imagesavealpha() in Writer\AbstractWriter

Author: samsullivan

src/PhpWord/Writer/AbstractWriter.php

@@ -360,6 +360,10 @@ protected function addFilesToPackage(ZipArchive $zip, $elements)
             // Retrive GD image content or get local media
             if (isset($element['isMemImage']) && $element['isMemImage']) {
                 $image = call_user_func($element['createFunction'], $element['source']);
+                if ($element['imageType'] === 'image/png') {
+                    // PNG images need to preserve alpha channel information
+                    imagesavealpha($image, true);
+                }
                 ob_start();
                 call_user_func($element['imageFunction'], $image);
                 $imageContents = ob_get_contents();