opengl: improve overlap tracking

Insteado of tracking the overlap with only one rectangle use more
rectangles and add elements to the rectangle that increases the
combined area the least. If a new entry overlaps with at least
on rectangle then create a new list. Current limit the number of
rectangles to 30.

Change-Id: I3db619afc1fdd98fe7314c930e909bf2c93d7b2c

1 files changed, 46 insertions, 5 deletions

diff --git a/vcl/inc/opengl/RenderList.hxx b/vcl/inc/opengl/RenderList.hxx
index 32ece7360b21..e63f5dcb4566 100644
--- a/vcl/inc/opengl/RenderList.hxx
+++ b/vcl/inc/opengl/RenderList.hxx
@@ -38,6 +38,8 @@ struct RenderTextureParameters
 
 struct RenderEntry
 {
+    basegfx::B2DRange maOverlapTrackingRectangle;
+
     RenderParameters maTriangleParameters;
     RenderParameters maLineParameters;
     RenderParameters maLineAAParameters;
@@ -68,19 +70,59 @@ struct RenderEntry
 class RenderList
 {
 private:
-    basegfx::B2DRange maOverlapTrackingRectangle;
     std::vector<RenderEntry> maRenderEntries;
+    std::vector<basegfx::B2DRange> maRectangles;
+
+    bool doesOverlap(const basegfx::B2DRange& rDrawRectangle)
+    {
+        if (!maRenderEntries.back().maOverlapTrackingRectangle.overlaps(rDrawRectangle))
+            return false;
+
+        for (const basegfx::B2DRange& rRectangle : maRectangles)
+        {
+            if (rRectangle.overlaps(rDrawRectangle))
+                return true;
+        }
+        return false;
+    }
 
     void checkOverlapping(const basegfx::B2DRange& rDrawRectangle)
     {
-        if (maRenderEntries.empty() || maOverlapTrackingRectangle.overlaps(rDrawRectangle))
+        if (maRenderEntries.empty() || doesOverlap(rDrawRectangle))
         {
             maRenderEntries.resize(maRenderEntries.size() + 1);
-            maOverlapTrackingRectangle = rDrawRectangle;
+            maRenderEntries.back().maOverlapTrackingRectangle = rDrawRectangle;
+
+            maRectangles.clear();
+            maRectangles.reserve(30);
+            maRectangles.push_back(rDrawRectangle);
         }
         else
         {
-            maOverlapTrackingRectangle.expand(rDrawRectangle);
+            maRenderEntries.back().maOverlapTrackingRectangle.expand(rDrawRectangle);
+
+            if (maRectangles.size() < 30)
+            {
+                maRectangles.push_back(rDrawRectangle);
+            }
+            else
+            {
+                basegfx::B2DRange aTempRectangle(maRectangles[0]);
+                aTempRectangle.expand(rDrawRectangle);
+                double minArea = aTempRectangle.getWidth() * aTempRectangle.getHeight();
+                size_t index = 0;
+
+                double area;
+                for (size_t i = 1; i < maRectangles.size(); ++i)
+                {
+                    aTempRectangle = basegfx::B2DRange(maRectangles[i]);
+                    aTempRectangle.expand(rDrawRectangle);
+                    area = aTempRectangle.getWidth() * aTempRectangle.getHeight();
+                    if (area < minArea)
+                        index = i;
+                }
+                maRectangles[index].expand(rDrawRectangle);
+            }
         }
     }
 
@@ -96,7 +138,6 @@ public:
     void clear()
     {
         maRenderEntries.clear();
-        maOverlapTrackingRectangle.reset();
     }
 
     std::vector<RenderEntry>& getEntries()