Fix bug in imagick driver's CropModifier

See: #1426

src/Drivers/Imagick/Modifiers/CropModifier.php

@@ -5,7 +5,6 @@
 namespace Intervention\Image\Drivers\Imagick\Modifiers;
 
 use Imagick;
-use Intervention\Image\Drivers\Imagick\Driver;
 use Intervention\Image\Interfaces\ImageInterface;
 use Intervention\Image\Interfaces\SpecializedInterface;
 use Intervention\Image\Modifiers\CropModifier as GenericCropModifier;
@@ -14,20 +13,30 @@ class CropModifier extends GenericCropModifier implements SpecializedInterface
 {
     public function apply(ImageInterface $image): ImageInterface
     {
-        $crop = $this->crop($image);
+        // decode background color
         $background = $this->driver()->colorProcessor($image->colorspace())->colorToNative(
             $this->driver()->handleInput($this->background)
         );
 
         // create empty container imagick to rebuild core
         $imagick = new Imagick();
+
+        // save resolution to add it later
         $resolution = $image->resolution()->perInch();
 
+        // define position of the image on the new canvas
+        $crop = $this->crop($image);
+        $position = [
+            ($crop->pivot()->x() + $this->offset_x) * -1,
+            ($crop->pivot()->y() + $this->offset_y) * -1,
+        ];
+
         foreach ($image as $frame) {
             // create new frame canvas with modifiers background
             $canvas = new Imagick();
             $canvas->newImage($crop->width(), $crop->height(), $background, 'png');
             $canvas->setImageResolution($resolution->x(), $resolution->y());
+            $canvas->setImageAlphaChannel(Imagick::ALPHACHANNEL_SET); // or ALPHACHANNEL_ACTIVATE?
 
             // set animation details
             if ($image->isAnimated()) {
@@ -36,31 +45,23 @@ public function apply(ImageInterface $image): ImageInterface
                 $canvas->setImageDispose($frame->native()->getImageDispose());
             }
 
-            // place original frame content onto the empty colored frame canvas
-            $canvas->compositeImage(
-                $frame->native(),
-                Imagick::COMPOSITE_DEFAULT,
-                ($crop->pivot()->x() + $this->offset_x) * -1,
-                ($crop->pivot()->y() + $this->offset_y) * -1,
-            );
+            // Make the entire rectangle at the position of the original image
+            // transparent so that we can later place the original on top.
+            // This preserves the transparency of the original and shows
+            // the background color of the modifier in the other areas
+            $clear = new Imagick();
+            $clear->newImage($frame->native()->getImageWidth(), $frame->native()->getImageHeight(), 'black');
+            $canvas->compositeImage($clear, Imagick::COMPOSITE_DSTOUT, ...$position);
 
-            // copy alpha channel if available
-            if ($frame->native()->getImageAlphaChannel()) {
-                $canvas->compositeImage(
-                    $frame->native(),
-                    version_compare(Driver::version(), '7.0.0', '>=') ?
-                        Imagick::COMPOSITE_COPYOPACITY :
-                        Imagick::COMPOSITE_DSTIN,
-                    ($crop->pivot()->x() + $this->offset_x) * -1,
-                    ($crop->pivot()->y() + $this->offset_y) * -1,
-                );
-            }
+            // place original frame content onto the empty colored frame canvas
+            // with the transparent rectangle
+            $canvas->compositeImage($frame->native(), Imagick::COMPOSITE_DEFAULT, ...$position);
 
             // add newly built frame to container imagick
             $imagick->addImage($canvas);
         }
 
-        // replace imagick
+        // replace imagick in the original image
         $image->core()->setNative($imagick);
 
         return $image;