From ab6cdf102e0154701d4b04ec2597076baa175b5b Mon Sep 17 00:00:00 2001
From: jonw-cogapp <jonw@cogapp.com>
Date: Fri, 21 Apr 2017 18:19:11 +0100
Subject: [PATCH 1/2] prevent unnecessary panBy on canvas-drag in viewer

---
 src/viewer.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/viewer.js b/src/viewer.js
index 7e9f36c3..7a75d6a5 100644
--- a/src/viewer.js
+++ b/src/viewer.js
@@ -2573,7 +2573,9 @@ function onCanvasDrag( event ) {
         if( !this.panVertical ){
             event.delta.y = 0;
         }
-        this.viewport.panBy( this.viewport.deltaPointsFromPixels( event.delta.negate() ), gestureSettings.flickEnabled );
+        if( event.delta.x !== 0 || event.delta.y !== 0){
+            this.viewport.panBy( this.viewport.deltaPointsFromPixels( event.delta.negate() ), gestureSettings.flickEnabled );
+        }
         if( this.constrainDuringPan ){
             this.viewport.applyConstraints();
         }

From bb229c24d323aaee5a2a9d569198eee928945250 Mon Sep 17 00:00:00 2001
From: superbland <quickxmail@gmail.com>
Date: Mon, 24 Apr 2017 22:47:40 +0100
Subject: [PATCH 2/2] Only apply constraints during an actual drag

---
 src/viewer.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/viewer.js b/src/viewer.js
index 7a75d6a5..ec4c8242 100644
--- a/src/viewer.js
+++ b/src/viewer.js
@@ -2573,11 +2573,11 @@ function onCanvasDrag( event ) {
         if( !this.panVertical ){
             event.delta.y = 0;
         }
-        if( event.delta.x !== 0 || event.delta.y !== 0){
+        if( event.delta.x !== 0 || event.delta.y !== 0 ){
             this.viewport.panBy( this.viewport.deltaPointsFromPixels( event.delta.negate() ), gestureSettings.flickEnabled );
-        }
-        if( this.constrainDuringPan ){
-            this.viewport.applyConstraints();
+            if( this.constrainDuringPan ){
+                this.viewport.applyConstraints();
+            }
         }
     }
 }