Fix edge smoothing with rotation.

src/drawer.js

@@ -249,8 +249,9 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
                 this.canvas.width = viewportSize.x;
                 this.canvas.height = viewportSize.y;
                 if ( this.sketchCanvas !== null ) {
-                    this.sketchCanvas.width = this.canvas.width;
-                    this.sketchCanvas.height = this.canvas.height;
+                    var sketchCanvasSize = this._calculateSketchCanvasSize();
+                    this.sketchCanvas.width = sketchCanvasSize.x;
+                    this.sketchCanvas.height = sketchCanvasSize.y;
                 }
             }
             this._clear();
@@ -312,8 +313,9 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
         if ( useSketch ) {
             if (this.sketchCanvas === null) {
                 this.sketchCanvas = document.createElement( "canvas" );
-                this.sketchCanvas.width = this.canvas.width;
-                this.sketchCanvas.height = this.canvas.height;
+                var sketchCanvasSize = this._calculateSketchCanvasSize();
+                this.sketchCanvas.width = sketchCanvasSize.x;
+                this.sketchCanvas.height = sketchCanvasSize.y;
                 this.sketchContext = this.sketchCanvas.getContext( "2d" );
             }
             context = this.sketchContext;
@@ -381,18 +383,27 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
             translate :
             new $.Point(0, 0);
 
+        var widthExt = 0;
+        var heightExt = 0;
+        if (translate) {
+            var widthDiff = this.sketchCanvas.width - this.canvas.width;
+            var heightDiff = this.sketchCanvas.height - this.canvas.height;
+            widthExt = Math.round(widthDiff / 2);
+            heightExt = Math.round(heightDiff / 2);
+        }
+
         this.context.save();
         this.context.globalAlpha = opacity;
         this.context.drawImage(
             this.sketchCanvas,
-            position.x,
-            position.y,
-            this.sketchCanvas.width * scale,
-            this.sketchCanvas.height * scale,
-            0,
-            0,
-            this.canvas.width,
-            this.canvas.height
+            position.x - widthExt * scale,
+            position.y - heightExt * scale,
+            (this.canvas.width + 2 * widthExt) * scale,
+            (this.canvas.height  + 2 * heightExt) * scale,
+            -widthExt,
+            -heightExt,
+            this.canvas.width + 2 * widthExt,
+            this.canvas.height + 2 * heightExt
         );
         this.context.restore();
     },
@@ -498,6 +509,16 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
         }
     },
 
+    /**
+     * Get the canvas size
+     * @param {Boolean} sketch If set to true return the size of the sketch canvas
+     * @returns {OpenSeadragon.Point} The size of the canvas
+     */
+    getCanvasSize: function(sketch) {
+        var canvas = this._getContext(sketch).canvas;
+        return new $.Point(canvas.width, canvas.height);
+    },
+
     // private
     _offsetForRotation: function(degrees, useSketch) {
         var cx = this.canvas.width / 2;
@@ -525,6 +546,18 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
             x: viewportSize.x * pixelDensityRatio,
             y: viewportSize.y * pixelDensityRatio
         };
+    },
+
+    // private
+    _calculateSketchCanvasSize: function() {
+        var canvasSize = this._calculateCanvasSize();
+        var sketchCanvasSize = Math.ceil(Math.sqrt(
+            canvasSize.x * canvasSize.x +
+            canvasSize.y * canvasSize.y));
+        return {
+            x: sketchCanvasSize,
+            y: sketchCanvasSize
+        };
     }
 };
 

src/tile.js

@@ -350,11 +350,11 @@ $.Tile.prototype = /** @lends OpenSeadragon.Tile.prototype */{
      * @param {Number} [scale=1] - Scale to be applied to position.
      * @return {OpenSeadragon.Point}
      */
-    getTranslationForEdgeSmoothing: function(scale) {
-        // The translation vector must have positive values, otherwise the image goes a bit off
-        // the sketch canvas to the top and left and we must use negative coordinates to repaint it
-        // to the main canvas. And FF does not like it. It crashes the viewer.
-        return new $.Point(1, 1).minus(
+    getTranslationForEdgeSmoothing: function(scale, canvasSize, sketchCanvasSize) {
+        var sketchCanvasDelta = new $.Point(
+            Math.ceil((sketchCanvasSize.x - canvasSize.x) / 2),
+            Math.ceil((sketchCanvasSize.y - canvasSize.y) / 2));
+        return sketchCanvasDelta.minus(
             this.position
                 .times($.pixelDensityRatio)
                 .times(scale || 1)

src/tiledimage.js

@@ -1324,14 +1324,18 @@ function drawTiles( tiledImage, lastDrawn ) {
         // So we have to composite them at ~100% and scale them up together.
         useSketch = true;
         sketchScale = tile.getScaleForEdgeSmoothing();
-        sketchTranslate = tile.getTranslationForEdgeSmoothing(sketchScale);
+        sketchTranslate = tile.getTranslationForEdgeSmoothing(sketchScale,
+            tiledImage._drawer.getCanvasSize(false),
+            tiledImage._drawer.getCanvasSize(true));
     }
 
     if ( useSketch ) {
         tiledImage._drawer._clear( true );
     }
 
-    if (tiledImage.viewport.degrees !== 0) {
+    // When scaling, we must rotate only when blending the sketch canvas to avoid
+    // interpolation
+    if (tiledImage.viewport.degrees !== 0 && !sketchScale) {
         tiledImage._drawer._offsetForRotation(tiledImage.viewport.degrees, useSketch);
     }
 
@@ -1400,12 +1404,19 @@ function drawTiles( tiledImage, lastDrawn ) {
         tiledImage._drawer.restoreContext( useSketch );
     }
 
-    if (tiledImage.viewport.degrees !== 0) {
+    if (tiledImage.viewport.degrees !== 0 && !sketchScale) {
         tiledImage._drawer._restoreRotationChanges(useSketch);
     }
 
     if (useSketch) {
+        var offsetForRotation = tiledImage.viewport.degrees !== 0 && sketchScale;
+        if (offsetForRotation) {
+            tiledImage._drawer._offsetForRotation(tiledImage.viewport.degrees, false);
+        }
         tiledImage._drawer.blendSketch(tiledImage.opacity, sketchScale, sketchTranslate);
+        if (offsetForRotation) {
+            tiledImage._drawer._restoreRotationChanges(false);
+        }
     }
     drawDebugInfo( tiledImage, lastDrawn );
 }