Print Preview: Make generate draft mode work again.

chrome/browser/resources/print_preview/preview_generator.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('print_preview', function() {
   'use strict';
 
   /**
    * Interface to the Chromium print preview generator.
    * @param {!print_preview.DestinationStore} destinationStore Used to get the
@@ skipping 40 matching lines @@
 
     /**
      * ID of current in-flight request. Requests that do not share this ID will
      * be ignored.
      * @type {number}
      * @private
      */
     this.inFlightRequestId_ = -1;
 
     /**
+     * Whether the current in flight request requires generating draft pages for
+     * print preview. This is true only for modifiable documents when the print
+     * settings has changed sufficiently to require re-rendering.
+     * @type {boolean}

[dpapad, 2017/04/22 01:32:49]

Nit: @private {boolean}

[Lei Zhang, 2017/04/28 01:38:08]

Done.

+     * @private
+     */
+    this.generateDraft_ = false;
+
+    /**
      * Media size to generate preview with. {@code null} indicates default size.
      * @type {cp.cdd.MediaSizeTicketItem}
      * @private
      */
     this.mediaSize_ = null;
 
     /**
      * Whether the previews are being generated in landscape mode.
      * @type {boolean}
      * @private
@@ skipping 95 matching lines @@
      * Request that new preview be generated. A preview request will not be
      * generated if the print ticket has not changed sufficiently.
      * @return {boolean} Whether a new preview was actually requested.
      */
     requestPreview: function() {
       if (!this.printTicketStore_.isTicketValidForPreview() ||
           !this.printTicketStore_.isInitialized ||
           !this.destinationStore_.selectedDestination) {
         return false;
       }
-      if (!this.hasPreviewChanged_()) {
+      var previewChanged = this.hasPreviewChanged_();
+      if (!previewChanged && !this.hasPreviewPageRangeChanged_()) {
         // Changes to these ticket items might not trigger a new preview, but
         // they still need to be recorded.
         this.marginsType_ = this.printTicketStore_.marginsType.getValue();
         return false;
       }
       this.mediaSize_ = this.printTicketStore_.mediaSize.getValue();
       this.isLandscapeEnabled_ = this.printTicketStore_.landscape.getValue();
       this.isHeaderFooterEnabled_ =
           this.printTicketStore_.headerFooter.getValue();
       this.colorValue_ = this.printTicketStore_.color.getValue();
       this.isFitToPageEnabled_ = this.printTicketStore_.fitToPage.getValue();
       this.scalingValue_ = this.printTicketStore_.scaling.getValueAsNumber();
       this.pageRanges_ = this.printTicketStore_.pageRange.getPageRanges();
       this.marginsType_ = this.printTicketStore_.marginsType.getValue();
       this.isCssBackgroundEnabled_ =
           this.printTicketStore_.cssBackground.getValue();
       this.isSelectionOnlyEnabled_ =
           this.printTicketStore_.selectionOnly.getValue();
       this.selectedDestination_ = this.destinationStore_.selectedDestination;
 
       this.inFlightRequestId_++;
+      this.generateDraft_ = this.documentInfo_.isModifiable && previewChanged;
       this.nativeLayer_.startGetPreview(
           this.destinationStore_.selectedDestination,
           this.printTicketStore_,
           this.documentInfo_,
+          this.generateDraft_,
           this.inFlightRequestId_);
       return true;
     },
 
     /** Removes all event listeners that the preview generator has attached. */
     removeEventListeners: function() {
       this.tracker_.removeAll();
     },
 
     /**
@@ skipping 54 matching lines @@
           PreviewGenerator.EventType.PREVIEW_START);
       if (!this.documentInfo_.isModifiable) {
         index = -1;
       }
       previewStartEvent.previewUrl = 'chrome://print/' +
           previewUid.toString() + '/' + index + '/print.pdf';
       this.dispatchEvent(previewStartEvent);
     },
 
     /**
-     * @return {boolean} Whether the print ticket has changed sufficiently to
-     *     determine whether a new preview request should be issued.
+     * @return {boolean} Whether the print ticket, excluding the page range, has
+     *     changed sufficiently to determine whether a new preview request
+     *     should be issued.
      * @private
      */
     hasPreviewChanged_: function() {
       var ticketStore = this.printTicketStore_;
       return this.inFlightRequestId_ == -1 ||
           !ticketStore.mediaSize.isValueEqual(this.mediaSize_) ||
           !ticketStore.landscape.isValueEqual(this.isLandscapeEnabled_) ||
           !ticketStore.headerFooter.isValueEqual(this.isHeaderFooterEnabled_) ||
           !ticketStore.color.isValueEqual(this.colorValue_) ||
           !ticketStore.scaling.isValueEqual(this.scalingValue_) ||
           !ticketStore.fitToPage.isValueEqual(this.isFitToPageEnabled_) ||
-          this.pageRanges_ == null ||
-          !areRangesEqual(ticketStore.pageRange.getPageRanges(),
-                          this.pageRanges_) ||
           (!ticketStore.marginsType.isValueEqual(this.marginsType_) &&
               !ticketStore.marginsType.isValueEqual(
                   print_preview.ticket_items.MarginsType.Value.CUSTOM)) ||
           (ticketStore.marginsType.isValueEqual(
               print_preview.ticket_items.MarginsType.Value.CUSTOM) &&
               !ticketStore.customMargins.isValueEqual(
                   this.documentInfo_.margins)) ||
           !ticketStore.cssBackground.isValueEqual(
               this.isCssBackgroundEnabled_) ||
           !ticketStore.selectionOnly.isValueEqual(
               this.isSelectionOnlyEnabled_) ||
           (this.selectedDestination_ !=
               this.destinationStore_.selectedDestination);
     },
 
     /**
+     * @return {boolean} Whether the page range in the print ticket has changed.
+     * @private
+     */
+    hasPreviewPageRangeChanged_: function() {
+      return this.pageRanges_ == null ||
+          !areRangesEqual(this.printTicketStore_.pageRange.getPageRanges(),
+              this.pageRanges_);

[dpapad, 2017/04/22 01:32:49]

Nit (optional): There used to be a so called "box rule" in one of our
styleguides, but can't find it anymore. Meaning that one should be able to draw
a box around a subtree of the code.

!areRangesEqual(
    this.printTicketStore_.pageRange.getPageRanges(),
    this.pageRanges_);

[Lei Zhang, 2017/04/28 01:38:08]

Done.

+    },
+
+    /**
      * Called when the page layout of the document is ready. Always occurs
      * as a result of a preview request.
      * @param {Event} event Contains layout info about the document.
      * @private
      */
     onPageLayoutReady_: function(event) {
       // NOTE: A request ID is not specified, so assuming its for the current
       // in-flight request.
 
       var origin = new print_preview.Coordinate2d(
@@ skipping 62 matching lines @@
     /**
      * Called when the preview generation is complete. Dispatches a
      * DOCUMENT_READY event.
      * @param {Event} event Contains the preview UID and response ID.
      * @private
      */
     onPreviewGenerationDone_: function(event) {
       if (this.inFlightRequestId_ != event.previewResponseId) {
         return; // Ignore old response.
       }
-      // Dispatch a PREVIEW_START event since non-modifiable documents don't
-      // trigger PAGE_READY events.
-      if (!this.documentInfo_.isModifiable) {
+      if (!this.generateDraft_) {
+        // Dispatch a PREVIEW_START event since not generating a draft PDF,
+        // which includes print preview for non-modifiable documents, does not
+        // trigger PAGE_READY events.
         this.dispatchPreviewStartEvent_(event.previewUid, 0);
       }
       cr.dispatchSimpleEvent(this, PreviewGenerator.EventType.DOCUMENT_READY);
     },
 
     /**
      * Called when the preview generation fails.
      * @private
      */
     onPreviewGenerationFail_: function() {
       // NOTE: No request ID is returned from Chromium so its assumed its the
       // current one.
       cr.dispatchSimpleEvent(this, PreviewGenerator.EventType.FAIL);
     }
   };
 
   // Export
   return {
     PreviewGenerator: PreviewGenerator
   };
 });