special casing mac code

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

diff --git a/src/common/dcbufcmn.cpp b/src/common/dcbufcmn.cpp
index 4d4083603e0ab604ea3e4776ad56e0574e40f19b..6ae9f3ef8240df581a5d6707601d971c8c487201 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);
         }
 
@@ -120,8 +128,21 @@ 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 )