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qa-include/util/image.php

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+<?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 $imagefile
+ * @param int $size
+ * @return bool|float
+ */
+function qa_image_file_too_big($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 $imagedata
+ * @param int $width
+ * @param int $height
+ * @param int $maxwidth
+ * @param int $maxheight
+ * @return null|string
+ */
+function qa_image_constrain_data($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 $maxheight
+ * @return bool
+ */
+function qa_image_constrain(&$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 $image
+ * @param $width
+ * @param $height
+ */
+function qa_gd_image_resize(&$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
+ */
+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;
+}