Backport asynchronous thumbnail generation from Kabuki.

controllers/GenerateThumbnail.php

@@ -0,0 +1,27 @@
+<?php
+/*****************************************************************************
+ * GenerateThumbnail.php
+ * Contains the asynchronous thumbnail generation controller
+ *
+ * Kabuki CMS (C) 2013-2017, Aaron van Geffen
+ *****************************************************************************/
+
+class GenerateThumbnail extends HTMLController
+{
+	public function __construct()
+	{
+		$asset = Asset::fromId($_GET['id']);
+		if (empty($asset) || !$asset->isImage())
+			throw new NotFoundException('Image not found');
+
+		$image = $asset->getImage();
+		$crop_mode = isset($_GET['mode']) ? $_GET['mode'] : false;
+		$url = $image->getThumbnailUrl($_GET['width'], $_GET['height'], $crop_mode, true, true);
+
+		if ($url)
+		{
+			header('Location: ' . $url);
+			exit;
+		}
+	}
+}