paste layers one by one, centered

BC-Break
- options `size` and `position` are removed
- option `transparency` is renamed `opacity` to conform to values 0=transparent ; 100=full opaque color

lib/php/rendition-factory/src/Transformer/Image/Imagine/BackgroundFilterLoader.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace Alchemy\RenditionFactory\Transformer\Image\Imagine;
+
+use Imagine\Image\ImageInterface;
+use Imagine\Image\ImagineInterface;
+use Imagine\Image\Point;
+use Liip\ImagineBundle\Imagine\Filter\Loader\LoaderInterface;
+
+class BackgroundFilterLoader implements LoaderInterface
+{
+    public function __construct(protected ImagineInterface $imagine)
+    {
+    }
+
+    public function load(ImageInterface $image, array $options = [])
+    {
+        $background = $image->palette()->color(
+            $options['color'] ?? '#fff',
+            $options['opacity'] ?? 100,
+        );
+        $imageSize = $image->getSize();
+
+        $imageW = $imageSize->getWidth();
+        $imageH = $imageSize->getHeight();
+
+        $canvas = $this->imagine->create($imageSize, $background);
+
+        /**
+         * @var ImageInterface $layer
+         */
+        foreach ($image->layers() as $layer) {
+            $layerSize = $layer->getSize();
+            $layerDW = ($imageW - $layerSize->getWidth()) / 2;
+            $layerDH = ($imageH - $layerSize->getHeight()) / 2;
+            $canvas->paste($layer, new Point($layerDW, $layerDH));
+        }
+
+        return $canvas;
+    }
+}

lib/php/rendition-factory/src/Transformer/Image/Imagine/ImagineFilterFactory.php

@@ -10,7 +10,6 @@
 use Liip\ImagineBundle\Imagine\Filter\FilterConfiguration;
 use Liip\ImagineBundle\Imagine\Filter\FilterManager;
 use Liip\ImagineBundle\Imagine\Filter\Loader\AutoRotateFilterLoader;
-use Liip\ImagineBundle\Imagine\Filter\Loader\BackgroundFilterLoader;
 use Liip\ImagineBundle\Imagine\Filter\Loader\CropFilterLoader;
 use Liip\ImagineBundle\Imagine\Filter\Loader\DownscaleFilterLoader;
 use Liip\ImagineBundle\Imagine\Filter\Loader\FixedFilterLoader;