Fix painting logic in wxQt wxClientDC implementation

The original drawing mechanism was generating lots of QWarning messages
when running samples (e.g. htlbox, caret, etc.) and in some cases was
not actually completely drawing every element of the sample. The issue
was that the QPicture was being shared incorrectly between wxWindow and
wxClientDC and attempts to start painting, update, etc. were generating
console warnings.

Closes https://github.com/wxWidgets/wxWidgets/pull/1152

include/wx/qt/dcclient.h

@@ -10,6 +10,10 @@
 
 #include "wx/qt/dc.h"
 
+#include "wx/scopedptr.h"
+
+class QPicture;
+
 class WXDLLIMPEXP_CORE wxWindowDCImpl : public wxQtDCImpl
 {
 public:
@@ -35,6 +39,8 @@ public:
 
     ~wxClientDCImpl();
 private:
+    wxScopedPtr<QPicture> m_pict;
+
     wxDECLARE_CLASS(wxClientDCImpl);
     wxDECLARE_NO_COPY_CLASS(wxClientDCImpl);
 };

include/wx/qt/window.h

@@ -145,7 +145,8 @@ public:
 
     // wxQt implementation internals:
 
-    virtual QPicture *QtGetPicture() const;
+    // Caller maintains ownership of pict - window will NOT delete it
+    void QtSetPicture( QPicture* pict );
 
     QPainter *QtGetPainter();
 

src/qt/dcclient.cpp

@@ -27,6 +27,30 @@
 
 //##############################################################################
 
+namespace
+{
+class QtPictureSetter
+{
+public:
+    QtPictureSetter(wxWindow *window, QPicture *pict)
+        : m_window( window )
+    {
+        m_window->QtSetPicture( pict );
+    }
+
+    ~QtPictureSetter()
+    {
+        m_window->QtSetPicture( NULL );
+    }
+
+private:
+    wxWindow* const m_window;
+
+    wxDECLARE_NO_COPY_CLASS(QtPictureSetter);
+};
+}
+
+
 wxIMPLEMENT_CLASS(wxWindowDCImpl,wxQtDCImpl);
 
 wxWindowDCImpl::wxWindowDCImpl( wxDC *owner )
@@ -54,7 +78,7 @@ wxWindowDCImpl::~wxWindowDCImpl()
     }
     if ( m_window )
     {
-        // do not destroy as it is owned by the window
+        // do not destroy in base class as it is owned by the window
         m_qtPainter = NULL;
     }
 }
@@ -67,6 +91,7 @@ wxClientDCImpl::wxClientDCImpl( wxDC *owner )
     : wxWindowDCImpl( owner )
 {
     m_window = NULL;
+    m_qtPainter = NULL;
 }
 
 wxClientDCImpl::wxClientDCImpl( wxDC *owner, wxWindow *win )
@@ -74,8 +99,11 @@ wxClientDCImpl::wxClientDCImpl( wxDC *owner, wxWindow *win )
 {
     m_window = win;
 
-    QPicture *pic = win->QtGetPicture();
+    m_qtPainter = new QPainter();
-    m_ok = m_qtPainter->begin( pic );
+
+    m_pict.reset(new QPicture());
+    m_ok = m_qtPainter->begin( m_pict.get() );
+
     QtPreparePainter();
 }
 
@@ -88,10 +116,11 @@ wxClientDCImpl::~wxClientDCImpl()
     {
         m_qtPainter->end();
         m_ok = false;
-        QPicture *pict = m_window->QtGetPicture();
 
         if ( m_window != NULL )
         {
+            QtPictureSetter pictureSetter(m_window, m_pict.get());
+
             // get the inner widget in scroll areas:
             QWidget *widget;
             if ( m_window->QtGetScrollBarsContainer() )
@@ -102,8 +131,8 @@ wxClientDCImpl::~wxClientDCImpl()
             }
             // force paint event if there is something to replay and
             // if not currently inside a paint event (to avoid recursion)
-            QRect rect = pict->boundingRect();
+            QRect rect = m_pict->boundingRect();
-            if ( !pict->isNull() && !widget->paintingActive() && !rect.isEmpty() )
+            if ( !m_pict->isNull() && !widget->paintingActive() && !rect.isEmpty() )
             {
                 // only force the update of the rect affected by the DC
                 widget->update( rect );
@@ -111,12 +140,15 @@ wxClientDCImpl::~wxClientDCImpl()
             else
             {
                 // Not drawing anything, reset picture to avoid issues in handler
-                pict->setData( NULL, 0 );
+                m_pict->setData( NULL, 0 );
             }
+
             // let destroy the m_qtPainter (see inherited classes destructors)
             m_window = NULL;
         }
     }
+
+    // Painter will be deleted by base class
 }
 
 //##############################################################################

src/qt/window.cpp

@@ -210,7 +210,7 @@ void wxWindowQt::Init()
     m_horzScrollBar = NULL;
     m_vertScrollBar = NULL;
 
-    m_qtPicture = new QPicture();
+    m_qtPicture = NULL;
     m_qtPainter = new QPainter();
 
     m_mouseInside = false;
@@ -251,7 +251,6 @@ wxWindowQt::~wxWindowQt()
 
     DestroyChildren(); // This also destroys scrollbars
 
-    delete m_qtPicture;
     delete m_qtPainter;
 
 #if wxUSE_ACCEL
@@ -1126,7 +1125,7 @@ bool wxWindowQt::QtHandlePaintEvent ( QWidget *handler, QPaintEvent *event )
         {
             bool handled;
 
-            if ( m_qtPicture->isNull() )
+            if ( m_qtPicture == NULL )
             {
                 // Real paint event (not for wxClientDC), prepare the background
                 switch ( GetBackgroundStyle() )
@@ -1558,9 +1557,9 @@ QScrollArea *wxWindowQt::QtGetScrollBarsContainer() const
     return m_qtContainer;
 }
 
-QPicture *wxWindowQt::QtGetPicture() const
+void wxWindowQt::QtSetPicture( QPicture* pict )
 {
-    return m_qtPicture;
+    m_qtPicture = pict;
 }
 
 QPainter *wxWindowQt::QtGetPainter()