Merge pull request #927 from avandecreme/perf

Optimize sketch canvas clearing and blending.

src/drawer.js

@@ -259,13 +259,17 @@ $.Drawer.prototype = {
         }
     },
 
-    _clear: function ( useSketch ) {
+    _clear: function (useSketch, bounds) {
         if (!this.useCanvas) {
             return;
         }
         var context = this._getContext(useSketch);
+        if (bounds) {
+            context.clearRect(bounds.x, bounds.y, bounds.width, bounds.height);
+        } else {
             var canvas = context.canvas;
             context.clearRect(0, 0, canvas.width, canvas.height);
+        }
     },
 
     /**
@@ -382,21 +386,59 @@ $.Drawer.prototype = {
 
     /**
      * Blends the sketch canvas in the main canvas.
-     * @param {Float} opacity The opacity of the blending.
+     * @param {Object} options The options
-     * @param {Float} [scale=1] The scale at which tiles were drawn on the sketch. Default is 1.
+     * @param {Float} options.opacity The opacity of the blending.
+     * @param {Float} [options.scale=1] The scale at which tiles were drawn on
+     * the sketch. Default is 1.
      * Use scale to draw at a lower scale and then enlarge onto the main canvas.
-     * @param {OpenSeadragon.Point} [translate] A translation vector that was used to draw the tiles
+     * @param {OpenSeadragon.Point} [options.translate] A translation vector
-     * @param {String} [options.compositeOperation] - How the image is composited onto other images; see compositeOperation in {@link OpenSeadragon.Options} for possible values.
+     * that was used to draw the tiles
-     * @returns {undefined}
+     * @param {String} [options.compositeOperation] - How the image is
+     * composited onto other images; see compositeOperation in
+     * {@link OpenSeadragon.Options} for possible values.
+     * @param {OpenSeadragon.Rect} [options.bounds] The part of the sketch
+     * canvas to blend in the main canvas. If specified, options.scale and
+     * options.translate get ignored.
      */
     blendSketch: function(opacity, scale, translate, compositeOperation) {
+        var options = opacity;
+        if (!$.isPlainObject(options)) {
+            options = {
+                opacity: opacity,
+                scale: scale,
+                translate: translate,
+                compositeOperation: compositeOperation
+            };
+        }
         if (!this.useCanvas || !this.sketchCanvas) {
             return;
         }
-        scale = scale || 1;
+        opacity = options.opacity;
+        compositeOperation = options.compositeOperation;
+        var bounds = options.bounds;
+
+        this.context.save();
+        this.context.globalAlpha = opacity;
+        if (compositeOperation) {
+            this.context.globalCompositeOperation = compositeOperation;
+        }
+        if (bounds) {
+            this.context.drawImage(
+                this.sketchCanvas,
+                bounds.x,
+                bounds.y,
+                bounds.width,
+                bounds.height,
+                bounds.x,
+                bounds.y,
+                bounds.width,
+                bounds.height
+            );
+        } else {
+            scale = options.scale || 1;
+            translate = options.translate;
             var position = translate instanceof $.Point ?
-            translate :
+                translate : new $.Point(0, 0);
-            new $.Point(0, 0);
 
             var widthExt = 0;
             var heightExt = 0;
@@ -406,12 +448,6 @@ $.Drawer.prototype = {
                 widthExt = Math.round(widthDiff / 2);
                 heightExt = Math.round(heightDiff / 2);
             }
-
-        this.context.save();
-        this.context.globalAlpha = opacity;
-        if (compositeOperation) {
-            this.context.globalCompositeOperation = compositeOperation;
-        }
             this.context.drawImage(
                 this.sketchCanvas,
                 position.x - widthExt * scale,
@@ -423,6 +459,7 @@ $.Drawer.prototype = {
                 this.canvas.width + 2 * widthExt,
                 this.canvas.height + 2 * heightExt
             );
+        }
         this.context.restore();
     },
 

src/rectangle.js

@@ -367,6 +367,20 @@ $.Rect.prototype = {
             maxY - minY);
     },
 
+    /**
+     * Retrieves the smallest horizontal (degrees=0) rectangle which contains
+     * this rectangle and has integers x, y, width and height
+     * @returns {OpenSeadragon.Rect}
+     */
+    getIntegerBoundingBox: function() {
+        var boundingBox = this.getBoundingBox();
+        var x = Math.floor(boundingBox.x);
+        var y = Math.floor(boundingBox.y);
+        var width = Math.ceil(boundingBox.width + boundingBox.x - x);
+        var height = Math.ceil(boundingBox.height + boundingBox.y - y);
+        return new $.Rect(x, y, width, height);
+    },
+
     /**
      * Provides a string representation of the rectangle which is useful for
      * debugging.

src/tile.js

@@ -195,7 +195,7 @@ $.Tile.prototype = {
 
     // private
     _hasTransparencyChannel: function() {
-        return this.context2D || this.url.match('.png');
+        return !!this.context2D || this.url.match('.png');
     },
 
     /**

src/tiledimage.js

@@ -1448,8 +1448,17 @@ function drawTiles( tiledImage, lastDrawn ) {
             tiledImage._drawer.getCanvasSize(true));
     }
 
+    var bounds;
     if (useSketch) {
-        tiledImage._drawer._clear( true );
+        if (!sketchScale) {
+            // Except when edge smoothing, we only clean the part of the
+            // sketch canvas we are going to use for performance reasons.
+            bounds = tiledImage.viewport.viewportToViewerElementRectangle(
+                tiledImage.getClippedBounds(true))
+                .getIntegerBoundingBox()
+                .times($.pixelDensityRatio);
+        }
+        tiledImage._drawer._clear(true, bounds);
     }
 
     // When scaling, we must rotate only when blending the sketch canvas to avoid
@@ -1532,7 +1541,13 @@ function drawTiles( tiledImage, lastDrawn ) {
         if (offsetForRotation) {
             tiledImage._drawer._offsetForRotation(tiledImage.viewport.degrees, false);
         }
-        tiledImage._drawer.blendSketch(tiledImage.opacity, sketchScale, sketchTranslate, tiledImage.compositeOperation);
+        tiledImage._drawer.blendSketch({
+            opacity: tiledImage.opacity,
+            scale: sketchScale,
+            translate: sketchTranslate,
+            compositeOperation: tiledImage.compositeOperation,
+            bounds: bounds
+        });
         if (offsetForRotation) {
             tiledImage._drawer._restoreRotationChanges(false);
         }