Implements PrintBrowser mode.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 72 matching lines @@
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/layout/svg/LayoutSVGRoot.h"
 #include "core/loader/DocumentLoader.h"
 #include "core/loader/FrameLoader.h"
 #include "core/loader/FrameLoaderClient.h"
 #include "core/page/AutoscrollController.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/FocusController.h"
 #include "core/page/FrameTree.h"
 #include "core/page/Page.h"
+#include "core/page/PrintContext.h"
 #include "core/page/scrolling/RootScrollerUtil.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
 #include "core/page/scrolling/TopDocumentRootScrollerController.h"
 #include "core/paint/FramePainter.h"
 #include "core/paint/PaintLayer.h"
 #include "core/paint/PaintTiming.h"
 #include "core/paint/PrePaintTreeWalk.h"
 #include "core/plugins/PluginView.h"
 #include "core/style/ComputedStyle.h"
 #include "core/svg/SVGDocumentExtensions.h"
@@ skipping 35 matching lines @@
 #define CHECK_FOR_DIRTY_LAYOUT(arg) \
   do {                              \
     if (!(arg)) {                   \
       NOTREACHED();                 \
       return false;                 \
     }                               \
   } while (false)
 
 namespace blink {
 
+// A4 Portrait dimensions in pixels
+const int kA4PortraitPageWidth = 595;
+const int kA4PortraitPageHeight = 842;
+
 using namespace HTMLNames;
 
 // The maximum number of updateWidgets iterations that should be done before
 // returning.
 static const unsigned maxUpdateWidgetsIterations = 2;
 static const double resourcePriorityUpdateDelayAfterScroll = 0.250;
 
 static bool s_initialTrackAllPaintInvalidations = false;
 
 FrameView::FrameView(LocalFrame& frame)
@@ skipping 69 matching lines @@
   visitor->trace(m_fragmentAnchor);
   visitor->trace(m_scrollableAreas);
   visitor->trace(m_animatingScrollableAreas);
   visitor->trace(m_autoSizeInfo);
   visitor->trace(m_children);
   visitor->trace(m_viewportScrollableArea);
   visitor->trace(m_visibilityObserver);
   visitor->trace(m_scrollAnchor);
   visitor->trace(m_anchoringAdjustmentQueue);
   visitor->trace(m_scrollbarManager);
+  visitor->trace(m_printContext);
   Widget::trace(visitor);
   ScrollableArea::trace(visitor);
 }
 
 void FrameView::reset() {
   // The compositor throttles the main frame using deferred commits, we can't
   // throttle it here or it seems the root compositor doesn't get setup
   // properly.
   if (RuntimeEnabledFeatures::
           renderingPipelineThrottlingLoadingIframesEnabled())
@@ skipping 2632 matching lines @@
         SourceLocation::capture(m_frame->document()), nullptr);
     m_frame->document()->dispatchErrorEvent(error, NotSharableCrossOrigin);
     // Ensure notifications will get delivered in next cycle.
     if (FrameView* frameView = m_frame->view())
       frameView->scheduleAnimation();
   }
 
   DCHECK(!layoutView()->needsLayout());
 }
 
+void FrameView::dispatchEventsForPrintingOnAllFrames() {
+  DCHECK(m_frame->isMainFrame());
+  for (Frame* currentFrame = m_frame; currentFrame;
+       currentFrame = currentFrame->tree().traverseNext(m_frame)) {
+    if (currentFrame->isLocalFrame())
+      toLocalFrame(currentFrame)->document()->dispatchEventsForPrinting();
+  }
+}
+
+void FrameView::setupPrintContext() {
+  if (!m_frame->document()->printing()) {

[mstensho (USE GERRIT), 2017/02/08 14:32:29]

Could consider an early return here; i.e.:

  if (m_frame->document()->printing())
    return;
  // The rest of the code goes here.

That at least used to be preferred Blink style.

[gozzard, 2017/02/09 04:17:25]

Done.

+    if (!m_printContext)
+      m_printContext = new PrintContext(m_frame);
+    if (m_frame->settings())
+      m_frame->settings()->setShouldPrintBackgrounds(true);
+    FloatRect pageRect(0, 0, kA4PortraitPageWidth, kA4PortraitPageHeight);
+    m_printContext->begin(pageRect.width(), pageRect.height());
+    float height;
+    m_printContext->computePageRects(pageRect, 0, 0, 1.0, height);
+    dispatchEventsForPrintingOnAllFrames();

[pdr., 2017/02/08 06:34:08]

Could you use forAllNonThrottledFrameViews for this?

I.e.,
forAllNonThrottledFrameViews([](FrameView& frameView) {
  frameView.frame().document()->dispatchEventsForPrinting();
});

[gozzard, 2017/02/09 04:17:25]

dispatchEventsForPrinting() ultimately informs some listeners of the media query
change and shuffles any print-related events down to our children. This will not
be run frequently, and seems inadvisable to skip, so we would want to apply this
for throttled FrameViews also. If there existed a forAllFrameViews() variant of
this helper function that may be appropriate, but it would be a simple thin
wrapper around this loop anyway, so I am not inclined to implement such a
helper.

+  }

[pdr., 2017/02/08 06:34:08]

I think this approach can fail to dispatch print events if a subframe has not
yet loaded. For example, if we have a page with an iframe'd ad and we hit this
code before the ad loads, will we fail to ever dispatch the printing event to
the ad? If so, can you add a TODO(gozzard): comment mentioning this?

[gozzard, 2017/02/09 04:17:25]

This appears to be the case. However, I believe this is expected behaviour. The
only endpoints I am aware of for the dispatchEvent() system are javascript
listeners. If the javascript has not yet loaded/executed, it should handle
checking the current state of the page itself, if it is interested. I believe it
is by design that this only notifies existing, registered listeners. Using
printing as an example: It simply triggers any registered MediaQueryList
listeners. The javascript must query for the current MediaQueryList state before
it can even register a listener. If there are any internal events, then they
should follow suit and check the current state on initialization.

+}
+
+void FrameView::clearPrintContext() {
+  if (m_printContext) {

[mstensho (USE GERRIT), 2017/02/08 14:32:29]

Might even consider an early return on !m_printContext here.

[gozzard, 2017/02/09 04:17:26]

Done.

+    m_printContext->end();
+    m_printContext.clear();
+  }
+}
+
 // TODO(leviw): We don't assert lifecycle information from documents in child
 // PluginViews.
 void FrameView::updateLifecyclePhasesInternal(
     DocumentLifecycle::LifecycleState targetState) {
   if (m_currentUpdateLifecyclePhasesTargetState !=
       DocumentLifecycle::Uninitialized) {
     NOTREACHED() << "FrameView::updateLifecyclePhasesInternal() reentrance";
     return;
   }
 
@@ skipping 12 matching lines @@
 
   AutoReset<DocumentLifecycle::LifecycleState> targetStateScope(
       &m_currentUpdateLifecyclePhasesTargetState, targetState);
 
   if (shouldThrottleRendering()) {
     updateViewportIntersectionsForSubtree(
         std::min(targetState, DocumentLifecycle::CompositingClean));
     return;
   }
 
+  if (RuntimeEnabledFeatures::printBrowserEnabled()) {
+    setupPrintContext();
+  } else {
+    clearPrintContext();
+  }

[mstensho (USE GERRIT), 2017/02/08 14:32:29]

No need for the curly braces.

[gozzard, 2017/02/09 04:17:25]

Done.

+
   updateStyleAndLayoutIfNeededRecursive();
   DCHECK(lifecycle().state() >= DocumentLifecycle::LayoutClean);
 
   if (targetState == DocumentLifecycle::LayoutClean) {
     updateViewportIntersectionsForSubtree(targetState);
     return;
   }
 
   forAllNonThrottledFrameViews([](FrameView& frameView) {
     frameView.performScrollAnchoringAdjustments();
@@ skipping 52 matching lines @@
       // TODO(pdr): prePaint should be under the "Paint" devtools timeline step
       // for slimming paint v2.
       if (targetState >= DocumentLifecycle::PrePaintClean)
         prePaint();
     }
 
     if (RuntimeEnabledFeatures::slimmingPaintV2Enabled())
       DocumentAnimations::updateAnimations(layoutView()->document());
 
     if (targetState == DocumentLifecycle::PaintClean) {
-      if (!m_frame->document()->printing())
+      if (!m_frame->document()->printing() ||
+          RuntimeEnabledFeatures::printBrowserEnabled())
         paintTree();
 
       if (RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         pushPaintArtifactToCompositor();
 
       DCHECK(!view.hasPendingSelection());
       DCHECK((m_frame->document()->printing() &&
               lifecycle().state() == DocumentLifecycle::PrePaintClean) ||
              lifecycle().state() == DocumentLifecycle::PaintClean);
     }
@@ skipping 71 matching lines @@
 
   LayoutViewItem view = layoutViewItem();
   ASSERT(!view.isNull());
   forAllNonThrottledFrameViews([](FrameView& frameView) {
     frameView.lifecycle().advanceTo(DocumentLifecycle::InPaint);
   });
 
   if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
     if (layoutView()->layer()->needsRepaint()) {
       GraphicsContext graphicsContext(*m_paintController);
+      if (RuntimeEnabledFeatures::printBrowserEnabled())
+        graphicsContext.setPrinting(true);
       paint(graphicsContext, CullRect(LayoutRect::infiniteIntRect()));
       m_paintController->commitNewDisplayItems(LayoutSize());
       notifyPaint(*m_paintController);
     }
   } else {
     // A null graphics layer can occur for painting of SVG images that are not
     // parented into the main frame tree, or when the FrameView is the main
     // frame view of a page overlay. The page overlay is in the layer tree of
     // the host page and will be painted during painting of the host page.
     if (GraphicsLayer* rootGraphicsLayer =
@@ skipping 2000 matching lines @@
     std::unique_ptr<CompositorAnimationTimeline> timeline) {
   m_animationTimeline = std::move(timeline);
 }
 
 void FrameView::setAnimationHost(
     std::unique_ptr<CompositorAnimationHost> host) {
   m_animationHost = std::move(host);
 }
 
 }  // namespace blink