Display fixed position objects on every page of paged media.

third_party/WebKit/Source/core/paint/BlockPainter.cpp

Index: third_party/WebKit/Source/core/paint/BlockPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/BlockPainter.cpp b/third_party/WebKit/Source/core/paint/BlockPainter.cpp
index be32974edac3edfc798fc3d83168dcca42f59ae0..3a8f8ca70e35fb1043e6768bdffa835157965257 100644
--- a/third_party/WebKit/Source/core/paint/BlockPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/BlockPainter.cpp
@@ -10,6 +10,7 @@
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/layout/LayoutFlexibleBox.h"
 #include "core/layout/LayoutInline.h"
+#include "core/layout/LayoutView.h"
 #include "core/layout/api/LineLayoutBox.h"
 #include "core/page/Page.h"
 #include "core/paint/BoxClipper.h"
@@ -69,6 +70,31 @@ void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOff
     paintOverflowControlsIfNeeded(localPaintInfo, adjustedPaintOffset);
 }
 
+void BlockPainter::paintFixedPositionObjectsOnAllPages(const PaintInfo& localPaintInfo, const LayoutPoint& paintOffset)
+{
+    // For paged media, boxes with fixed positions are repeated on every page.

[mstensho (USE GERRIT), 2016/01/11 19:54:51]

I think this approach is wrong. This would be in the wrong paint order, and I
suspect that they would even be painted doubly on the first page, since they
already got painted on the first page prior to your changes, and with this code
they'll be painted again.

And aren't you going to miss fixedpos objects that live inside other fixedpos
objects. Those aren't in the positioned descendants list of the root element,
are they?

[rhogan, 2016/01/14 12:10:44]

OK I don't have enough of a clue about painting to know what the right thing to
do is here. I can't seem to paint the same object multiple times if I try to do
it from within the object's BlockPainter::paint() so I think I need to paint
from the HTML object like I'm currently doing but in some way that better
preserves paint order.
No, I do actually skip the first page so there's no double painting.
They are aren't they?

[Xianzhu, 2016/02/24 19:22:51]

I also think the current patch is incorrect about painting order. You don't need
to paint the same object multiple times by yourself. This is handled by
PaintLayerPainter or WebLocalFrameImpl. I think you just need to adjust the
paint offset of the fixedpos object when it's painted.
I confirm that the following code can find all viewport contained fixedpos
objects.

[rhogan, 2016/02/25 20:33:04]

When I do that it doesn't paint at all. 

--- a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
@@ -1274,6 +1274,19 @@ void LayoutBlock::paintChildren(const PaintInfo&
paintInfo, const LayoutPoint& p
 void LayoutBlock::paintObject(const PaintInfo& paintInfo, const LayoutPoint&
paintOffset) const
 {
     BlockPainter(*this).paintObject(paintInfo, paintOffset);
+    if (!view()->document().printing() || style()->position() != FixedPosition)
+        return;
+    LayoutView* view = this->view();
+    HTMLElement* body = document().body();
+    LayoutObject* bodyObject = isHTMLBodyElement(body) ? body->layoutObject() :
0;
+    if (!bodyObject)
+        return;
+    int pages = toLayoutBlock(bodyObject)->logicalHeight() /
view->pageLogicalHeight();
+    LayoutPoint adjustedPaintOffset = paintOffset;
+    for (int i = 0; i < pages; i++) {
+        adjustedPaintOffset += LayoutPoint(0, view->pageLogicalHeight());
+        BlockPainter(*this).paintObject(paintInfo, adjustedPaintOffset);
+    }
 }
 

Am I missing your point? Where should I be adjusting the offset?

+    if (!m_layoutBlock.parent() || !m_layoutBlock.parent()->isLayoutView())
+        return;
+
+    LayoutView* view = toLayoutView(m_layoutBlock.parent());
+    if (!view->pageLogicalHeight())
+        return;
+
+    TrackedLayoutBoxListHashSet* positionedDescendants = view->positionedObjects();
+    if (!positionedDescendants)
+        return;
+    int pages = m_layoutBlock.logicalHeight() / view->pageLogicalHeight();
+    for (auto* positionedObject : *positionedDescendants) {
+        if (positionedObject->style()->position() != FixedPosition)
+            continue;
+        LayoutPoint adjustedPaintOffset = paintOffset + toLayoutBlock(positionedObject)->location();
+        for (int i = 0; i < pages; i++) {
+            adjustedPaintOffset += LayoutPoint(0, view->pageLogicalHeight());
+            toLayoutBlock(positionedObject)->paintObject(localPaintInfo, adjustedPaintOffset);
+        }
+    }
+}
+
 void BlockPainter::paintOverflowControlsIfNeeded(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     PaintPhase phase = paintInfo.phase;
@@ -270,6 +296,7 @@ void BlockPainter::paintContents(const PaintInfo& paintInfo, const LayoutPoint&
         paintInfoForChild.updatePaintingRootForChildren(&m_layoutBlock);
         m_layoutBlock.paintChildren(paintInfoForChild, paintOffset);
     }
+    paintFixedPositionObjectsOnAllPages(paintInfo, paintOffset);
 }
 
 } // namespace blink