image.php

<?php
/*
	Question2Answer by Gideon Greenspan and contributors
	http://www.question2answer.org/

	File: qa-include/util/image.php
	Description: Some useful image-related functions (using GD)


	This program is free software; you can redistribute it and/or
	modify it under the terms of the GNU General Public License
	as published by the Free Software Foundation; either version 2
	of the License, or (at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	More about this license: http://www.question2answer.org/license.php
*/

if (!defined('QA_VERSION')) { // don't allow this page to be requested directly from browser
	header('Location: ../../');
	exit;
}


/**
 * Return true if PHP has the GD extension installed and it appears to be usable
 */
function qa_has_gd_image()
{
	return extension_loaded('gd') && function_exists('imagecreatefromstring') && function_exists('imagejpeg');
}


/**
 * Check if the image in $imagefile will be too big for PHP/GD to process given memory usage and limits
 * Pass the width and height limit beyond which the image will require scaling in $size (if any)
 * Returns false if the image will fit fine, otherwise a safe estimate of the factor the image should be sized by
 * @param string $imagefile
 * @param int|null $size
 * @return bool|float
 */
function qa_image_file_too_big($imagefile, $size = null)
{
	if (function_exists('memory_get_usage')) {
		$gotbytes = trim(@ini_get('memory_limit'));

		$gotbytes = convert_to_bytes(substr($gotbytes, -1), $gotbytes);

		if ($gotbytes > 0) { // otherwise we clearly don't know our limit
			$gotbytes = ($gotbytes - memory_get_usage()) * 0.9; // safety margin of 10%

			$needbytes = filesize($imagefile); // memory to store file contents

			$imagesize = @getimagesize($imagefile);

			if (is_array($imagesize)) { // if image can't be parsed, don't worry about anything else
				$width = $imagesize[0];
				$height = $imagesize[1];
				$bits = isset($imagesize['bits']) ? $imagesize['bits'] : 8; // these elements can be missing (PHP bug) so assume this as default
				$channels = isset($imagesize['channels']) ? $imagesize['channels'] : 3; // for more info: http://gynvael.coldwind.pl/?id=223

				$needbytes += $width * $height * $bits * $channels / 8 * 2; // memory to load original image

				if (isset($size) && qa_image_constrain($width, $height, $size)) // memory for constrained image
					$needbytes += $width * $height * 3 * 2; // *2 here and above based on empirical tests
			}

			if ($needbytes > $gotbytes)
				return sqrt($gotbytes / ($needbytes * 1.5)); // additional 50% safety margin since JPEG quality may change
		}
	}

	return false;
}


/**
 * Given $imagedata containing JPEG/GIF/PNG data, constrain it proportionally to fit in $maxwidth x $maxheight.
 * Return the new image data (will always be a JPEG), and set the $width and $height variables.
 * If $maxheight is omitted or set to null, assume it to be the same as $maxwidth.
 * @param string $imagedata
 * @param int $width
 * @param int $height
 * @param int $maxwidth
 * @param int|null $maxheight
 * @return string|null
 */
function qa_image_constrain_data($imagedata, &$width, &$height, $maxwidth, $maxheight = null)
{
	$inimage = @imagecreatefromstring($imagedata);

	if (is_resource($inimage)) {
		$width = imagesx($inimage);
		$height = imagesy($inimage);

		// always call qa_gd_image_resize(), even if the size is the same, to take care of possible PNG transparency
		qa_image_constrain($width, $height, $maxwidth, $maxheight);
		qa_gd_image_resize($inimage, $width, $height);
	}

	if (is_resource($inimage)) {
		$imagedata = qa_gd_image_jpeg($inimage);
		imagedestroy($inimage);
		return $imagedata;
	}

	return null;
}


/**
 * Given and $width and $height, return true if those need to be contrained to fit in $maxwidth x $maxheight.
 * If so, also set $width and $height to the new proportionally constrained values.
 * If $maxheight is omitted or set to null, assume it to be the same as $maxwidth.
 * @param int $width
 * @param int $height
 * @param int $maxwidth
 * @param int|null $maxheight
 * @return bool
 */
function qa_image_constrain(&$width, &$height, $maxwidth, $maxheight = null)
{
	if (!isset($maxheight))
		$maxheight = $maxwidth;

	if ($width > $maxwidth || $height > $maxheight) {
		$multiplier = min($maxwidth / $width, $maxheight / $height);
		$width = floor($width * $multiplier);
		$height = floor($height * $multiplier);

		return true;
	}

	return false;
}


/**
 * Resize the GD $image to $width and $height, setting it to null if the resize failed
 * @param resource $image
 * @param int $width
 * @param int $height
 */
function qa_gd_image_resize(&$image, $width, $height)
{
	$oldimage = $image;
	$image = null;

	$newimage = imagecreatetruecolor($width, $height);
	$white = imagecolorallocate($newimage, 255, 255, 255); // fill with white first in case we have a transparent PNG
	imagefill($newimage, 0, 0, $white);

	if (is_resource($newimage)) {
		if (imagecopyresampled($newimage, $oldimage, 0, 0, 0, 0, $width, $height, imagesx($oldimage), imagesy($oldimage)))
			$image = $newimage;
		else
			imagedestroy($newimage);
	}

	imagedestroy($oldimage);
}


/**
 * Return the JPEG data for GD $image, also echoing it to browser if $output is true
 * @param resource $image
 * @param bool $output
 * @return string
 */
function qa_gd_image_jpeg($image, $output = false)
{
	ob_start();
	imagejpeg($image, null, 90);
	return $output ? ob_get_flush() : ob_get_clean();
}


/**
 * Return an array of strings listing the image formats that are supported
 * @return array
 */
function qa_gd_image_formats()
{
	$imagetypebits = imagetypes();

	$bitstrings = array(
		IMG_GIF => 'GIF',
		IMG_JPG => 'JPG',
		IMG_PNG => 'PNG',
	);

	foreach (array_keys($bitstrings) as $bit)
		if (!($imagetypebits & $bit))
			unset($bitstrings[$bit]);

	return $bitstrings;
}