Fix #217

Author: TijZwa

html5/js/OffscreenDecodeWorker.js

@@ -181,7 +181,8 @@ class WindowDecoder {
           w: packet[4],
           h: packet[5],
         },
-        [packet[7]]
+        // Scroll does not hold a transferable type
+        coding == "scroll" ? [] : [packet[7]]
       );
     }
   }

html5/js/PaintWorker.js

@@ -70,6 +70,7 @@ class XpraPaintWorker {
       context.drawImage(image, x, y, width, height);
       this.paint_box(coding, context, x, y, width, height);
     } else if (coding == "scroll") {
+      let canvas = this.offscreen_canvas.get(wid);
       context.imageSmoothingEnabled = false;
       for (let index = 0, stop = image.length; index < stop; ++index) {
         const scroll_data = image[index];
@@ -80,7 +81,7 @@ class XpraPaintWorker {
         const xdelta = scroll_data[4];
         const ydelta = scroll_data[5];
         context.drawImage(
-          this.canvas,
+          canvas,
           sx,
           sy,
           sw,