WordPress/wp-includes/media.php

<?php
/**
 * WordPress API for media display.
 *
 * @package WordPress
 */

/**
 * Scale down the default size of an image.
 *
 * This is so that the image is a better fit for the editor and theme.
 *
 * The $size parameter accepts either an array or a string. The supported string
 * values are 'thumb' or 'thumbnail' for the given thumbnail size or defaults at
 * 128 width and 96 height in pixels. Also supported for the string value is
 * 'medium' and 'full'. The 'full' isn't actually supported, but any value other
 * than the supported will result in the content_width size or 500 if that is
 * not set.
 *
 * Finally, there is a filter named, 'editor_max_image_size' that will be called
 * on the calculated array for width and height, respectively. The second
 * parameter will be the value that was in the $size parameter. The returned
 * type for the hook is an array with the width as the first element and the
 * height as the second element.
 *
 * @since 2.5.0
 * @uses wp_constrain_dimensions() This function passes the widths and the heights.
 *
 * @param int $width Width of the image
 * @param int $height Height of the image
 * @param string|array $size Size of what the result image should be.
 * @return array Width and height of what the result image should resize to.
 */
function image_constrain_size_for_editor($width, $height, $size = 'medium') {
	global $content_width;

	if ( is_array($size) ) {
		$max_width = $size[0];
		$max_height = $size[1];
	}
	elseif ( $size == 'thumb' || $size == 'thumbnail' ) {
		$max_width = intval(get_option('thumbnail_size_w'));
		$max_height = intval(get_option('thumbnail_size_h'));
		// last chance thumbnail size defaults
		if ( !$max_width && !$max_height ) {
			$max_width = 128;
			$max_height = 96;
		}
	}
	elseif ( $size == 'medium' ) {
		$max_width = intval(get_option('medium_size_w'));
		$max_height = intval(get_option('medium_size_h'));
		// if no width is set, default to the theme content width if available
	}
	elseif ( $size == 'large' ) {
		// we're inserting a large size image into the editor.  if it's a really
		// big image we'll scale it down to fit reasonably within the editor
		// itself, and within the theme's content width if it's known.  the user
		// can resize it in the editor if they wish.
		$max_width = intval(get_option('large_size_w'));
		$max_height = intval(get_option('large_size_h'));
		if ( intval($content_width) > 0 )
			$max_width = min( intval($content_width), $max_width );
	}
	// $size == 'full' has no constraint
	else {
		$max_width = $width;
		$max_height = $height;
	}

	list( $max_width, $max_height ) = apply_filters( 'editor_max_image_size', array( $max_width, $max_height ), $size );
	
	return wp_constrain_dimensions( $width, $height, $max_width, $max_height );
}

/**
 * Retrieve width and height attributes using given width and height values.
 *
 * Both attributes are required in the sense that both parameters must have a
 * value, but are optional in that if you set them to false or null, then they
 * will not be added to the returned string.
 *
 * You can set the value using a string, but it will only take numeric values.
 * If you wish to put 'px' after the numbers, then it will be stripped out of
 * the return.
 *
 * @since 2.5.0
 *
 * @param int|string $width Optional. Width attribute value.
 * @param int|string $height Optional. Height attribute value.
 * @return string HTML attributes for width and, or height.
 */
function image_hwstring($width, $height) {
	$out = '';
	if ($width)
		$out .= 'width="'.intval($width).'" ';
	if ($height)
		$out .= 'height="'.intval($height).'" ';
	return $out;
}

/**
 * Scale an image to fit a particular size (such as 'thumb' or 'medium').
 *
 * Array with image url, width, height, and whether is intermediate size, in
 * that order is returned on success is returned. $is_intermediate is true if
 * $url is a resized image, false if it is the original.
 *
 * The URL might be the original image, or it might be a resized version. This
 * function won't create a new resized copy, it will just return an already
 * resized one if it exists.
 *
 * A plugin may use the 'image_downsize' filter to hook into and offer image
 * resizing services for images. The hook must return an array with the same
 * elements that are returned in the function. The first element being the URL
 * to the new image that was resized.
 *
 * @since 2.5.0
 * @uses apply_filters() Calls 'image_downsize' on $id and $size to provide
 *		resize services.
 *
 * @param int $id Attachment ID for image.
 * @param string $size Optional, default is 'medium'. Size of image, can be 'thumbnail'.
 * @return bool|array False on failure, array on success.
 */
function image_downsize($id, $size = 'medium') {

	if ( !wp_attachment_is_image($id) )
		return false;

	$img_url = wp_get_attachment_url($id);
	$meta = wp_get_attachment_metadata($id);
	$width = $height = 0;
	$is_intermediate = false;

	// plugins can use this to provide resize services
	if ( $out = apply_filters('image_downsize', false, $id, $size) )
		return $out;

	// try for a new style intermediate size
	if ( $intermediate = image_get_intermediate_size($id, $size) ) {
		$img_url = str_replace(basename($img_url), $intermediate['file'], $img_url);
		$width = $intermediate['width'];
		$height = $intermediate['height'];
		$is_intermediate = true;
	}
	elseif ( $size == 'thumbnail' ) {
		// fall back to the old thumbnail
		if ( ($thumb_file = wp_get_attachment_thumb_file($id)) && $info = getimagesize($thumb_file) ) {
			$img_url = str_replace(basename($img_url), basename($thumb_file), $img_url);
			$width = $info[0];
			$height = $info[1];
			$is_intermediate = true;
		}
	}
	if ( !$width && !$height && isset($meta['width'], $meta['height']) ) {
		// any other type: use the real image
		$width = $meta['width'];
		$height = $meta['height'];
	}
	
	if ( $img_url) {
		// we have the actual image size, but might need to further constrain it if content_width is narrower
		list( $width, $height ) = image_constrain_size_for_editor( $width, $height, $size );

		return array( $img_url, $width, $height, $is_intermediate );
	}
	return false;

}

/**
 * An <img src /> tag for an image attachment, scaling it down if requested.
 *
 * The filter 'get_image_tag_class' allows for changing the class name for the
 * image without having to use regular expressions on the HTML content. The
 * parameters are: what WordPress will use for the class, the Attachment ID,
 * image align value, and the size the image should be.
 *
 * The second filter 'get_image_tag' has the HTML content, which can then be
 * further manipulated by a plugin to change all attribute values and even HTML
 * content.
 *
 * @since 2.5.0
 *
 * @uses apply_filters() The 'get_image_tag_class' filter is the IMG element
 *		class attribute.
 * @uses apply_filters() The 'get_image_tag' filter is the full IMG element with
 *		all attributes.
 *
 * @param int $id Attachment ID.
 * @param string $alt Image Description for the alt attribute.
 * @param string $title Image Description for the title attribute.
 * @param string $align Part of the class name for aligning the image.
 * @param string $size Optional. Default is 'medium'.
 * @return string HTML IMG element for given image attachment
 */
function get_image_tag($id, $alt, $title, $align, $size='medium') {

	list( $img_src, $width, $height ) = image_downsize($id, $size);
	$hwstring = image_hwstring($width, $height);

	$class = 'align'.attribute_escape($align).' size-'.attribute_escape($size).' wp-image-'.$id;
	$class = apply_filters('get_image_tag_class', $class, $id, $align, $size);

	$html = '<img src="'.attribute_escape($img_src).'" alt="'.attribute_escape($alt).'" title="'.attribute_escape($title).'" '.$hwstring.'class="'.$class.'" />';

	$html = apply_filters( 'get_image_tag', $html, $id, $alt, $title, $align, $size );

	return $html;
}

/**
 * Calculates the new dimentions for a downsampled image.
 *
 * Same as {@link wp_shrink_dimensions()}, except the max parameters are
 * optional. If either width or height are empty, no constraint is applied on
 * that dimension.
 *
 * @since 2.5.0
 *
 * @param int $current_width Current width of the image.
 * @param int $current_height Current height of the image.
 * @param int $max_width Optional. Maximum wanted width.
 * @param int $max_height Optional. Maximum wanted height.
 * @return array First item is the width, the second item is the height.
 */
function wp_constrain_dimensions( $current_width, $current_height, $max_width=0, $max_height=0 ) {
	if ( !$max_width and !$max_height )
		return array( $current_width, $current_height );

	$width_ratio = $height_ratio = 1.0;

	if ( $max_width > 0 && $current_width > $max_width )
		$width_ratio = $max_width / $current_width;

	if ( $max_height > 0 && $current_height > $max_height )
		$height_ratio = $max_height / $current_height;

	// the smaller ratio is the one we need to fit it to the constraining box
	$ratio = min( $width_ratio, $height_ratio );

	return array( intval($current_width * $ratio), intval($current_height * $ratio) );
}

/**
 * Retrieve calculated resized dimensions for use in imagecopyresampled().
 *
 * Calculate dimensions and coordinates for a resized image that fits within a
 * specified width and height. If $crop is true, the largest matching central
 * portion of the image will be cropped out and resized to the required size.
 *
 * @since 2.5.0
 *
 * @param int $orig_w Original width.
 * @param int $orig_h Original height.
 * @param int $dest_w New width.
 * @param int $dest_h New height.
 * @param bool $crop Optional, default is false. Whether to crop image or resize.
 * @return bool|array False, on failure. Returned array matches parameters for imagecopyresampled() PHP function.
 */
function image_resize_dimensions($orig_w, $orig_h, $dest_w, $dest_h, $crop=false) {

	if ($orig_w <= 0 || $orig_h <= 0)
		return false;
	// at least one of dest_w or dest_h must be specific
	if ($dest_w <= 0 && $dest_h <= 0)
		return false;

	if ( $crop ) {
		// crop the largest possible portion of the original image that we can size to $dest_w x $dest_h
		$aspect_ratio = $orig_w / $orig_h;
		$new_w = min($dest_w, $orig_w);
		$new_h = min($dest_h, $orig_h);
		if (!$new_w) {
			$new_w = intval($new_h * $aspect_ratio);
		}
		if (!$new_h) {
			$new_h = intval($new_w / $aspect_ratio);
		}

		$size_ratio = max($new_w / $orig_w, $new_h / $orig_h);

		$crop_w = ceil($new_w / $size_ratio);
		$crop_h = ceil($new_h / $size_ratio);

		$s_x = floor(($orig_w - $crop_w)/2);
		$s_y = floor(($orig_h - $crop_h)/2);
	}
	else {
		// don't crop, just resize using $dest_w x $dest_h as a maximum bounding box
		$crop_w = $orig_w;
		$crop_h = $orig_h;

		$s_x = 0;
		$s_y = 0;

		list( $new_w, $new_h ) = wp_constrain_dimensions( $orig_w, $orig_h, $dest_w, $dest_h );
	}

	// if the resulting image would be the same size or larger we don't want to resize it
	if ($new_w >= $orig_w && $new_h >= $orig_h)
		return false;

	// the return array matches the parameters to imagecopyresampled()
	// int dst_x, int dst_y, int src_x, int src_y, int dst_w, int dst_h, int src_w, int src_h
	return array(0, 0, $s_x, $s_y, $new_w, $new_h, $crop_w, $crop_h);

}

/**
 * Scale down an image to fit a particular size and save a new copy of the image.
 *
 * The PNG transparency will be preserved using the function, as well as the
 * image type. If the file going in is PNG, then the resized image is going to
 * be PNG. The only supported image types are PNG, GIF, and JPEG.
 *
 * Some functionality requires API to exist, so some PHP version may lose out
 * support. This is not the fault of WordPress (where functionality is
 * downgraded, not actual defects), but of your PHP version.
 *
 * @since 2.5.0
 *
 * @param string $file Image file path.
 * @param int $max_w Maximum width to resize to.
 * @param int $max_h Maximum height to resize to.
 * @param bool $crop Optional. Whether to crop image or resize.
 * @param string $suffix Optional. File Suffix.
 * @param string $dest_path Optional. New image file path.
 * @param int $jpeg_quality Optional, default is 90. Image quality percentage.
 * @return mixed WP_Error on failure. String with new destination path. Array of dimensions from {@link image_resize_dimensions()}
 */
function image_resize( $file, $max_w, $max_h, $crop=false, $suffix=null, $dest_path=null, $jpeg_quality=90) {

	$image = wp_load_image( $file );
	if ( !is_resource( $image ) )
		return new WP_Error('error_loading_image', $image);

	list($orig_w, $orig_h, $orig_type) = getimagesize( $file );
	$dims = image_resize_dimensions($orig_w, $orig_h, $max_w, $max_h, $crop);
	if (!$dims)
		return $dims;
	list($dst_x, $dst_y, $src_x, $src_y, $dst_w, $dst_h, $src_w, $src_h) = $dims;

	$newimage = imagecreatetruecolor( $dst_w, $dst_h);

	// preserve PNG transparency
	if ( IMAGETYPE_PNG == $orig_type && function_exists( 'imagealphablending' ) && function_exists( 'imagesavealpha' ) ) {
		imagealphablending( $newimage, false);
		imagesavealpha( $newimage, true);
	}

	imagecopyresampled( $newimage, $image, $dst_x, $dst_y, $src_x, $src_y, $dst_w, $dst_h, $src_w, $src_h);

	// we don't need the original in memory anymore
	imagedestroy( $image );

	// $suffix will be appended to the destination filename, just before the extension
	if ( !$suffix )
		$suffix = "{$dst_w}x{$dst_h}";

	$info = pathinfo($file);
	$dir = $info['dirname'];
	$ext = $info['extension'];
	$name = basename($file, ".{$ext}");
	if ( !is_null($dest_path) and $_dest_path = realpath($dest_path) )
		$dir = $_dest_path;
	$destfilename = "{$dir}/{$name}-{$suffix}.{$ext}";

	if ( $orig_type == IMAGETYPE_GIF ) {
		if (!imagegif( $newimage, $destfilename ) )
			return new WP_Error('resize_path_invalid', __( 'Resize path invalid' ));
	}
	elseif ( $orig_type == IMAGETYPE_PNG ) {
		if (!imagepng( $newimage, $destfilename ) )
			return new WP_Error('resize_path_invalid', __( 'Resize path invalid' ));
	}
	else {
		// all other formats are converted to jpg
		$destfilename = "{$dir}/{$name}-{$suffix}.jpg";
		if (!imagejpeg( $newimage, $destfilename, apply_filters( 'jpeg_quality', $jpeg_quality ) ) )
			return new WP_Error('resize_path_invalid', __( 'Resize path invalid' ));
	}

	imagedestroy( $newimage );

	// Set correct file permissions
	$stat = stat( dirname( $destfilename ));
	$perms = $stat['mode'] & 0000666; //same permissions as parent folder, strip off the executable bits
	@ chmod( $destfilename, $perms );

	return $destfilename;
}

/**
 * Resize an image to make a thumbnail or intermediate size.
 *
 * The returned array has the file size, the image width, and image height. The
 * filter 'image_make_intermediate_size' can be used to hook in and change the
 * values of the returned array. The only parameter is the resized file path.
 *
 * @since 2.5.0
 *
 * @param string $file File path.
 * @param int $width Image width.
 * @param int $height Image height.
 * @param bool $crop Optional, default is false. Whether to crop image to specified height and width or resize.
 * @return bool|array False, if no image was created. Metadata array on success.
 */
function image_make_intermediate_size($file, $width, $height, $crop=false) {
	if ( $width || $height ) {
		$resized_file = image_resize($file, $width, $height, $crop);
		if ( !is_wp_error($resized_file) && $resized_file && $info = getimagesize($resized_file) ) {
			$resized_file = apply_filters('image_make_intermediate_size', $resized_file);
			return array(
				'file' => basename( $resized_file ),
				'width' => $info[0],
				'height' => $info[1],
			);
		}
	}
	return false;
}

/**
 * Retrieve the image's intermediate size (resized) path, width, and height.
 *
 * The $size parameter can be an array with the width and height respectively.
 * If the size matches the 'sizes' metadata array for width and height, then it
 * will be used. If there is no direct match, then the nearest image size larger
 * than the specified size will be used. If nothing is found, then the function
 * will break out and return false.
 * 
 * The metadata 'sizes' is used for compatible sizes that can be used for the
 * parameter $size value.
 *
 * The url path will be given, when the $size parameter is a string.
 *
 * @since 2.5.0
 *
 * @param int $post_id Attachment ID for image.
 * @param array|string $size Optional, default is 'thumbnail'. Size of image, either array or string.
 * @return bool|array False on failure or array of file path, width, and height on success.
 */
function image_get_intermediate_size($post_id, $size='thumbnail') {
	if ( !is_array( $imagedata = wp_get_attachment_metadata( $post_id ) ) )
		return false;

	// get the best one for a specified set of dimensions
	if ( is_array($size) && !empty($imagedata['sizes']) ) {
		foreach ( $imagedata['sizes'] as $_size => $data ) {
			// already cropped to width or height; so use this size
			if ( ( $data['width'] == $size[0] && $data['height'] <= $size[1] ) || ( $data['height'] == $size[1] && $data['width'] <= $size[0] ) ) {
				$file = $data['file'];
				list($width, $height) = image_constrain_size_for_editor( $data['width'], $data['height'], $size );
				return compact( 'file', 'width', 'height' );
			}
			// add to lookup table: area => size
			$areas[$data['width'] * $data['height']] = $_size;
		}
		if ( !$size || !empty($areas) ) {
			// find for the smallest image not smaller than the desired size
			ksort($areas);
			foreach ( $areas as $_size ) {
				$data = $imagedata['sizes'][$_size];
				if ( $data['width'] >= $size[0] || $data['height'] >= $size[1] ) {
					$file = $data['file'];
					list($width, $height) = image_constrain_size_for_editor( $data['width'], $data['height'], $size );
					return compact( 'file', 'width', 'height' );
				}
			}
		}
	}

	if ( is_array($size) || empty($size) || empty($imagedata['sizes'][$size]) )
		return false;

	$data = $imagedata['sizes'][$size];
	// include the full filesystem path of the intermediate file
	if ( empty($data['path']) && !empty($data['file']) ) {
		$file_url = wp_get_attachment_url($post_id);
		$data['path'] = path_join( dirname($imagedata['file']), $data['file'] );
		$data['url'] = path_join( dirname($file_url), $data['file'] );
	}
	return $data;
}

/**
 * Retrieve an image to represent an attachment.
 *
 * A mime icon for files, thumbnail or intermediate size for images.
 *
 * @since 2.5.0
 *
 * @param int $attachment_id Image attachment ID.
 * @param string $size Optional, default is 'thumbnail'.
 * @param bool $icon Optional, default is false. Whether it is an icon.
 * @return bool|array Returns an array (url, width, height), or false, if no image is available.
 */
function wp_get_attachment_image_src($attachment_id, $size='thumbnail', $icon = false) {

	// get a thumbnail or intermediate image if there is one
	if ( $image = image_downsize($attachment_id, $size) )
		return $image;

	if ( $icon && $src = wp_mime_type_icon($attachment_id) ) {
		$icon_dir = apply_filters( 'icon_dir', ABSPATH . WPINC . '/images/crystal' );
		$src_file = $icon_dir . '/' . basename($src);
		@list($width, $height) = getimagesize($src_file);
	}
	if ( $src && $width && $height )
		return array( $src, $width, $height );
	return false;
}

/**
 * Retrieve img HTML content for an image to represent an attachment.
 *
 * @see wp_get_attachment_image_src() Returns img HTML element based on array.
 * @since 2.5.0
 *
 * @param int $attachment_id Image attachment ID.
 * @param string $size Optional, default is 'thumbnail'.
 * @param bool $icon Optional, default is false. Whether it is an icon.
 * @return string HTML img element or empty string on failure.
 */
function wp_get_attachment_image($attachment_id, $size = 'thumbnail', $icon = false) {

	$html = '';
	$image = wp_get_attachment_image_src($attachment_id, $size, $icon);
	if ( $image ) {
		list($src, $width, $height) = $image;
		$hwstring = image_hwstring($width, $height);
		if ( is_array($size) )
			$size = join('x', $size);
		$html = '<img src="'.attribute_escape($src).'" '.$hwstring.'class="attachment-'.attribute_escape($size).'" alt="" />';
	}

	return $html;
}

add_shortcode('wp_caption', 'img_caption_shortcode');
add_shortcode('caption', 'img_caption_shortcode');

/**
 * The Caption shortcode.
 *
 * Allows a plugin to replace the content that would otherwise be returned. The
 * filter is 'img_caption_shortcode' and passes an empty string, the attr
 * parameter and the content parameter values.
 *
 * The supported attributes for the shortcode are 'id', 'align', 'width', and
 * 'caption'.
 *
 * @since 2.6.0
 *
 * @param array $attr Attributes attributed to the shortcode.
 * @param string $content Optional. Shortcode content.
 * @return string
 */
function img_caption_shortcode($attr, $content = null) {

	// Allow plugins/themes to override the default caption template.
	$output = apply_filters('img_caption_shortcode', '', $attr, $content);
	if ( $output != '' )
		return $output;

	extract(shortcode_atts(array(
		'id'	=> '',
		'align'	=> 'alignnone',
		'width'	=> '',
		'caption' => ''
	), $attr));

	if ( 1 > (int) $width || empty($caption) )
		return $content;

	if ( $id ) $id = 'id="' . $id . '" ';

	return '<div ' . $id . 'class="wp-caption ' . $align . '" style="width: ' . (10 + (int) $width) . 'px">'
	. $content . '<p class="wp-caption-text">' . $caption . '</p></div>';
}

add_shortcode('gallery', 'gallery_shortcode');

/**
 * The Gallery shortcode.
 *
 * This implements the functionality of the Gallery Shortcode for displaying
 * WordPress images on a post.
 *
 * @since 2.5.0
 *
 * @param array $attr Attributes attributed to the shortcode.
 * @return string HTML content to display gallery.
 */
function gallery_shortcode($attr) {
	global $post;

	// Allow plugins/themes to override the default gallery template.
	$output = apply_filters('post_gallery', '', $attr);
	if ( $output != '' )
		return $output;

	// We're trusting author input, so let's at least make sure it looks like a valid orderby statement
	if ( isset( $attr['orderby'] ) ) {
		$attr['orderby'] = sanitize_sql_orderby( $attr['orderby'] );
		if ( !$attr['orderby'] )
			unset( $attr['orderby'] );
	}

	extract(shortcode_atts(array(
		'order'      => 'ASC',
		'orderby'    => 'menu_order ID',
		'id'         => $post->ID,
		'itemtag'    => 'dl',
		'icontag'    => 'dt',
		'captiontag' => 'dd',
		'columns'    => 3,
		'size'       => 'thumbnail',
	), $attr));

	$id = intval($id);
	$attachments = get_children( array('post_parent' => $id, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );

	if ( empty($attachments) )
		return '';

	if ( is_feed() ) {
		$output = "\n";
		foreach ( $attachments as $id => $attachment )
			$output .= wp_get_attachment_link($id, $size, true) . "\n";
		return $output;
	}

	$itemtag = tag_escape($itemtag);
	$captiontag = tag_escape($captiontag);
	$columns = intval($columns);
	$itemwidth = $columns > 0 ? floor(100/$columns) : 100;

	$output = apply_filters('gallery_style', "
		<style type='text/css'>
			.gallery {
				margin: auto;
			}
			.gallery-item {
				float: left;
				margin-top: 10px;
				text-align: center;
				width: {$itemwidth}%;			}
			.gallery img {
				border: 2px solid #cfcfcf;
			}
			.gallery-caption {
				margin-left: 0;
			}
		</style>
		<!-- see gallery_shortcode() in wp-includes/media.php -->
		<div class='gallery'>");

	$i = 0;
	foreach ( $attachments as $id => $attachment ) {
		$link = wp_get_attachment_link($id, $size, true);
		$output .= "<{$itemtag} class='gallery-item'>";
		$output .= "
			<{$icontag} class='gallery-icon'>
				$link
			</{$icontag}>";
		if ( $captiontag && trim($attachment->post_excerpt) ) {
			$output .= "
				<{$captiontag} class='gallery-caption'>
				{$attachment->post_excerpt}
				</{$captiontag}>";
		}
		$output .= "</{$itemtag}>";
		if ( $columns > 0 && ++$i % $columns == 0 )
			$output .= '<br style="clear: both" />';
	}

	$output .= "
			<br style='clear: both;' />
		</div>\n";

	return $output;
}

/**
 * Display previous image link that has the same post parent.
 *
 * @since 2.5.0
 */
function previous_image_link() {
	adjacent_image_link(true);
}

/**
 * Display next image link that has the same post parent.
 *
 * @since 2.5.0
 */
function next_image_link() {
	adjacent_image_link(false);
}

/**
 * Display next or previous image link that has the same post parent.
 *
 * Retrieves the current attachment object from the $post global.
 *
 * @since 2.5.0
 *
 * @param bool $prev Optional. Default is true to display previous link, true for next.
 */
function adjacent_image_link($prev = true) {
	global $post;
	$post = get_post($post);
	$attachments = array_values(get_children( array('post_parent' => $post->post_parent, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => 'ASC', 'orderby' => 'menu_order ID') ));

	foreach ( $attachments as $k => $attachment )
		if ( $attachment->ID == $post->ID )
			break;

	$k = $prev ? $k - 1 : $k + 1;

	if ( isset($attachments[$k]) )
		echo wp_get_attachment_link($attachments[$k]->ID, 'thumbnail', true);
}

/**
 * Retrieve taxonomies attached to the attachment.
 *
 * @since 2.5.0
 *
 * @param int|array|object $attachment Attachment ID, Attachment data array, or Attachment data object.
 * @return array Empty array on failure. List of taxonomies on success.
 */
function get_attachment_taxonomies($attachment) {
	if ( is_int( $attachment ) )
		$attachment = get_post($attachment);
	else if ( is_array($attachment) )
		$attachment = (object) $attachment;

	if ( ! is_object($attachment) )
		return array();

	$filename = basename($attachment->guid);

	$objects = array('attachment');

	if ( false !== strpos($filename, '.') )
		$objects[] = 'attachment:' . substr($filename, strrpos($filename, '.') + 1);
	if ( !empty($attachment->post_mime_type) ) {
		$objects[] = 'attachment:' . $attachment->post_mime_type;
		if ( false !== strpos($attachment->post_mime_type, '/') )
			foreach ( explode('/', $attachment->post_mime_type) as $token )
				if ( !empty($token) )
					$objects[] = "attachment:$token";
	}

	$taxonomies = array();
	foreach ( $objects as $object )
		if ( $taxes = get_object_taxonomies($object) )
			$taxonomies = array_merge($taxonomies, $taxes);

	return array_unique($taxonomies);
}

?>