try to merge rectangles already in AddPaintRect()

It turns out that e.g. adding a new line in Writer results
in a number of paint rectangles that actually often line up and
form a large rectangle. So try to detect these and merge them
directly, resulting in less work for SwRegionsRects::Compress().

Change-Id: If89ae9463d9c80a1492431afd37bcedfd24bea2d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/123077
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/sw/source/core/view/viewimp.cxx b/sw/source/core/view/viewimp.cxx
index e2243bb1ad88..abb2ef6b174a 100644
--- a/sw/source/core/view/viewimp.cxx
+++ b/sw/source/core/view/viewimp.cxx
@@ -126,6 +126,32 @@ bool SwViewShellImp::AddPaintRect( const SwRect &rRect )
             m_pPaintRegion.reset(new SwRegionRects);
             m_pPaintRegion->ChangeOrigin(rArea);
         }
+        if(!m_pPaintRegion->empty())
+        {
+            // This function often gets called with rectangles that line up vertically.
+            // Try to extend the last one downwards to include the new one.
+            SwRect& last = m_pPaintRegion->back();
+            if(last.Left() == rRect.Left() && last.Width() == rRect.Width()
+                && last.Bottom() + 1 >= rRect.Top() && last.Bottom() <= rRect.Bottom())
+            {
+                last = SwRect( last.TopLeft(), rRect.BottomRight());
+                // And these rectangles lined up vertically often come up in groups
+                // that line up horizontally. Try to extend the previous rectangle
+                // to the right to include the last one.
+                if(m_pPaintRegion->size() > 1)
+                {
+                    SwRect& last2 = (*m_pPaintRegion)[m_pPaintRegion->size() - 2];
+                    if(last2.Top() == last.Top() && last2.Height() == last.Height()
+                        && last2.Right() + 1 >= last.Left() && last2.Right() <= last2.Right())
+                    {
+                        last2 = SwRect( last.TopLeft(), rRect.BottomRight());
+                        m_pPaintRegion->pop_back();
+                        return true;
+                    }
+                }
+                return true;
+            }
+        }
         (*m_pPaintRegion) += rRect;
         return true;
     }