From 3754c85628ecbf760df3aff2615cbf7c4e8bcf03 Mon Sep 17 00:00:00 2001
From: Robin Dunn <robin@alldunn.com>
Date: Wed, 1 Nov 2006 02:07:36 +0000
Subject: [PATCH] Switch wxBufferedDC to use a wxBitmap* internally, so it
 doesn't increment the refcount of the bitmap refdata, and so it doesn't do a
 copy on write.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42884 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---
 include/wx/dcbuffer.h   | 19 ++++++++++---------
 src/common/dcbufcmn.cpp | 11 ++++++-----
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/include/wx/dcbuffer.h b/include/wx/dcbuffer.h
index bce4780cc0..ef5383bbdf 100644
--- a/include/wx/dcbuffer.h
+++ b/include/wx/dcbuffer.h
@@ -43,15 +43,16 @@ public:
     // Default ctor, must subsequently call Init for two stage construction.
     wxBufferedDC()
         : m_dc(NULL),
+          m_buffer(NULL),
           m_style(0)
     {
     }
 
     // Construct a wxBufferedDC using a user supplied buffer.
     wxBufferedDC(wxDC *dc,
-                 const wxBitmap& buffer = wxNullBitmap,
+                 wxBitmap& buffer = wxNullBitmap,
                  int style = wxBUFFER_CLIENT_AREA)
-        : m_dc(NULL)
+        : m_dc(NULL), m_buffer(NULL)
     {
         Init(dc, buffer, style);
     }
@@ -60,7 +61,7 @@ public:
     // (where area is usually something like the size of the window
     // being buffered)
     wxBufferedDC(wxDC *dc, const wxSize& area, int style = wxBUFFER_CLIENT_AREA)
-        : m_dc(NULL)
+        : m_dc(NULL), m_buffer(NULL)
     {
         Init(dc, area, style);
     }
@@ -74,12 +75,12 @@ public:
 
     // These reimplement the actions of the ctors for two stage creation
     void Init(wxDC *dc,
-              const wxBitmap& buffer = wxNullBitmap,
+              wxBitmap& buffer = wxNullBitmap,
               int style = wxBUFFER_CLIENT_AREA)
     {
         InitCommon(dc, style);
 
-        m_buffer = buffer;
+        m_buffer = &buffer;
 
         UseBuffer();
     }
@@ -100,7 +101,7 @@ public:
     void UnMask()
     {
         wxCHECK_RET( m_dc, _T("no underlying wxDC?") );
-        wxASSERT_MSG( m_buffer.IsOk(), _T("invalid backing store") );
+        wxASSERT_MSG( m_buffer && m_buffer->IsOk(), _T("invalid backing store") );
 
         wxCoord x = 0,
                 y = 0;
@@ -108,7 +109,7 @@ public:
         if ( m_style & wxBUFFER_CLIENT_AREA )
             GetDeviceOrigin(&x, &y);
 
-        m_dc->Blit(0, 0, m_buffer.GetWidth(), m_buffer.GetHeight(),
+        m_dc->Blit(0, 0, m_buffer->GetWidth(), m_buffer->GetHeight(),
                    this, -x, -y );
         m_dc = NULL;
     }
@@ -142,7 +143,7 @@ private:
     wxDC *m_dc;
 
     // the buffer (selected in this DC), initially invalid
-    wxBitmap m_buffer;
+    wxBitmap *m_buffer;
 
     // the buffering style
     int m_style;
@@ -162,7 +163,7 @@ class WXDLLEXPORT wxBufferedPaintDC : public wxBufferedDC
 {
 public:
     // If no bitmap is supplied by the user, a temporary one will be created.
-    wxBufferedPaintDC(wxWindow *window, const wxBitmap& buffer, int style = wxBUFFER_CLIENT_AREA)
+    wxBufferedPaintDC(wxWindow *window, wxBitmap& buffer, int style = wxBUFFER_CLIENT_AREA)
         : m_paintdc(window)
     {
         // If we're buffering the virtual window, scale the paint DC as well
diff --git a/src/common/dcbufcmn.cpp b/src/common/dcbufcmn.cpp
index 686daadc77..70a7c8b976 100644
--- a/src/common/dcbufcmn.cpp
+++ b/src/common/dcbufcmn.cpp
@@ -46,7 +46,7 @@ public:
     virtual bool OnInit() { return true; }
     virtual void OnExit() { wxDELETE(ms_buffer); }
 
-    static wxBitmap GetBuffer(int w, int h)
+    static wxBitmap* GetBuffer(int w, int h)
     {
         if ( !ms_buffer ||
                 w > ms_buffer->GetWidth() ||
@@ -56,7 +56,8 @@ public:
             ms_buffer = new wxBitmap(w, h);
         }
 
-        return *ms_buffer;
+        // return a copy of the static instance
+        return ms_buffer;
     }
 
 private:
@@ -65,7 +66,7 @@ private:
     DECLARE_DYNAMIC_CLASS(wxSharedDCBufferManager)
 };
 
-wxBitmap* wxSharedDCBufferManager::ms_buffer;
+wxBitmap* wxSharedDCBufferManager::ms_buffer = NULL;
 
 IMPLEMENT_DYNAMIC_CLASS(wxSharedDCBufferManager, wxModule)
 
@@ -75,7 +76,7 @@ IMPLEMENT_DYNAMIC_CLASS(wxSharedDCBufferManager, wxModule)
 
 void wxBufferedDC::UseBuffer(wxCoord w, wxCoord h)
 {
-    if ( !m_buffer.IsOk() )
+    if ( !m_buffer || !m_buffer->IsOk() )
     {
         if ( w == -1 || h == -1 )
             m_dc->GetSize(&w, &h);
@@ -83,6 +84,6 @@ void wxBufferedDC::UseBuffer(wxCoord w, wxCoord h)
         m_buffer = wxSharedDCBufferManager::GetBuffer(w, h);
     }
 
-    SelectObject(m_buffer);
+    SelectObject(*m_buffer);
 }
 
-- 
2.47.2