A lightweight placeholder image generator that's pending a tidy up. Only requires a font in it's current directory. #php

placeholder.php

<?php
/*
 * Starbeamrainbowlabs' Placeholder Image Generation Service script
 *
 * Licensed under the Mozilla Public License 2.0
 * A copy of this license can be found here: https://www.mozilla.org/en-US/MPL/2.0/
 */

$exec_start = microtime(true);

if(isset($_GET["help"]))
{
	header("content-type: text/plain");
	exit("Starbeamrainbowlabs' Placeholder Service Help
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Welcome! You seem to have discovered my personal image placeholder service.
Please do not use this for production purposes - though you may use it
during development. Below is an explanation of the different GET paramters
and what they do.

Parameter   Default Value   Explanation
-------------------------------------------------------------------------------
width       640             The width of the image.
height      480             The height of the image.
angle       0               The angle of the text in degrees.
bg_colour   aaaaaa          The 6 digit hex code of the background colour
							without the preceding hash. Note that 3 digit hex
							codes will not work.
fg_colour   777777          The text colour in the same format as described
							above.
text        (undefined)     The text to use for the placeholder image. Omitting
							causes the image's dimensions to be used instead.
weight      normal          The font weight to use. Other supported values:
							bold.
quality     95              The quality to use when rendering the resulting
							jpeg.
hash		anything		Set to anything you like to cause the service to
							generate a different etag for caching. Also useful 
							for forcing the browser (or other application) to 
							download a separate placeholder image if you want
							multiple random ones.

Easter Eggs:
	fg_colour and bg_colour support special values of 'random' and 'inverse'.

Links:
	https://starbeamrainbowlabs.com/
	Email: feedback@starbeamrainbowlabs.com
	Twitter: @SBRLabs
	Reddit: /u/Starbeamrainbowlabs

If you want a copy of this script, just ask! I can be contacted through any of
the above (or in person if you know me IRL).

It's licensed under the Mozilla Public License 2.0 (MPL-2.0) - see that license here: https://www.mozilla.org/en-US/MPL/2.0/

--Starbeamrainbowlabs
");
}

// Settings
/// Admin Settings ///

// The maximum size allowed for the returned image
define("MAX_SIZE", 5000);

// Whether we should utilise etags to aid caching
define("ENABLE_CACHING", true);

// The length of time that caches should cache the placeholder for
define("CACHE_LENGTH", 60 * 60 * 24 * 7); // 7 days

// Whether to enable debug drawing for the text drawing angle.
define('DEBUG_ANGLE', false);


/// Settings from GET ///
$settings = new stdClass();
$settings->width = intval($_GET["width"] ?? 640);
$settings->height = intval($_GET["height"] ?? 480);
$settings->angle = intval($_GET["angle"] ?? 0);
$settings->bg_colour = trim($_GET["bg_colour"] ?? "aaaaaa");
$settings->fg_colour = trim($_GET["fg_colour"] ?? "777777");
$settings->text = $_GET["text"] ?? "text";
$settings->weight = trim($_GET["weight"] ?? "normal");
$settings->quality = intval($_GET["quality"] ?? 95);
$settings->hash = $_GET["hash"] ?? "";

/// Polyfills ///
// From https://github.com/ralouphie/getallheaders
// PHP-FPM doesn't have getallheaders() - but it looks likeit'll be fixed in 7.3.
if (!function_exists('getallheaders')) {
	/**
	 * Get all HTTP header key/values as an associative array for the current request.
	 *
	 * @return string[string] The HTTP header key/value pairs.
	 */
	function getallheaders()
	{
		$headers = [];
		$copy_server = [
			'CONTENT_TYPE'   => 'Content-Type',
			'CONTENT_LENGTH' => 'Content-Length',
			'CONTENT_MD5'	=> 'Content-Md5',
		];
		foreach ($_SERVER as $key => $value) {
			if (substr($key, 0, 5) === 'HTTP_') {
				$key = substr($key, 5);
				if (!isset($copy_server[$key]) || !isset($_SERVER[$key])) {
					$key = str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', $key))));
					$headers[$key] = $value;
				}
			} elseif (isset($copy_server[$key])) {
				$headers[$copy_server[$key]] = $value;
			}
		}
		if (!isset($headers['Authorization'])) {
			if (isset($_SERVER['REDIRECT_HTTP_AUTHORIZATION'])) {
				$headers['Authorization'] = $_SERVER['REDIRECT_HTTP_AUTHORIZATION'];
			} elseif (isset($_SERVER['PHP_AUTH_USER'])) {
				$basic_pass = isset($_SERVER['PHP_AUTH_PW']) ? $_SERVER['PHP_AUTH_PW'] : '';
				$headers['Authorization'] = 'Basic ' . base64_encode($_SERVER['PHP_AUTH_USER'] . ':' . $basic_pass);
			} elseif (isset($_SERVER['PHP_AUTH_DIGEST'])) {
				$headers['Authorization'] = $_SERVER['PHP_AUTH_DIGEST'];
			}
		}
		return $headers;
	}
}

/**
 * Draws a cross on the image.
 * @param	image	$image	The image to draw on.
 * @param	int		$x		The x co-ordinate
 * @param	int		$y		The y co-ordinate
 * @param	int		$size	The radius of the cross.
 * @param	colour	$colour	The colour to draw it in. Should be from imagecolorallocate().
 */
function imagecross(&$image, $x, $y, $size, $colour) {
	imageline($image, $x - $size, $y - $size, $x + $size, $y + $size, $colour);
	imageline($image, $x + $size, $y - $size, $x - $size, $y + $size, $colour);
}
/**
 * Put center-rotated ttf-text into image
 * Has the same signature as imagettftext().
 * @source	https://secure.php.net/manual/it/function.imagettftext.php#48938
 */
function imagettftext_center_rotate(&$im, $size, $angle, $x, $y, $color, $fontfile, $text, $debug = false)
{
	while($angle >= 360) $angle -= 360;
	while($angle < 0) $angle += 360;
	
	if($debug) {
		$debug_col_a = imagecolorallocate($im, 0, 255, 0);
		$debug_col_b = imagecolorallocate($im, 0, 0, 255);
		$debug_col_c = imagecolorallocate($im, 255, 0, 0);
		$debug_col_d = imagecolorallocate($im, 255, 255, 0);
		
		imagettftext($im, $size, $angle, $x, $y, $debug_col_b, $fontfile, $text);
		imagettftext($im, $size, 0, $x, $y, $debug_col_a, $fontfile, $text);
	}
	
	// retrieve boundingbox of the non rotated text
	$bbox = imagettfbbox($size, 0, $fontfile, $text);
	$orig_centre = [
		($bbox[0] + $bbox[2] + $bbox[4] + $bbox[6]) / 4,
		($bbox[1] + $bbox[3] + $bbox[5] + $bbox[7]) / 4
	];
	$text_width = $bbox[2] - $bbox[0];
	$text_height = $bbox[3] - $bbox[5];
	if($debug) header("x-text-rect: {$text_width} x {$text_height}");
	
	// Retrieve boundingbox of the rotated text
	$bbox = imagettfbbox($size, $angle, $fontfile, $text);
	$rot_centre = [
		($bbox[0] + $bbox[2] + $bbox[4] + $bbox[6]) / 4,
		($bbox[1] + $bbox[3] + $bbox[5] + $bbox[7]) / 4
	];
	
	// Calculate the x and y shifting needed
	$dx = $rot_centre[0] - $orig_centre[0];
	$dy = $rot_centre[1] - $orig_centre[1];
	
	// New pivot point
	$px = $x - ($dx + $text_width/2);
	// if($angle != 0) $px -= $text_width * 2 * $angle / 360;
	$py = $y - $dy + $text_height/2;
	
	header("x-centres: ($angle deg) ({$orig_centre[0]}, {$orig_centre[1]}), ({$rot_centre[0]}, {$rot_centre[1]}) -> ($px, $py)");

	// Output
	$result = imagettftext($im, $size, $angle, $px, $py, $color, $fontfile, $text);
	
	if($debug) {
		imagesetthickness($im, 8);
		imagecross($im, $px, $py, 1000, $debug_col_d);
		imagecross($im, $x, $y, 1000, $debug_col_c);
		imagecross($im, $orig_centre[0] + $x, $orig_centre[1] + $y, 1000, $debug_col_a);
		imagecross($im, $rot_centre[0] + $x, $rot_centre[1] + $y, 1000, $debug_col_b);
	}
	
	return $result;
}

/**
 * Extracts a colour from a hex code
 * @param	string	$string	The hex code to extract from.
 * @param	int		$index	The index from which to extract.
 * @return	int		The value of the channel at the specified index.
 */
function get_component($string, $index) {
	return hexdec(substr($string, $index * 2, 2));
}
/**
 * Returns a random hex colour.
 * @return	string	The randomly generated hex colour.
 */
function generate_random_colour() {
	$result = "";
	for($i = 0; $i < 6; $i++) // Hex colours are 6 digits long
		$result .= "0123456789abcdef"[random_int(0, 15)]; // Crypto random numbers are better
	return $result;
}
/**
 * Inverts the given hexadecimal colour.
 * @param	string	$hex	The hex colour to invert.
 * @return	string	The inverted hex colour.
 */
function invert_colour($hex) {
	return str_pad(dechex(255 - get_component($hex, 0)), 2, "0", STR_PAD_LEFT) . 
		str_pad(dechex(255 - get_component($hex, 1)), 2, "0", STR_PAD_LEFT) . 
		str_pad(dechex(255 - get_component($hex, 2)), 2, "0", STR_PAD_LEFT);
}


// Special colour handling

if($settings->bg_colour == "inverse" && $settings->fg_colour == "inverse")
	$settings->bg_colour = "random";

if($settings->bg_colour == "random")
	$settings->bg_colour = generate_random_colour();
if($settings->fg_colour == "random")
	$settings->fg_colour = generate_random_colour();

if($settings->bg_colour == "inverse")
	$settings->bg_colour = invert_colour($settings->fg_colour);
if($settings->fg_colour == "inverse")
	$settings->fg_colour = invert_colour($settings->bg_colour);

header("x-parsed-colours: '$settings->bg_colour' / '$settings->fg_colour'");

// Limit the maximum size of the returned image
if($settings->width < 0) $settings->width = 1;
if($settings->height < 0) $settings->height = 1;
if($settings->width > MAX_SIZE) $settings->width = MAX_SIZE;
if($settings->height > MAX_SIZE) $settings->height = MAX_SIZE;

// Set the font filename
$font_types = [ "normal", "bold" ];
$font_map = [ "Regular", "Bold" ];

if(!in_array($settings->weight, $font_types))
	$settings->weight = $font_types[0];

$settings->weight = str_replace($font_types, $font_map, strtolower($settings->weight));

$font_file = "./SourceSansPro-$settings->weight.ttf";


if(ENABLE_CACHING)
{
	// Get the request headers and work out if the requested placeholder is the
	// same as the one we are about to render
	$headers = getallheaders();
	$headers = array_change_key_case($headers, CASE_LOWER);
//	header("content-type: text/plain");
	$server_etag = sha1(json_encode($settings));
	if(isset($headers["if-none-match"]))
	{
		$headers["if-none-match"] = preg_replace("/[^0-9a-f]/i", "", $headers["if-none-match"]);
		if($headers["if-none-match"] == sha1(json_encode($settings)))
		{
			// The placeholder specified by the etag request is identical to the
			// one we were about to render
			http_response_code(304);
			header("x-generation-time: " . (microtime(true) - $exec_start) . "s");
			header("x-cache-status: if-none-match=foundmatched");
			exit();
		}
		header("x-cache-status: if-none-match=foundnotmatched");
	}
	else
	{
		header("x-cache-status: if-none-match=notfound");
	}
}

// Create the image
$image = imagecreatetruecolor($settings->width, $settings->height);

// Sort out the background colour
$bg_colour_parts = new stdClass();
$bg_colour_parts->r = get_component($settings->bg_colour, 0);
$bg_colour_parts->g = get_component($settings->bg_colour, 1);
$bg_colour_parts->b = get_component($settings->bg_colour, 2);
$bg_colour = imagecolorallocate($image, $bg_colour_parts->r, $bg_colour_parts->g, $bg_colour_parts->b);

imagefill($image, 0, 0, $bg_colour);

// Sort out the foreground colour
$fg_colour_parts = new stdClass();
$fg_colour_parts->r = get_component($settings->fg_colour, 0);
$fg_colour_parts->g = get_component($settings->fg_colour, 1);
$fg_colour_parts->b = get_component($settings->fg_colour, 2);
$fg_colour = imagecolorallocate($image, $fg_colour_parts->r, $fg_colour_parts->g, $fg_colour_parts->b);

// Determine the text we are going to draw
$text = $settings->text;
if(!isset($_GET["text"]))
	$text = "$settings->width x $settings->height";


// Calculate the size of the text
$text_bounding_percent = 0.9;
$text_size = 20;
$text_box = imagettfbbox($text_size, 0, $font_file, $text);
$text_width = $text_box[2] - $text_box[0];
$text_height = $text_box[0] - $text_box[6];

$target_width = $settings->width * $text_bounding_percent;
$target_height = $settings->height * $text_bounding_percent;

$text_scale = $target_width / $text_width;

//header("content-type: text/plain");

$text_size *= $text_scale;
$text_box = imagettfbbox($text_size, $settings->angle, $font_file, $text);
$text_width = $text_box[2] - $text_box[0];
$text_height = $text_box[0] - $text_box[6];

// Calculate the position of the text
$text_x = ($settings->width / 2) - ($text_width / 2);
$text_y = ($settings->height / 2) + ((($text_size / 96) * 72) / 2); // point -> pixel

imagettftext_center_rotate(
	$image,
	$text_size, $settings->angle,
	// $text_x, $text_y,
	$settings->width / 2, $settings->height / 2,
	$fg_colour, $font_file,
	$text,
	DEBUG_ANGLE
);

header("x-generation-time: " . (microtime(true) - $exec_start) . "s");
header("x-text-size: $text_size");
header("x-usage-help: Add 'help' GET param to request");

header("content-type: image/jpeg");
if(ENABLE_CACHING)
	header("etag: " . sha1(json_encode($settings)));
imagejpeg($image, null, $settings->quality);

?>