Simplify and correct bugs in wxMSW wxScrollBar message handling.

[wxWidgets.git] / src / common / dcbufcmn.cpp

diff --git a/src/common/dcbufcmn.cpp b/src/common/dcbufcmn.cpp
index 4d4083603e0ab604ea3e4776ad56e0574e40f19b..1d339f8ba0592833c42c46df54a83b732bd47645 100644 (file)
--- a/src/common/dcbufcmn.cpp
+++ b/src/common/dcbufcmn.cpp
@@ -59,6 +59,14 @@ public:
                     h > ms_buffer->GetHeight() )
         {
             delete ms_buffer;
+
+            // we must always return a valid bitmap but creating a bitmap of
+            // size 0 would fail, so create a 1*1 bitmap in this case
+            if ( !w )
+                w = 1;
+            if ( !h )
+                h = 1;
+
             ms_buffer = new wxBitmap(w, h);
         }
 
@@ -107,12 +115,17 @@ void wxBufferedDC::UseBuffer(wxCoord w, wxCoord h)
     }
 
     SelectObject(*m_buffer);
+
+    // now that the DC is valid we can inherit the attributes (fonts, colours,
+    // layout direction, ...) from the original DC
+    if ( m_dc->IsOk() )
+        CopyAttributes(*m_dc);
 }
 
 void wxBufferedDC::UnMask()
 {
-    wxCHECK_RET( m_dc, _T("no underlying wxDC?") );
-    wxASSERT_MSG( m_buffer && m_buffer->IsOk(), _T("invalid backing store") );
+    wxCHECK_RET( m_dc, wxT("no underlying wxDC?") );
+    wxASSERT_MSG( m_buffer && m_buffer->IsOk(), wxT("invalid backing store") );
 
     wxCoord x = 0,
             y = 0;
@@ -120,8 +133,21 @@ void wxBufferedDC::UnMask()
     if ( m_style & wxBUFFER_CLIENT_AREA )
         GetDeviceOrigin(&x, &y);
 
-    m_dc->Blit(0, 0, m_buffer->GetWidth(), m_buffer->GetHeight(),
-               this, -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;
+
+    m_dc->GetSize(&widthDC, &heightDC);
+
+    int widthBuf = m_buffer->GetWidth(),
+        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 )