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

@@ -134,6 +134,8 @@ private:
     // the buffering style
     int m_style;
 
+    wxSize m_area;
+    
     DECLARE_DYNAMIC_CLASS(wxBufferedDC)
     wxDECLARE_NO_COPY_CLASS(wxBufferedDC);
 };

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
+    // It's possible that the buffer may be bigger than the area that needs to
-    // reused for a smaller one later) we should only blit the real bitmap area
+    // be drawn (the client size of the window is smaller than the bitmap, or
-    // and not the full allocated back buffer
+    // a shared bitmap has been reused for a smaller area, etc.) so avoid
-    int widthDC,
+    // blitting too much if possible, but only use the real DC size if the
-        heightDC;
+    // wxBUFFER_VIRTUAL_AREA style is not set.
+    int width = m_area.GetWidth(),
+        height = m_area.GetHeight();
 
-    m_dc->GetSize(&widthDC, &heightDC);
+    if (! m_style & wxBUFFER_VIRTUAL_AREA)
+    {
+        int widthDC,
+            heightDC;
+        m_dc->GetSize(&widthDC, &heightDC);
+        width = wxMin(width, widthDC);
+        height = wxMin(height, heightDC);
+    }
 
-    int widthBuf = m_buffer->GetWidth(),
+    m_dc->Blit(0, 0, width, height, this, -x, -y);
-        heightBuf = m_buffer->GetHeight();
-
-    m_dc->Blit(0, 0,
-               wxMin(widthDC, widthBuf), wxMin(heightDC, heightBuf),
-               this,
-               -x, -y);
     m_dc = NULL;
 
     if ( m_style & wxBUFFER_USES_SHARED_BUFFER )