new image_watermark.module needs some help

Hi community,

For a project of mine I'm in need of watermarked images in the image gallery. After searching and following some related threads there dosn't seem to be any public solid contributed solution out there yet that targets this issue. Nevertheless this feature is searched and desired by some other people and is often needed on professional photographer sites. Although my skills are limeted I thought I'll take a try, get involved, contribute something back to the community, learn, extend my skills and build my first drupal modul.

I noticed that it likely won't be a feature included in image.module because it's invented to be basic and feature less. So the right way to go seems to be a new module named image_watermark.module as a contribution to the image.module. Due to my low skills I've got some basic problems which a moderate developer should laugh about and may help me with ease. So here's what I've managed on my own by now. The following codeblocks are all placed in a file called image_watermark.module.

First I became friend with the form api and build the first basic administrative settings:

• checkbox: to enable/disable the module
• checkbox: to apply watermarks to thumbnails if desired (may be seperated in all from image.module generated sizes)
• textfield: to set the location of the watermark image
• selectbox: to choose where the watermark should be placed on the image (only center center works for now)

// $Id: image_watermark.module,v 0.1 2006/07/07 22:51:51 ak Exp $

/**
* Implementation of hook_help().
*/
function image_watermark_help($section) {
	switch ($section) {
		case 'admin/modules#description':
			return t('Adds watermarks to images. (requires image.module)');
	}
}

/*
* Implementation of hook_settings().
*/
function image_watermark_settings() {
	if (!image_get_toolkit()) {
		drupal_set_message('image_watermark: You must enable an image toolkit for this module to work!', 'error');
	} else {
		$form['image_watermark'] = array(
			'#type' => 'fieldset',
			'#title' => t('Watermark settings')
		);
		$form['image_watermark']['image_watermark_enable'] = array(
			'#type' => 'checkbox',
			'#title' => t('Watermark images'),
			'#default_value' => variable_get('image_watermark_enable', 0),
			'#description' => t('If checked, this will create preview images with watermarks.')
		);
		// TODO
		$form['image_watermark']['image_watermark_thumbs'] = array(
			'#type' => 'checkbox',
			'#title' => t('Watermark thumbs (TODO)'),
			'#default_value' => variable_get('image_watermark_thumbs', 0),
			'#description' => t('If checked, this will watermark thumbnail images as well.')
		);
		$form['image_watermark']['image_watermark_path'] = array(
			'#type' => 'textfield',
			'#title' => t('Watermark path'),
			'#default_value' => variable_get('image_watermark_path', drupal_get_path('module', 'image_watermark').'/watermark.png'),
			'#size' => 60,
			'#description' => t('Path to the watermark image. This path is relative to the drupal base directory.')
		);
		$form['image_watermark']['image_watermark_position'] = array(
			'#type' => 'select',
			'#title' => t('Watermark position'),
			'#default_value' => variable_get('image_watermark_position', 'center center'),
			'#options' => array('center center', 'center left', 'center right', 'top center', 'top left', 'top right', 'bottom center', 'bottom left', 'bottom right'),
			'#description' => t('Watermark position on the image.')
		);
	}
	return $form;
}

First question:

• #1 Can I validate the existance of the watermark file directly in the hook_settings function and how?

Next I implemented the hook_nodeapi. I orientated myselfe by some code of the image_exact.module on using this. Give me a hint if there may be an other or better solution doing this.

• #2 Are all the published images updated automatically with the watermark by using this or is this just triggered for new uploaded images and what are the right hooks for both approaches? (both may seem desireable to me, could be implemented as either/or option)

/*
* Implementation of hook_nodeapi(&$node, $op, $teaser = NULL, $page = NULL)
*/
function image_watermark_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {
	if ($node->type == 'image' && $op == 'validate' && variable_get('image_watermark_enable', 1)) {
		$source = file_create_path($node->images['_original']);
		$destination = file_create_path($node->images['preview']);
		$watermarkfile = variable_get('image_watermark_path', drupal_get_path('module', 'image_watermark').'/watermark.png');
		if (file_exists($watermarkfile)) {
			// TODO: How to save the returned image?
			//$newimage = image_watermark_add($destination, $watermarkfile);
			image_watermark_add($destination, $watermarkfile);
		} else {
			// TODO: Can this be validatet in the settings itselve?
			drupal_set_message('image_watermark: Watermark file does not exist.', 'error');
		}
	}
}

Next I found and took some code out of the filerequest.module to create the new merged image out of the uploaded image and the watermark image. This code works great as is and is cool because it supports all file extentions and even 24 bit .png's correctly. But still here my main but simple problem occurs.

/*
  Source of this routine:
  http://www.php.net/manual/en/function.imagecopymerge.php

  // TODO: Check this section below, mostly based on filerequest.module script.
*/

// if set upsample pallet images, produces better results
define("UPSAMPLE_PALLET", true);
// if set to true downsample the watermarked image to the original format, 
// otherwise it will be converted to a jpg
define("DOWNSAMPLE_TO_ORIGIN", true); 

function image_watermark_add($sourcefile, $watermarkfile) {
	// $sourcefile = Filename of the picture to be watermarked.
	// $watermarkfile = Filename of the 24-bit PNG watermark file.
	
	//Get the resource ids of the pictures
	$watermarkfile_id = imagecreatefrompng($watermarkfile);
	
	imageAlphaBlending($watermarkfile_id, false);
	imageSaveAlpha($watermarkfile_id, true);
	
	$fileType = getimagesize($sourcefile);
	
	switch($fileType[2]) {
		case 1:
			$sourcefile_id = imagecreatefromgif($sourcefile);
			break;
		
		case 2:
			$sourcefile_id = imagecreatefromjpeg($sourcefile);
			break;
		
		case 3:
			$sourcefile_id = imagecreatefrompng($sourcefile);
			break;
	}
	
	// Get the sizes of both pix 
	$sourcefile_width = imageSX($sourcefile_id);
	$sourcefile_height = imageSY($sourcefile_id);
	$watermarkfile_width = imageSX($watermarkfile_id);
	$watermarkfile_height = imageSY($watermarkfile_id);
	
	// Center the watermark for now
	$dest_x = ( $sourcefile_width / 2 ) - ( $watermarkfile_width / 2 );
	$dest_y = ( $sourcefile_height / 2 ) - ( $watermarkfile_height / 2 );
	
	$upsampled = 0;
	
	// if a gif, we have to upsample it to a truecolor image
	if(UPSAMPLE_PALLET && !imageistruecolor($sourcefile_id)) {
	
		// create an empty truecolor container
		$tempimage = imagecreatetruecolor($sourcefile_width, $sourcefile_height);
		
		$upsampled = imagecolorstotal($sourcefile_id);
		
		// copy the 8-bit gif into the truecolor image
		imagecopy($tempimage, $sourcefile_id, 0, 0, 0, 0, $sourcefile_width, $sourcefile_height);
		imagedestroy($sourcefile_id);
		
		// copy the source_id int
		$sourcefile_id = $tempimage;
	}
	
	imagecopy($sourcefile_id, $watermarkfile_id, $dest_x, $dest_y, 0, 0, $watermarkfile_width, $watermarkfile_height);
	
	if ($upsampled) {
		if (DOWNSAMPLE_TO_ORIGIN && function_exists('imagetruecolortopalette')) {
			__fr_imagetruecolortopalette_ex($sourcefile_id, true, 256);
		} else {
			$fileType[2] = 2; // force to JPEG to reduce size
		}
	}
	
	//Create a jpeg out of the modified picture
	switch($fileType[2]) {
	
		// remember we don't need gif any more, so we use only png or jpeg.
		// See the upsaple code immediately above to see how we handle gifs
		case 3:
			header("Content-type: image/png");
			imagepng($sourcefile_id);
			break;
		
		case 1:
			if (imagetypes() & IMG_GIF) {
			  header("Content-type: image/gif");
			  imagegif($sourcefile_id);
			  break;
			}
		
		default:
			header("Content-type: image/jpg");
			imagejpeg($sourcefile_id);
	}

        // TODO: How to manage this?
	//image_resize($sourcefile_id, $sourcefile, $sourcefile_width, $sourcefile_height);
	
	imagedestroy($sourcefile_id);
	imagedestroy($watermarkfile_id);
}

// litle helper function
// only applies to images other than jpg
// must be renamed latter
function __fr_imagetruecolortopalette_ex( $image, $dither, $ncolors )
{
	if (function_exists('imagecolormatch')) {
		$width = imagesx( $image );
		$height = imagesy( $image );
		$colors_handle = ImageCreateTrueColor( $width, $height );
		ImageCopyMerge( $colors_handle, $image, 0, 0, 0, 0, $width, $height, 100 );
	}
	ImageTrueColorToPalette( $image, $dither, $ncolors );
	if (function_exists('imagecolormatch')) {
		ImageColorMatch( $colors_handle, $image );
		ImageDestroy( $colors_handle );
	}
}

So far, so good. If you now submit an image node you get an image with your 24 bit transparent watermark.png centered on the uploaded source image. But, thats all you see, just the image, nothing else. As you may noticed at the bottom of the image_watermark_add function there are headers set that result in just seeing the image and not your view/edit page any more.
So here's my third and most importend question:

• #3 How can I save and or overwrite the preview image generated by image.module with my newly generated, watermarked image.

Last but not least a wishlist and posible Roadmap for this module could be:

• asign watermarks per taxonomie (for selected galleries only)
• asign watermarks per node (as fieldset on node/xx/edit page)
• asign watermarks per user (upload watermark on user account page)
• apply different watermarks to different image sizes
• position watermarks individualy with drag&drop js
• .. tune in with some ideas ...

And please help me solve my problem.

Greetings Steven