Implement wxTreeCtrl::SetDoubleBuffered() in MSW wxTreeCtrl

Also don't erase background when the control is double-buffered because
it's not necessary and can cause flicker.

See https://github.com/wxWidgets/wxWidgets/pull/374

docs/changes.txt

@@ -443,6 +443,7 @@ wxMSW:
 - Use correct parent for the native modal dialogs (Andreas Falkenhahn).
 - Fix layout of wxSlider with wxSL_VALUE_LABEL only (gafatoa).
 - Fix flicker when resizing columns of report-mode wxListCtrl.
+- Implement wxTreeCtrl::SetDoubleBuffered() (Steve Browne).
 
 wxOSX/Cocoa:
 

include/wx/msw/missing.h

@@ -239,6 +239,10 @@
     #define TV_FIRST                0x1100
 #endif
 
+#ifndef TVS_EX_DOUBLEBUFFER
+    #define TVS_EX_DOUBLEBUFFER     0x0004
+#endif
+
 #ifndef TVS_FULLROWSELECT
     #define TVS_FULLROWSELECT       0x1000
 #endif
@@ -248,6 +252,11 @@
     #define TVM_SETTEXTCOLOR        (TV_FIRST + 30)
 #endif
 
+#ifndef TVM_SETEXTENDEDSTYLE
+    #define TVM_SETEXTENDEDSTYLE    (TV_FIRST + 44)
+    #define TVM_GETEXTENDEDSTYLE    (TV_FIRST + 45)
+#endif
+
 // Various defines used by the webview library that are needed by mingw 
 
 #ifndef DISPID_COMMANDSTATECHANGE

include/wx/msw/treectrl.h

@@ -202,6 +202,9 @@ public:
     // returns true if the platform should explicitly apply a theme border
     virtual bool CanApplyThemeBorder() const wxOVERRIDE { return false; }
 
+    virtual bool IsDoubleBuffered() const wxOVERRIDE;
+    virtual void SetDoubleBuffered(bool on) wxOVERRIDE;
+
 protected:
     // Implement "update locking" in a custom way for this control.
     virtual void DoFreeze() wxOVERRIDE;

src/msw/treectrl.cpp

@@ -795,6 +795,46 @@ bool wxTreeCtrl::Create(wxWindow *parent,
     return true;
 }
 
+bool wxTreeCtrl::IsDoubleBuffered() const
+{
+    if ( !GetHwnd() )
+        return false;
+
+    // Notice that TVM_GETEXTENDEDSTYLE is supported since XP, so we can always
+    // send this message, no need for comctl32.dll version check here.
+    const LRESULT
+        exTreeStyle = ::SendMessage(GetHwnd(), TVM_GETEXTENDEDSTYLE, 0, 0);
+
+    return (exTreeStyle & TVS_EX_DOUBLEBUFFER) != 0;
+}
+
+void wxTreeCtrl::SetDoubleBuffered(bool on)
+{
+    if ( !GetHwnd() )
+        return;
+
+    // TVS_EX_DOUBLEBUFFER is only supported since Vista, don't try to set it
+    // under XP, who knows what could this do.
+    if ( wxApp::GetComCtl32Version() >= 610 )
+    {
+        const HRESULT hr = ::SendMessage(GetHwnd(),
+                                         TVM_SETEXTENDEDSTYLE,
+                                         TVS_EX_DOUBLEBUFFER,
+                                         on ? TVS_EX_DOUBLEBUFFER : 0);
+        if ( hr == S_OK )
+        {
+            // There is no need to erase background for a double-buffered
+            // window, so disable it when enabling double buffering and restore
+            // the default background style value when disabling it.
+            SetBackgroundStyle(on ? wxBG_STYLE_PAINT : wxBG_STYLE_ERASE);
+        }
+        else
+        {
+            wxLogApiError("TreeView_SetExtendedStyle(TVS_EX_DOUBLEBUFFER)", hr);
+        }
+    }
+}
+
 wxTreeCtrl::~wxTreeCtrl()
 {
     m_isBeingDeleted = true;