link http://sickel.net/blogg/?p=907
 *
 * @param $m1
 * @param $m2
 *
 * @return array|bool
 */
function matrix_multiply($m1, $m2){
	$r = count($m1);
	$c = count($m2[0]);
	$p = count($m2);
	if(count($m1[0]) !== $p){
		return false; //incompatible matrix
	}
	$m3 = [];
	for($i = 0; $i < $r; $i++){
		for($j = 0; $j < $c; $j++){
			$m3[$i][$j] = 0;
			for($k = 0; $k < $p; $k++){
				$m3[$i][$j] += $m1[$i][$k]*$m2[$k][$j];
			}
		}
	}
	return ($m3);
}

/**
 * Color Matrix calculation
 *
 * An approach to get the correct RGB values from the GW2 color API as Cliff Spradlin described on the GW2 API forums.
 * The described function was split up in 2 functions to improve performance within long run loops e.g. image processing
 * as suggested by Dr Ishmael.
 *
 * @link https://forum-en.guildwars2.com/forum/community/api/How-To-Colors-API/2148826 Cliff's second description
 * @link https://forum-en.guildwars2.com/forum/community/api/API-Suggestion-Guilds/2155578 Dr Ishmael's suggestion
 *
 * @see  apply_color_transform()
 *
 * @param array $hslbc the content of the arrays [cloth,leather,metal] which are returned by the API
 *
 * @return array matrix for calculation in apply_color_transform()
 */
function get_color_matrix($hslbc){
	$h = ($hslbc['hue']*pi())/180;
	$s = $hslbc['saturation'];
	$l = $hslbc['lightness'];
	$b = $hslbc['brightness']/128;
	$c = $hslbc['contrast'];

	// 4x4 identity matrix
	$matrix = [
		[1, 0, 0, 0],
		[0, 1, 0, 0],
		[0, 0, 1, 0],
		[0, 0, 0, 1]
	];

	if($b !== 0 || $c !== 1){
		// process brightness and contrast
		$t = 128*(2*$b+1-$c);
		$mult = [
			[$c, 0, 0, $t],
			[0, $c, 0, $t],
			[0, 0, $c, $t],
			[0, 0, 0, 1]
		];
		$matrix = matrix_multiply($mult, $matrix);
	}

	if($h !== 0 || $s !== 1 || $l !== 1){
		// transform to HSL
		$multRgbToHsl = [
			[0.707107, 0, -0.707107, 0],
			[-0.408248, 0.816497, -0.408248, 0],
			[0.577350, 0.577350, 0.577350, 0],
			[0, 0, 0, 1]
		];
		$matrix = matrix_multiply($multRgbToHsl, $matrix);

		// process adjustments
		$cosHue = cos($h);
		$sinHue = sin($h);
		$mult = [
			[$cosHue*$s, $sinHue*$s, 0, 0],
			[-$sinHue*$s, $cosHue*$s, 0, 0],
			[0, 0, $l, 0],
			[0, 0, 0, 1]
		];
		$matrix = matrix_multiply($mult, $matrix);

		// transform back to RGB
		$multHslToRgb = [
			[0.707107, -0.408248, 0.577350, 0],
			[0, 0.816497, 0.577350, 0],
			[-0.707107, -0.408248, 0.577350, 0],
			[0, 0, 0, 1]
		];
		$matrix = matrix_multiply($multHslToRgb, $matrix);
	}

	return $matrix;
}

/**
 * Apply color transform
 *
 * @param array $matrix the matrix returned by get_color_matrix()
 * @param array $base   the base color provided in the API response, or calculated for the emblem colors
 *
 * @return array calculated RGB values
 */
function apply_color_transform($matrix, $base){
	// apply the color transformation
	$bgrVector = [
		[$base[2]],
		[$base[1]],
		[$base[0]],
		[1]
	];
	$matrix = matrix_multiply($matrix, $bgrVector);

	// clamp the values
	$rgb = [
		floor(max(0, min(255, $matrix[2][0]))),
		floor(max(0, min(255, $matrix[1][0]))),
		floor(max(0, min(255, $matrix[0][0])))
	];

	return $rgb;
}

/**
 * Image hue calculation
 *
 * @author Moturdrn.2837
 * @link   https://gist.github.com/moturdrn/9d03a0cd4967828ac6cc
 *
 * @param resource $im  image
 * @param array    $col the [material] array from the color API response
 */
function imagehue($im, $col){
	$w = imagesx($im);
	$h = imagesy($im);
	$m = get_color_matrix($col);
	for($x = 0; $x < $w; $x++){
		for($y = 0; $y < $h; $y++){
			$ci = imagecolorsforindex($im, imagecolorat($im, $x, $y));
			if($ci['alpha'] < 127){
				$rgb = apply_color_transform($m, [$ci['red'], $ci['green'], $ci['blue']]);
				imagesetpixel($im, $x, $y, imagecolorallocatealpha($im, $rgb[0], $rgb[1], $rgb[2], $ci['alpha']));
			}
		}
	}
}

/**
 * Based on the script by Moturdrn.2837
 * https://gist.github.com/moturdrn/9d03a0cd4967828ac6cc
 *
 * @param resource $img
 * @param bool     $vertical
 *
 * @return resource
 */
function image_flip($img, $vertical = false){
	$w = imagesx($img);
	$h = imagesy($img);
	$dest = imagecreatetruecolor($w, $h);
	imagesavealpha($dest, true);
	imagefill($dest, 0, 0, imagecolorallocatealpha($dest, 0, 0, 0, 127));
	if($vertical){
		for($i = 0; $i < $h; $i++){
			imagecopy($dest, $img, 0, ($h-$i-1), 0, $i, $w, 1);
		}
	}
	else{
		for($i = 0; $i < $w; $i++){
			imagecopy($dest, $img, ($w-$i-1), 0, $i, 0, 1, $h);
		}
	}
	return $dest;
}

/**
 * An error image
 *
 * @param $size
 */
function image_error($size){
	global $config;
	header('Content-type: image/png');
	$img = imagecreatefrompng($config['image_error']);
	$thumb = imagecreatetruecolor($size, $size);
	imagecopyresampled($thumb, $img, 0, 0, 0, 0, $size, $size, 256, 256);
	imagepng($thumb);
	imagedestroy($thumb);
	exit();
}

/**
 * GW2 API request
 *
 * sends a request to the given API endpoint and fills $api_response on success
 *
 * @param string $endpoint
 * @param array  $params
 * @param string $apikey
 *
 * @return array|bool
 */
function api_request($endpoint, array $params = [], $apikey = ''){
	global $config;

	$url = 'https://api.guildwars2.com/'.$endpoint;
	$url .= count($params) > 0 ? '?'.http_build_query($params) : '';

	$options = [
		CURLOPT_URL            => $url,
#		CURLOPT_VERBOSE        => true,
#		CURLOPT_HEADER         => true,
		CURLOPT_SSL_VERIFYPEER => true,
		CURLOPT_SSL_VERIFYHOST => 2,
		CURLOPT_CAINFO         => dirname(__FILE__).'/'.$config['path_cacert'],
		CURLOPT_RETURNTRANSFER => true,
	];

	// since the format of an API key may change, we just check if it's present
	if(!empty($apikey)){
		$options += [
			CURLOPT_HTTPHEADER => [
				'Authorization: Bearer '.$apikey,
			]
		];
	}

	$ch = curl_init();
	curl_setopt_array($ch, $options);

	$data = curl_exec($ch);
	$info = curl_getinfo($ch);
	$errno = curl_errno($ch);
	$errstr = curl_error($ch);

	curl_close($ch);

	if(in_array($info['http_code'], [200, 206], true)){
		return json_decode($data, true);
	}
	else{
		return 'connection error: '.$errno.', '.$errstr."\n".print_r($info, true);
	}

}

/*********************
 * There be dragons. *
 *********************/

// get the size and clamp if needed
$size = isset($_GET['size']) && !empty($_GET['size']) ? max(40, min(256, intval($_GET['size']))) : 256;

// i cant't work without guild data...
if(!isset($_GET['guild_id']) || empty($_GET['guild_id'])){
	image_error($size);
}

// cache path/image name
$cachefile = $config['path_cache'].sha1($_GET['guild_id'].$size).'.png';

// first check if there is a cached image
#if(is_file($cachefile)){
#	header('Content-type: image/png');
#	readfile($cachefile);
#	exit;
#}

// get guild data. it's recommended to build a local guild database to increase performance
$guild_data = api_request('v1/guild_details.json', ['guild_id' => $_GET['guild_id']]);

if(!$guild_data || !is_array($guild_data) || in_array('error', $guild_data)){
	image_error($size);
}

// determine the filenames+path
$file_background = $config['path_background'].$guild_data['emblem']['background_id'].'.png';
$file_foreground1 = $config['path_foreground'].$guild_data['emblem']['foreground_id'].'a.png';
$file_foreground2 = $config['path_foreground'].$guild_data['emblem']['foreground_id'].'b.png';

if(!is_file($file_background) || !is_file($file_foreground1) || !is_file($file_foreground2)){
	image_error($size);
}

// it's highly recommended to pull the color data (~160kb API response)
// from a database or local .json since it's pretty static anyway.
$color_data = api_request('v2/colors', ['ids' => 'all']);
$color_data = array_combine(array_column($color_data, 'id'), $color_data);

// get the colors
$colors = [
	'background'  => $color_data[$guild_data['emblem']['background_color_id']]['cloth'],
	'foreground1' => $color_data[$guild_data['emblem']['foreground_primary_color_id']]['cloth'],
	'foreground2' => $color_data[$guild_data['emblem']['foreground_secondary_color_id']]['cloth'],
];

// fetch the images
$images = [
	'background'  => imagecreatefrompng($file_background),
	'foreground1' => imagecreatefrompng($file_foreground1),
	'foreground2' => imagecreatefrompng($file_foreground2),
];

// Apply transparency information for the background - PHP GD Base image issue
imagecolortransparent($images['background'], imagecolorallocate($images['background'], 255, 255, 255));
imagealphablending($images['background'], true);
imagesavealpha($images['background'], true);

// re-color images and apply filters like i've described over here:
// https://forum-en.guildwars2.com/forum/community/api/API-Suggestion-Guilds/2155863
// not yet perfect, but the results are ok..
foreach(['background', 'foreground1', 'foreground2'] as $layer){
	imagehue($images[$layer], $colors[$layer]);
	imagefilter($images[$layer], IMG_FILTER_CONTRAST, $colors[$layer]['contrast']);
	imagefilter($images[$layer], IMG_FILTER_COLORIZE, $colors[$layer]['rgb'][0], $colors[$layer]['rgb'][1], $colors[$layer]['rgb'][2]);
}

// Combine the primary and secondary emblem image
imagecopy($images['foreground1'], $images['foreground2'], 0, 0, 0, 0, 256, 256);

//apply flags
if(in_array('FlipBackgroundHorizontal', $guild_data['emblem']['flags'])){
	$images['background'] = image_flip($images['background']);
}
if(in_array('FlipBackgroundVertical', $guild_data['emblem']['flags'])){
	$images['background'] = image_flip($images['background'], true);
}
if(in_array('FlipForegroundHorizontal', $guild_data['emblem']['flags'])){
	$images['foreground1'] = image_flip($images['foreground1']);
}
if(in_array('FlipForegroundVertical', $guild_data['emblem']['flags'])){
	$images['foreground1'] = image_flip($images['foreground1'], true);
}

// Combine the emblem and background
imagecopy($images['background'], $images['foreground1'], 0, 0, 0, 0, 256, 256);

// resize and save to cache
if($size < 256){
	$thumb = imagecreate($size, $size);
	imagecopyresampled($thumb, $images['background'], 0, 0, 0, 0, $size, $size, 256, 256);
#	imageantialias($thumb, true);
	imagepng($thumb, $cachefile);
	imagedestroy($thumb);
}
else{
#	imageantialias($images['background'], true);
	imagepng($images['background'], $cachefile);
}

// output and clean up
header('Content-type: image/png');
readfile($cachefile);
imagedestroy($images['background']);
imagedestroy($images['foreground1']);
imagedestroy($images['foreground2']);