Bug 1640197 - Part 4: Create more pages for vertical overflow r=dholbert,mats

Depends on D90425

Differential Revision: https://phabricator.services.mozilla.com/D90426

layout/generic/nsAbsoluteContainingBlock.cpp

@@ -156,8 +156,15 @@ void nsAbsoluteContainingBlock::Reflow(nsContainerFrame* aDelegatingFrame,
                                        const nsRect& aContainingBlock,
                                        AbsPosReflowFlags aFlags,
                                        nsOverflowAreas* aOverflowAreas) {
-  nsReflowStatus reflowStatus;
+  // PageContentFrame replicates fixed pos children so we really don't want
+  // them contributing to overflow areas because that means we'll create new
+  // pages ad infinitum if one of them overflows the page.
+  if (aDelegatingFrame->IsPageContentFrame()) {
+    MOZ_ASSERT(mChildListID == nsAtomicContainerFrame::kFixedList);
+    aOverflowAreas = nullptr;
+  }
 
+  nsReflowStatus reflowStatus;
   const bool reflowAll = aReflowInput.ShouldReflowAllKids();
   const bool isGrid = !!(aFlags & AbsPosReflowFlags::IsGridContainerCB);
   nsIFrame* kidFrame;

layout/generic/nsPageContentFrame.cpp

@@ -6,6 +6,7 @@
 #include "nsPageContentFrame.h"
 
 #include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_layout.h"
 
 #include "nsCSSFrameConstructor.h"
 #include "nsPresContext.h"
@@ -114,6 +115,29 @@ void nsPageContentFrame::Reflow(nsPresContext* aPresContext,
   }
   FinishAndStoreOverflow(&aReflowOutput);
 
+  if (StaticPrefs::layout_display_list_improve_fragmentation() &&
+      mFrames.NotEmpty()) {
+    auto* previous = static_cast<nsPageContentFrame*>(GetPrevContinuation());
+    const nscoord previousPageOverflow =
+        previous ? previous->mRemainingOverflow : 0;
+
+    const nscoord overflowHeight = InkOverflowRect().YMost();
+    const nscoord pageHeight = GetRect().Height();
+    const nscoord currentPageOverflow = overflowHeight - pageHeight;
+
+    nscoord remainingOverflow =
+        std::max(currentPageOverflow, previousPageOverflow - pageHeight);
+    if (aStatus.IsFullyComplete() && remainingOverflow > 0) {
+      // If we have InkOverflow off the end of our page, then we report
+      // ourselves as overflow-incomplete in order to produce an additional
+      // content-less page, which we expect to draw our InkOverflow on our
+      // behalf.
+      aStatus.SetOverflowIncomplete();
+    }
+
+    mRemainingOverflow = std::max(remainingOverflow, 0);
+  }
+
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowInput, aReflowOutput);
 }
 

layout/generic/nsPageContentFrame.h

@@ -57,6 +57,10 @@ class nsPageContentFrame final : public mozilla::ViewportFrame {
   // Note: this will be set before reflow, and it's strongly owned by our
   // nsPageSequenceFrame, which outlives us.
   nsSharedPageData* mPD = nullptr;
+
+  // The combined InkOverflow from the previous and current page that does not
+  // yet have space allocated for it.
+  nscoord mRemainingOverflow = 0;
 };
 
 #endif /* nsPageContentFrame_h___ */