From dd0777141501a462253bcb4bfc698cd77912a49b Mon Sep 17 00:00:00 2001
From: Antoine Vandecreme <ant.vand@gmail.com>
Date: Wed, 22 Apr 2015 18:30:49 -0400
Subject: [PATCH] Fix drawer.clear

---
 src/drawer.js     | 14 +++++++++++---
 src/tiledimage.js |  6 +++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/drawer.js b/src/drawer.js
index 2d39c373..939a8cf0 100644
--- a/src/drawer.js
+++ b/src/drawer.js
@@ -240,7 +240,7 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
     /**
      * Clears the Drawer so it's ready to draw another frame.
      */
-    clear: function( useSketch ) {
+    clear: function() {
         this.canvas.innerHTML = "";
         if ( this.useCanvas ) {
             var viewportSize = this._calculateCanvasSize();
@@ -253,11 +253,19 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
                     this.sketchCanvas.height = this.canvas.height;
                 }
             }
-            this._getContext( useSketch ).clearRect(
-                0, 0, viewportSize.x, viewportSize.y );
+            this._clear();
         }
     },
 
+    _clear: function ( useSketch ) {
+        if ( !this.useCanvas ) {
+            return;
+        }
+        var context = this._getContext( useSketch );
+        var canvas = context.canvas;
+        context.clearRect( 0, 0, canvas.width, canvas.height );
+    },
+
     /**
      * Translates from OpenSeadragon viewer rectangle to drawer rectangle.
      * @param {OpenSeadragon.Rect} rectangle - The rectangle in viewport coordinate system.
diff --git a/src/tiledimage.js b/src/tiledimage.js
index 80515434..faa49cc9 100644
--- a/src/tiledimage.js
+++ b/src/tiledimage.js
@@ -497,12 +497,10 @@ $.extend($.TiledImage.prototype, $.EventSource.prototype, /** @lends OpenSeadrag
 
     /**
      * @param {Number} opacity Opacity the tiled image should be drawn at.
-     * @returns {OpenSeadragon.TiledImage} Chainable
      */
     setOpacity: function(opacity) {
         this.opacity = opacity;
         this._needsDraw = true;
-        return this;
     },
 
     // private
@@ -1178,6 +1176,9 @@ function drawTiles( tiledImage, lastDrawn ) {
         return;
     }
     var useSketch = tiledImage.opacity < 1;
+    if ( useSketch ) {
+        tiledImage._drawer._clear( true );
+    }
 
     var usedClip = false;
     if ( tiledImage._clip ) {
@@ -1234,7 +1235,6 @@ function drawTiles( tiledImage, lastDrawn ) {
 
     if ( useSketch ) {
         tiledImage._drawer.blendSketch( tiledImage.opacity );
-        tiledImage._drawer.clear( true );
     }
     drawDebugInfo( tiledImage, lastDrawn );
 }