Fixed: Potential crash during startup

Canvas's init function may actually end up destroying the Canvas
(e.g., FSAA mode changes during the startup). Thus Canvas must take
care not to perform any more actions after calling the init callback
function.

Also updated Canvas's parent pointer appropriately when handling a
canvas recreation.

doomsday/client/include/ui/canvas.h

@@ -67,6 +67,8 @@ class Canvas : public QGLWidget
      */
     void setInitFunc(void (*canvasInitializeFunc)(Canvas&));
 
+    void setParent(CanvasWindow *parent);
+
     /**
      * Sets the callback function that is called when the window's focus state changes.
      * The callback is given @c true or @c false as argument, with

doomsday/client/src/ui/canvas.cpp

@@ -186,12 +186,10 @@ void Canvas::setInitFunc(void (*canvasInitializeFunc)(Canvas&))
     d->initCallback = canvasInitializeFunc;
 }
 
-/*
-void Canvas::setDrawFunc(void (*canvasDrawFunc)(Canvas&))
+void Canvas::setParent(CanvasWindow *parent)
 {
-    d->drawCallback = canvasDrawFunc;
+    d->parent = parent;
 }
-*/
 
 void Canvas::setFocusFunc(void (*canvasFocusChanged)(Canvas&, bool))
 {
@@ -200,7 +198,6 @@ void Canvas::setFocusFunc(void (*canvasFocusChanged)(Canvas&, bool))
 
 void Canvas::useCallbacksFrom(Canvas &other)
 {
-    //d->drawCallback = other.d->drawCallback;
     d->focusCallback = other.d->focusCallback;
 }
 
@@ -304,17 +301,25 @@ void Canvas::showEvent(QShowEvent* ev)
 
 void Canvas::notifyInit()
 {
-    if(!d->initNotified && d->initCallback)
+    if(d->initNotified) return;
+
+    d->initNotified = true;
+    if(d->parent)
     {
-        d->initNotified = true;
+        d->parent->canvasReady(*this);
+    }
 
+    if(d->initCallback)
+    {
         d->initCallback(*this);
-        d->parent->canvasReady(*this);
+        // Canvas might be destroyed now.
     }
 }
 
 void Canvas::paintGL()
 {
+    if(!d->parent) return;
+
     // The parent knows what to draw here (UI widgets).
     d->parent->paintCanvas(*this);
 

doomsday/client/src/ui/canvaswindow.cpp

@@ -196,6 +196,7 @@ void CanvasWindow::recreateCanvas()
     // We'll re-trap the mouse after the new canvas is ready.
     d->mouseWasTrapped = canvas().isMouseTrapped();
     canvas().trapMouse(false);
+    canvas().setParent(0);
 
     // Create the replacement Canvas. Once it's created and visible, we'll
     // finish the switch-over.