From c58d81d32d7faa6dd53a124f27675b3d50b5567b Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Thu, 24 May 2018 17:46:14 +0200
Subject: [PATCH] Simplify wxHtmlPageBreakCell::AdjustPagebreak()

There is no need to look in the known page breaks array for a page break
at the position of this cell, all we care about is whether this cell is
on the current page or not: we must insert a page break if, and only if,
it is.

No real changes in behaviour, but the code is now much simpler to
understand and this change paves way for removing "known_pagebreaks"
entirely, as it was only added for the use in this function (see
f2034f1b6e04a39f6d882cf6cdd53c11bf39f5d7 from 15 years ago), which
doesn't even actually need it.

It should also make pagination code somewhat faster.
---
 src/html/m_layout.cpp | 44 ++++++++-----------------------------------
 1 file changed, 8 insertions(+), 36 deletions(-)

diff --git a/src/html/m_layout.cpp b/src/html/m_layout.cpp
index 619ec2bb08..4dba82e6d1 100644
--- a/src/html/m_layout.cpp
+++ b/src/html/m_layout.cpp
@@ -80,47 +80,19 @@ private:
 
 bool
 wxHtmlPageBreakCell::AdjustPagebreak(int* pagebreak,
-                                     const wxArrayInt& known_pagebreaks,
-                                     int WXUNUSED(pageHeight)) const
+                                     const wxArrayInt& WXUNUSED(known_pagebreaks),
+                                     int pageHeight) const
 {
-    // When we are counting pages, 'known_pagebreaks' is non-NULL.
-    // That's the only time we change 'pagebreak'. Otherwise, pages
-    // were already counted, 'known_pagebreaks' is NULL, and we don't
-    // do anything except return false.
-    //
-    // We also simply return false if the 'pagebreak' argument is
-    // less than (vertically above) or the same as the current
-    // vertical position. Otherwise we'd be setting a pagebreak above
-    // the current cell, which is incorrect, or duplicating a
-    // pagebreak that has already been set.
-    if( known_pagebreaks.GetCount() == 0 || *pagebreak <= m_PosY)
-    {
-        return false;
-    }
-
-    // m_PosY is only the vertical offset from the parent. The pagebreak
-    // required here is the total page offset, so m_PosY must be added
-    // to the parent's offset and height.
-    int total_height = m_PosY;
-    for ( wxHtmlCell *parent = GetParent(); parent; parent = parent->GetParent() )
-    {
-        total_height += parent->GetPosY();
-    }
-
-
-    // Search the array of pagebreaks to see whether we've already set
-    // a pagebreak here.
-    int where = known_pagebreaks.Index( total_height);
-    // Add a pagebreak only if there isn't one already set here.
-    if( wxNOT_FOUND != where)
-    {
-        return false;
-    }
-    else
+    // Request a page break at the position of this cell if it's on the current
+    // page. Note that it's important not to do it unconditionally or we could
+    // end up in an infinite number of page breaks at this cell position.
+    if ( m_PosY < *pagebreak && m_PosY > *pagebreak - pageHeight )
     {
         *pagebreak = m_PosY;
         return true;
     }
+
+    return false;
 }