Fix #7798: Refactor scratch canvas usage.

Fixes extra canvas create calls.
Fixes unnecessary call of `new DOMCanvasFactory`.
Fixes undefined error of DOMCanvasFactory.
Fixes failures in some of the tests.
Fixes expected behaviour.
Remove unused vars.

src/display/api.js

@@ -61,9 +61,9 @@ var warn = sharedUtil.warn;
 var FontFaceObject = displayFontLoader.FontFaceObject;
 var FontLoader = displayFontLoader.FontLoader;
 var CanvasGraphics = displayCanvas.CanvasGraphics;
-var createScratchCanvas = displayCanvas.createScratchCanvas;
 var Metadata = displayMetadata.Metadata;
 var getDefaultSetting = displayDOMUtils.getDefaultSetting;
+var DOMCanvasFactory = displayDOMUtils.DOMCanvasFactory;
 
 var DEFAULT_RANGE_CHUNK_SIZE = 65536; // 2^16 = 65536
 
@@ -697,6 +697,9 @@ var PDFDocumentProxy = (function PDFDocumentProxyClosure() {
  *                      called each time the rendering is paused.  To continue
  *                      rendering call the function that is the first argument
  *                      to the callback.
+ * @property {Object} canvasFactory - (optional) The factory that will be used
+ *                    when creating canvases. The default value is
+ *                    {DOMCanvasFactory}.
  */
 
 /**
@@ -805,6 +808,7 @@ var PDFPageProxy = (function PDFPageProxyClosure() {
       var renderingIntent = (params.intent === 'print' ? 'print' : 'display');
       var renderInteractiveForms = (params.renderInteractiveForms === true ?
                                     true : /* Default */ false);
+      var canvasFactory = params.canvasFactory || new DOMCanvasFactory();
 
       if (!this.intentStates[renderingIntent]) {
         this.intentStates[renderingIntent] = Object.create(null);
@@ -834,7 +838,8 @@ var PDFPageProxy = (function PDFPageProxyClosure() {
                                                       this.objs,
                                                       this.commonObjs,
                                                       intentState.operatorList,
-                                                      this.pageNumber);
+                                                      this.pageNumber,
+                                                      canvasFactory);
       internalRenderTask.useRequestAnimationFrame = renderingIntent !== 'print';
       if (!intentState.renderTasks) {
         intentState.renderTasks = [];
@@ -1727,6 +1732,12 @@ var WorkerTransport = (function WorkerTransportClosure() {
           return Promise.reject(new Error('Worker was destroyed'));
         }
 
+        if (typeof document === 'undefined') {
+          // Make sure that this code is not executing in node.js, as
+          // it's using DOM image, and there is no library to support that.
+          return Promise.reject(new Error('"document" is not defined.'));
+        }
+
         var imageUrl = data[0];
         var components = data[1];
         if (components !== 3 && components !== 1) {
@@ -1742,7 +1753,9 @@ var WorkerTransport = (function WorkerTransportClosure() {
             var size = width * height;
             var rgbaLength = size * 4;
             var buf = new Uint8Array(size * components);
-            var tmpCanvas = createScratchCanvas(width, height);
+            var tmpCanvas = document.createElement('canvas');
+            tmpCanvas.width = width;
+            tmpCanvas.height = height;
             var tmpCtx = tmpCanvas.getContext('2d');
             tmpCtx.drawImage(img, 0, 0);
             var data = tmpCtx.getImageData(0, 0, width, height).data;
@@ -2030,7 +2043,7 @@ var RenderTask = (function RenderTaskClosure() {
 var InternalRenderTask = (function InternalRenderTaskClosure() {
 
   function InternalRenderTask(callback, params, objs, commonObjs, operatorList,
-                              pageNumber) {
+                              pageNumber, canvasFactory) {
     this.callback = callback;
     this.params = params;
     this.objs = objs;
@@ -2038,6 +2051,7 @@ var InternalRenderTask = (function InternalRenderTaskClosure() {
     this.operatorListIdx = null;
     this.operatorList = operatorList;
     this.pageNumber = pageNumber;
+    this.canvasFactory = canvasFactory;
     this.running = false;
     this.graphicsReadyCallback = null;
     this.graphicsReady = false;
@@ -2068,7 +2082,8 @@ var InternalRenderTask = (function InternalRenderTaskClosure() {
 
       var params = this.params;
       this.gfx = new CanvasGraphics(params.canvasContext, this.commonObjs,
-                                    this.objs, params.imageLayer);
+                                    this.objs, this.canvasFactory,
+                                    params.imageLayer);
 
       this.gfx.beginDrawing(params.transform, params.viewport, transparency);
       this.operatorListIdx = 0;

src/display/canvas.js

@@ -80,13 +80,6 @@ var IsLittleEndianCached = {
   }
 };
 
-function createScratchCanvas(width, height) {
-  var canvas = document.createElement('canvas');
-  canvas.width = width;
-  canvas.height = height;
-  return canvas;
-}
-
 function addContextCurrentTransform(ctx) {
   // If the context doesn't expose a `mozCurrentTransform`, add a JS based one.
   if (!ctx.mozCurrentTransform) {
@@ -204,7 +197,8 @@ function addContextCurrentTransform(ctx) {
 }
 
 var CachedCanvases = (function CachedCanvasesClosure() {
-  function CachedCanvases() {
+  function CachedCanvases(canvasFactory) {
+    this.canvasFactory = canvasFactory;
     this.cache = Object.create(null);
   }
   CachedCanvases.prototype = {
@@ -213,12 +207,11 @@ var CachedCanvases = (function CachedCanvasesClosure() {
       var canvasEntry;
       if (this.cache[id] !== undefined) {
         canvasEntry = this.cache[id];
-        canvasEntry.canvas.width = width;
+        this.canvasFactory.reset(canvasEntry.canvas, width, height);
-        canvasEntry.canvas.height = height;
         // reset canvas transform for emulated mozCurrentTransform, if needed
         canvasEntry.context.setTransform(1, 0, 0, 1, 0, 0);
       } else {
-        var canvas = createScratchCanvas(width, height);
+        var canvas = this.canvasFactory.create(width, height);
         var ctx = canvas.getContext('2d');
         if (trackTransform) {
           addContextCurrentTransform(ctx);
@@ -230,10 +223,7 @@ var CachedCanvases = (function CachedCanvasesClosure() {
     clear: function () {
       for (var id in this.cache) {
         var canvasEntry = this.cache[id];
-        // Zeroing the width and height causes Firefox to release graphics
+        this.canvasFactory.destroy(canvasEntry.canvas);
-        // resources immediately, which can greatly reduce memory consumption.
-        canvasEntry.canvas.width = 0;
-        canvasEntry.canvas.height = 0;
         delete this.cache[id];
       }
     }
@@ -456,7 +446,8 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
   // Defines the number of steps before checking the execution time
   var EXECUTION_STEPS = 10;
 
-  function CanvasGraphics(canvasCtx, commonObjs, objs, imageLayer) {
+  function CanvasGraphics(canvasCtx, commonObjs, objs, canvasFactory,
+                          imageLayer) {
     this.ctx = canvasCtx;
     this.current = new CanvasExtraState();
     this.stateStack = [];
@@ -466,6 +457,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
     this.xobjs = null;
     this.commonObjs = commonObjs;
     this.objs = objs;
+    this.canvasFactory = canvasFactory;
     this.imageLayer = imageLayer;
     this.groupStack = [];
     this.processingType3 = null;
@@ -477,7 +469,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
     this.smaskStack = [];
     this.smaskCounter = 0;
     this.tempSMask = null;
-    this.cachedCanvases = new CachedCanvases();
+    this.cachedCanvases = new CachedCanvases(this.canvasFactory);
     if (canvasCtx) {
       // NOTE: if mozCurrentTransform is polyfilled, then the current state of
       // the transformation must already be set in canvasCtx._transformMatrix.
@@ -1454,7 +1446,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
     get isFontSubpixelAAEnabled() {
       // Checks if anti-aliasing is enabled when scaled text is painted.
       // On Windows GDI scaled fonts looks bad.
-      var ctx = document.createElement('canvas').getContext('2d');
+      var ctx = this.canvasFactory.create(10, 10).getContext('2d');
       ctx.scale(1.5, 1);
       ctx.fillText('I', 0, 10);
       var data = ctx.getImageData(0, 0, 10, 10).data;
@@ -1700,7 +1692,8 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
         var self = this;
         var canvasGraphicsFactory = {
           createCanvasGraphics: function (ctx) {
-            return new CanvasGraphics(ctx, self.commonObjs, self.objs);
+            return new CanvasGraphics(ctx, self.commonObjs, self.objs,
+                                      self.canvasFactory);
           }
         };
         pattern = new TilingPattern(IR, color, this.ctx, canvasGraphicsFactory,
@@ -2320,5 +2313,4 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
 })();
 
 exports.CanvasGraphics = CanvasGraphics;
-exports.createScratchCanvas = createScratchCanvas;
 }));

src/display/dom_utils.js

@@ -26,6 +26,7 @@
   }
 }(this, function (exports, sharedUtil) {
 
+var assert = sharedUtil.assert;
 var removeNullCharacters = sharedUtil.removeNullCharacters;
 var warn = sharedUtil.warn;
 var deprecated = sharedUtil.deprecated;
@@ -33,6 +34,32 @@ var createValidAbsoluteUrl = sharedUtil.createValidAbsoluteUrl;
 
 var DEFAULT_LINK_REL = 'noopener noreferrer nofollow';
 
+function DOMCanvasFactory() {}
+DOMCanvasFactory.prototype = {
+  create: function DOMCanvasFactory_create(width, height) {
+    assert(width > 0 && height > 0, 'invalid canvas size');
+    var canvas = document.createElement('canvas');
+    canvas.width = width;
+    canvas.height = height;
+    return canvas;
+  },
+
+  reset: function DOMCanvasFactory_reset(canvas, width, height) {
+    assert(canvas, 'canvas is not specified');
+    assert(width > 0 && height > 0, 'invalid canvas size');
+    canvas.width = width;
+    canvas.height = height;
+  },
+
+  destroy: function DOMCanvasFactory_destroy(canvas) {
+    assert(canvas, 'canvas is not specified');
+    // Zeroing the width and height cause Firefox to release graphics
+    // resources immediately, which can greatly reduce memory consumption.
+    canvas.width = 0;
+    canvas.height = 0;
+  }
+};
+
 /**
  * Optimised CSS custom property getter/setter.
  * @class
@@ -248,4 +275,5 @@ exports.LinkTarget = LinkTarget;
 exports.hasCanvasTypedArrays = hasCanvasTypedArrays;
 exports.getDefaultSetting = getDefaultSetting;
 exports.DEFAULT_LINK_REL = DEFAULT_LINK_REL;
+exports.DOMCanvasFactory = DOMCanvasFactory;
 }));

src/display/font_loader.js

@@ -216,6 +216,7 @@ if (typeof PDFJSDev === 'undefined' || !PDFJSDev.test('MOZCENTRAL')) {
 
       var i, ii;
 
+      // The temporary canvas is used to determine if fonts are loaded.
       var canvas = document.createElement('canvas');
       canvas.width = 1;
       canvas.height = 1;

src/display/text_layer.js

@@ -186,6 +186,7 @@ var renderTextLayer = (function renderTextLayerClosure() {
       return;
     }
 
+    // The temporary canvas is used to measure text length in the DOM.
     var canvas = document.createElement('canvas');
     if (typeof PDFJSDev === 'undefined' ||
         PDFJSDev.test('FIREFOX || MOZCENTRAL || GENERIC')) {

src/display/webgl.js

@@ -83,6 +83,8 @@ var WebGLUtils = (function WebGLUtilsClosure() {
     if (currentGL) {
       return;
     }
+
+    // The temporary canvas is used in the WebGL context.
     currentCanvas = document.createElement('canvas');
     currentGL = currentCanvas.getContext('webgl',
       { premultipliedalpha: false });