From 0681e07a14b413b426366005f1c24f88b8702733 Mon Sep 17 00:00:00 2001
From: Robin Dunn <robin@alldunn.com>
Date: Fri, 8 Jun 2012 19:26:19 +0000
Subject: [PATCH] Keep track of the area intended to be buffered, and use that
 in UnMask instead of defaulting to the buffer size.  Only clip to the DC size
 if wxBUFFER_VIRTUAL_AREA is not set.  This fixes the issue where buffering
 the full virtual area in a wxScrolledWindow would only draw an area the
 physical size of the window.  Fixes #11612.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71704 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---
 include/wx/dcbuffer.h   |  2 ++
 src/common/dcbufcmn.cpp | 32 +++++++++++++++++++-------------
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/include/wx/dcbuffer.h b/include/wx/dcbuffer.h
index 521113e0c8..40cb8179cd 100644
--- a/include/wx/dcbuffer.h
+++ b/include/wx/dcbuffer.h
@@ -134,6 +134,8 @@ private:
     // the buffering style
     int m_style;
 
+    wxSize m_area;
+    
     DECLARE_DYNAMIC_CLASS(wxBufferedDC)
     wxDECLARE_NO_COPY_CLASS(wxBufferedDC);
 };
diff --git a/src/common/dcbufcmn.cpp b/src/common/dcbufcmn.cpp
index 2a8314d43e..d625c72f8f 100644
--- a/src/common/dcbufcmn.cpp
+++ b/src/common/dcbufcmn.cpp
@@ -114,7 +114,10 @@ void wxBufferedDC::UseBuffer(wxCoord w, wxCoord h)
 
         m_buffer = wxSharedDCBufferManager::GetBuffer(w, h);
         m_style |= wxBUFFER_USES_SHARED_BUFFER;
+        m_area.Set(w,h);
     }
+    else
+        m_area = m_buffer->GetSize();
 
     SelectObject(*m_buffer);
 
@@ -138,21 +141,24 @@ void wxBufferedDC::UnMask()
     if ( m_style & wxBUFFER_CLIENT_AREA )
         GetDeviceOrigin(&x, &y);
 
-    // avoid blitting too much: if we were created for a bigger bitmap (and
-    // reused for a smaller one later) we should only blit the real bitmap area
-    // and not the full allocated back buffer
-    int widthDC,
-        heightDC;
+    // It's possible that the buffer may be bigger than the area that needs to
+    // be drawn (the client size of the window is smaller than the bitmap, or
+    // a shared bitmap has been reused for a smaller area, etc.) so avoid
+    // blitting too much if possible, but only use the real DC size if the
+    // wxBUFFER_VIRTUAL_AREA style is not set.
+    int width = m_area.GetWidth(),
+        height = m_area.GetHeight();
 
-    m_dc->GetSize(&widthDC, &heightDC);
-
-    int widthBuf = m_buffer->GetWidth(),
-        heightBuf = m_buffer->GetHeight();
+    if (! m_style & wxBUFFER_VIRTUAL_AREA)
+    {
+        int widthDC,
+            heightDC;
+        m_dc->GetSize(&widthDC, &heightDC);
+        width = wxMin(width, widthDC);
+        height = wxMin(height, heightDC);
+    }
 
-    m_dc->Blit(0, 0,
-               wxMin(widthDC, widthBuf), wxMin(heightDC, heightBuf),
-               this,
-               -x, -y);
+    m_dc->Blit(0, 0, width, height, this, -x, -y);
     m_dc = NULL;
 
     if ( m_style & wxBUFFER_USES_SHARED_BUFFER )
-- 
2.45.2