diff --git a/OZprivate/rawJS/OZTreeModule/src/render/renderer.js b/OZprivate/rawJS/OZTreeModule/src/render/renderer.js
index 844c5ee4..38a74aca 100755
--- a/OZprivate/rawJS/OZTreeModule/src/render/renderer.js
+++ b/OZprivate/rawJS/OZTreeModule/src/render/renderer.js
@@ -1,7 +1,6 @@
 import tree_state from '../tree_state';
 import config from '../global_config';
 import {global_button_action} from '../button_manager';
-import {is_on_mobile} from '../util/index';
 /**
  * Renderer controls how to render and routes different shapes to different sub renderers to render
  */
@@ -21,8 +20,6 @@ let temp_context = null;
 let canvas = null;
 let bg_canvas = null;
 let bg_context = null;
-
-let last_draw_by_redraw = true;
   
 function add_controller(_c) {
   controller = _c;
@@ -61,14 +58,10 @@ function refresh(root) {
 
   if (need_refresh()) {
     controller.projection.get_shapes(root, shapes);
-    if (is_on_mobile && tree_state.is_dragging()) {
-      refresh_by_image(shapes);
-    } else {
-      refresh_by_redraw(shapes, context);
-      let end = new Date().getTime();
-      adjust_threshold(end-start);
-      record_view_position();
-    }
+    refresh_by_redraw(shapes, context);
+    let end = new Date().getTime();
+    adjust_threshold(end-start);
+    record_view_position();
     release_shapes(shapes);
   }
 }
@@ -115,40 +108,6 @@ function need_refresh() {
   return false;
 }
 
-function refresh_by_image(shapes) {
-  if (last_draw_by_redraw) {
-    /**
-     ************************************************************************************
-     ***********Solve issue: page turning blank while pinching and then panning***********
-     ************************************************************************************
-     *
-     *
-     * The commented code would possibly result in blank image while pinching and then move.
-     * Because refresh is fired by timer rather than mouse or touch event, front canvas does
-     * not precisely reflect the current tree_state.xp and tree_state.yp.
-     *
-     * Suppose frame 1 is drawn at (0, 0), and last_xp and last_yp is set to (0, 0)
-     * When the xp and yp changed to (2000, 2000) before frame 2, if we draw frame 2 by image, then it 
-     * would first cache frame 1 in background canvas, then draw background canvas onto front canvas
-     * with a shift of (2000, 2000). Clearly, most phones would fail to display any information because (2000, 2000)
-     * is off the screen in frame 1.
-     * .
-     *
-     * In our uncomment code, we draw current view on background canvas by repaint and then reset last_xp and last_yp to (1000,1000).
-     *
-     * Dramatically change in xp and yp while pinching is the real reason behind this issue. In pure panning, xp and yp changes are
-     * so small that we wouldn't worry about shifting the background image and partial blank area is often reasonable and acceptable.
-     */
-    refresh_by_redraw(shapes, bg_context);
-    record_view_position();
-    // bg_context.clearRect(0, 0, tree_state.widthres, tree_state.heightres);
-    // bg_context.drawImage(canvas, 0, 0);
-  }
-  context.clearRect(0,0,tree_state.widthres,tree_state.heightres);
-  context.drawImage(bg_canvas, tree_state.xp - last_xp, tree_state.yp - last_yp);
-  last_draw_by_redraw = false;
-}
-
 function refresh_by_redraw(shapes, _context) {
   _context.clearRect(0,0,tree_state.widthres,tree_state.heightres);
   let length = shapes.length;
@@ -159,7 +118,6 @@ function refresh_by_redraw(shapes, _context) {
      */
     shapes[i].render(_context);
   }
-  last_draw_by_redraw = true;
 }
 
 
diff --git a/OZprivate/rawJS/OZTreeModule/src/util/general.js b/OZprivate/rawJS/OZTreeModule/src/util/general.js
index a7b65d4f..8827ec0d 100755
--- a/OZprivate/rawJS/OZTreeModule/src/util/general.js
+++ b/OZprivate/rawJS/OZTreeModule/src/util/general.js
@@ -9,12 +9,3 @@ export function resolve(obj, str) {
         return prev ? prev[curr] : undefined
     }, obj || self)
 }
-
-export let is_on_mobile = (global && !global.navigator) // i.e. a unit test
-    || navigator.userAgent.match(/Android/i)
-    || navigator.userAgent.match(/webOS/i)
-    || navigator.userAgent.match(/iPhone/i)
-    || navigator.userAgent.match(/iPad/i)
-    || navigator.userAgent.match(/iPod/i)
-    || navigator.userAgent.match(/BlackBerry/i)
-    || navigator.userAgent.match(/Windows Phone/i);