From 798e49e4b26ad0191a9e95aaea013a65b9f73e73 Mon Sep 17 00:00:00 2001
From: Takuma Kira <kira@vrs123.com>
Date: Wed, 18 Mar 2020 14:37:45 +0900
Subject: [PATCH] - Add freeupCanvasMemory method on Viewer.destroy method.

---
 src/imagetilesource.js | 12 ++++++++++++
 src/viewer.js          |  4 ++++
 2 files changed, 16 insertions(+)

diff --git a/src/imagetilesource.js b/src/imagetilesource.js
index 375c65d6..d8d2a6d9 100644
--- a/src/imagetilesource.js
+++ b/src/imagetilesource.js
@@ -195,6 +195,18 @@
             }
             return context;
         },
+        /**
+         * Free up canvas memory
+         * (iOS 12 or higher on 2GB RAM device has only 224MB canvas memory,
+         * and Safari keeps canvas until its height and width will be set to 0).
+         * @function
+         */
+        freeupCanvasMemory: function () {
+            for (var i = 0; i < this.levels.length; i++) {
+                this.levels[i].context2D.canvas.height = 0;
+                this.levels[i].context2D.canvas.width = 0;
+            }
+        },
 
         // private
         //
diff --git a/src/viewer.js b/src/viewer.js
index 20e06186..b13483dc 100644
--- a/src/viewer.js
+++ b/src/viewer.js
@@ -742,6 +742,10 @@ $.extend( $.Viewer.prototype, $.EventSource.prototype, $.ControlDock.prototype,
             return;
         }
 
+        if (this.source.freeupCanvasMemory) {
+            this.source.freeupCanvasMemory();
+        }
+
         this.close();
 
         this.clearOverlays();