function image_imagemagick_overlay in ImageCache Actions 8

Same name and namespace in other branches

1. 7 image_overlay.inc \image_imagemagick_overlay()

Imagemagick toolkit specific implementation of the image overlay effect.

An underlay should can be created like: -background None -extent 300x250-50-50 under.jpg -compose dst-over -composite

Explanation:

• first enlarge the canvas, making any new part fully transparent.
• placing the "original" image on its requested position
• define the "source" image to IM
• compose the images placing the original over the source

An overlay can be created like: overlay.png -geometry 50x50+100+75 -compose src-over -composite

Explanation:

• define the overlay image to IM
• and define its size and position on the current image
• compose the images placing the original over the source

Please be aware of the limitations of imagemagick libraries out there - the versions distributed on hosted servers (if any) are often several years behind. Using the latest imagemagick release features will make this function unusable in real deployments.

Parameters

stdClass $image: An image object.

stdClass $layer: Image object to be placed over or under the $image image.

int $x: Position of the overlay.

int $y: Position of the overlay.

int $alpha: Transparency of the overlay from 0-100. 0 is totally transparent. 100 (default) is totally opaque.

boolean $reverse: Flag to indicate that the 'overlay' actually goes under the image.

Return value

boolean true on success, false otherwise.

File

./image_overlay.inc, line 147

extension to imageapi, provide an overlay action for blending two layers, preserving transparency.

Code

function image_imagemagick_overlay(stdClass $image, stdClass $layer, $x = 0, $y = 0, $alpha = 100, $reverse = FALSE) {
  $realPath = imagecache_actions_find_file($layer->source);
  if (!$realPath) {
    return FALSE;
  }

  // Reset any gravity settings from earlier effects.
  $image->ops[] = '-gravity None';

  // In imagemagick terms:
  // - $image is the destination (the image being constructed)
  // - $layer is the source (the source of the current operation)
  // Add the layer image to the imagemagick command line.
  // Set the dimensions of the overlay. Use of the scale option means that we
  // need to change the dimensions: always set them, they don't harm when the
  // scale option is not used.
  $sign = $reverse ? -1 : 1;
  $geometry = sprintf('%ux%u%+d%+d', $layer->info['width'], $layer->info['height'], $sign * $x, $sign * $y);
  $compose_operator = $reverse ? 'dst-over' : 'src-over';

  // And compose it with the destination.
  if ($alpha == 100) {

    // Lay one image over the other. The transparency channel of the upper
    // image and/or its dimensions (being smaller than the lower image) will
    // determine what remains visible of the lower image).
    //
    // Note: In explicitly setting a -compose operator we reset/overwrite any
    //   previously set one (former versions could produce erroneous results
    //   in combination with other effects before this one).
    if ($reverse) {

      // Underlay.
      $image->ops[] = '-background';
      $image->ops[] = escapeshellarg('rgba(0,0,0,0)');
      $image->ops[] = "-extent {$geometry}";
      $image->ops[] = escapeshellarg($realPath);
    }
    else {
      $image->ops[] = escapeshellarg($realPath);
      $image->ops[] = "-geometry {$geometry}";
    }
    $image->ops[] = "-compose {$compose_operator} -composite";
  }
  else {

    // Alpha is not 100, so this image effect turns into a blend operation.
    // The alpha determines what percentage of the upper image pixel will be
    // taken. From the lower image pixel, 100 - alpha percent will be taken.
    //
    // Note 1: I'm not sure if and how transparency of one or both images is
    //   used in or after the blend operation.
    // Note 2: As of IM v6.5.3-4 (around june 2009) we can use:
    //   -compose blend -define compose:args=30[,70]
    $image->ops[] = escapeshellarg($realPath);
    $image->ops[] = "-geometry {$geometry}";
    $image->ops[] = "-compose blend -define compose:args={$alpha} -composite";
  }
  return TRUE;
}