Display fixed position objects on every page of paged media.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 0a6252bb97619ba13f0f2ee27db062730789b882..577e3faed94dfbf51e8e375afe24aa6efc97120b 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -454,9 +454,23 @@ PaintLayerPainter::PaintResult PaintLayerPainter::paintLayerWithTransform(Graphi
         ancestorBackgroundClipRect = m_paintLayer.clipper().backgroundClipRect(clipRectsContext);
     }
 
+    LayoutObject* object = m_paintLayer.layoutObject();
+    LayoutView* view = object->view();
+    bool isFixedPosObjectInPagedMedia = object->style()->position() == FixedPosition && view->pageLogicalHeight();

[Xianzhu, 2016/03/21 19:37:18]

We should exclude the case that the view is not the container of the fixed-pos
element (e.g. if the fixed-pos element is under a transformed element).

We may need to add another condition here: ... && view ==
object->containerForFixedPosition().

     PaintLayer* paginationLayer = m_paintLayer.enclosingPaginationLayer();
     PaintLayerFragments fragments;
-    if (paginationLayer) {
+    if (isFixedPosObjectInPagedMedia) {
+        // "For paged media, boxes with fixed positions are repeated on every page."

[Xianzhu, 2016/03/21 19:37:18]

Nit: include the link of source of the above statement.

+        ASSERT(view->firstChild() && view->firstChild()->isLayoutBlock());
+        int pages = toLayoutBlock(view->firstChild())->logicalHeight() / view->pageLogicalHeight();
+        LayoutPoint paginationOffset;
+        for (int i = 0; i <= pages; i++) {
+            PaintLayerFragment fragment;
+            fragment.paginationOffset = paginationOffset;
+            fragments.append(fragment);
+            paginationOffset += LayoutPoint(0, view->pageLogicalHeight());
+        }
+    } else if (paginationLayer) {
         // FIXME: This is a mess. Look closely at this code and the code in Layer and fix any
         // issues in it & refactor to make it obvious from code structure what it does and that it's
         // correct.
@@ -484,7 +498,7 @@ PaintLayerPainter::PaintResult PaintLayerPainter::paintLayerWithTransform(Graphi
         if (needsScope)
             scopeRecorder.emplace(context);
         Optional<LayerClipRecorder> clipRecorder;
-        if (parentLayer) {
+        if (parentLayer && !isFixedPosObjectInPagedMedia) {

[Xianzhu, 2016/03/21 19:37:18]

I think we should still clip (especially css clip) fixed-pos elements.

For example:
<div style="clip: rect(0, 100px, 5000px, 0)>
  <div style="position: fixed; ..."></div>
</div>

I think in this case, whether the fixed-pos element appears in all pages depends
on how big the clip is.

             ClipRect clipRectForFragment(ancestorBackgroundClipRect);
             clipRectForFragment.moveBy(fragment.paginationOffset);
             clipRectForFragment.intersect(fragment.backgroundRect);