Fix issue #310 - crash on export sprite sheet

The timeline wasn't being added as a Document observer, so it wasn't
getting notifications about layers modifications. In this way the timeline
wasn't able to update its m_layers[] internal field and was accessing to
removed layers/invalid memory.

src/app/document_api.cpp

@@ -632,7 +632,7 @@ void DocumentApi::removeLayer(Layer* layer)
   DocumentEvent ev(m_document);
   ev.sprite(layer->getSprite());
   ev.layer(layer);
-  m_document->notifyObservers<DocumentEvent&>(&DocumentObserver::onRemoveLayer, ev);
+  m_document->notifyObservers<DocumentEvent&>(&DocumentObserver::onBeforeRemoveLayer, ev);
 
   // Add undoers.
   if (undoEnabled())
@@ -640,6 +640,9 @@ void DocumentApi::removeLayer(Layer* layer)
 
   // Do the action.
   layer->getParent()->removeLayer(layer);
+
+  m_document->notifyObservers<DocumentEvent&>(&DocumentObserver::onAfterRemoveLayer, ev);
+
   delete layer;
 }
 

src/app/document_observer.h

@@ -41,7 +41,8 @@ namespace app {
 
     virtual void onRemoveSprite(DocumentEvent& ev) { }
 
-    virtual void onRemoveLayer(DocumentEvent& ev) { }
+    virtual void onBeforeRemoveLayer(DocumentEvent& ev) { }
+    virtual void onAfterRemoveLayer(DocumentEvent& ev) { }
 
     // Called when a frame is removed. It's called after the frame was
     // removed, and the sprite's total number of frames is modified.

src/app/ui/document_view.cpp

@@ -218,7 +218,7 @@ void DocumentView::onAddLayer(DocumentEvent& ev)
   }
 }
 
-void DocumentView::onRemoveLayer(DocumentEvent& ev)
+void DocumentView::onBeforeRemoveLayer(DocumentEvent& ev)
 {
   Sprite* sprite = ev.sprite();
   Layer* layer = ev.layer();

src/app/ui/document_view.h

@@ -64,7 +64,7 @@ namespace app {
     void onSpritePixelsModified(DocumentEvent& ev) OVERRIDE;
     void onLayerMergedDown(DocumentEvent& ev) OVERRIDE;
     void onAddLayer(DocumentEvent& ev) OVERRIDE;
-    void onRemoveLayer(DocumentEvent& ev) OVERRIDE;
+    void onBeforeRemoveLayer(DocumentEvent& ev) OVERRIDE;
     void onAddFrame(DocumentEvent& ev) OVERRIDE;
     void onRemoveFrame(DocumentEvent& ev) OVERRIDE;
     void onTotalFramesChanged(DocumentEvent& ev) OVERRIDE;

src/app/ui/timeline.cpp

@@ -180,6 +180,8 @@ void Timeline::updateUsingEditor(Editor* editor)
   DocumentView* view = m_editor->getDocumentView();
   view->getDocumentLocation(&location);
 
+  location.document()->addObserver(this);
+
   // If we are already in the same position as the "editor", we don't
   // need to update the at all timeline.
   if (m_document == location.document() &&
@@ -859,11 +861,13 @@ void Timeline::onPreferredSize(PreferredSizeEvent& ev)
 void Timeline::onPaint(ui::PaintEvent& ev)
 {
   Graphics* g = ev.getGraphics();
+  bool noDoc = (m_document == NULL);
+  if (noDoc)
+    goto paintNoDoc;
 
-  if (!m_document) {
+  try {
-    drawPart(g, getClientBounds(), NULL, m_timelinePaddingStyle);
+    // Lock the sprite to read/render it.
-    return;
+    const DocumentReader documentReader(m_document);
-  }
     
     int layer, first_layer, last_layer;
     FrameNumber frame, first_frame, last_frame;
@@ -925,6 +929,14 @@ void Timeline::onPaint(ui::PaintEvent& ev)
     }
 
     drawPaddings(g);
+  }
+  catch (const LockedDocumentException&) {
+    noDoc = true;
+  }
+
+paintNoDoc:;
+  if (noDoc)
+    drawPart(g, getClientBounds(), NULL, m_timelinePaddingStyle);
 }
 
 void Timeline::onCommandAfterExecution(Context* context)
@@ -954,7 +966,7 @@ void Timeline::onAddLayer(DocumentEvent& ev)
   invalidate();
 }
 
-void Timeline::onRemoveLayer(DocumentEvent& ev)
+void Timeline::onAfterRemoveLayer(DocumentEvent& ev)
 {
   Sprite* sprite = ev.sprite();
   Layer* layer = ev.layer();

src/app/ui/timeline.h

@@ -114,7 +114,7 @@ namespace app {
 
     // DocumentObserver impl.
     void onAddLayer(DocumentEvent& ev) OVERRIDE;
-    void onRemoveLayer(DocumentEvent& ev) OVERRIDE;
+    void onAfterRemoveLayer(DocumentEvent& ev) OVERRIDE;
     void onAddFrame(DocumentEvent& ev) OVERRIDE;
     void onRemoveFrame(DocumentEvent& ev) OVERRIDE;
 

src/base/observers.h

@@ -39,6 +39,7 @@ public:
   // collection and will be destroyed calling the T::dispose() member
   // function.
   void addObserver(observer_type* observer) {
+    ASSERT(std::find(m_observers.begin(), m_observers.end(), observer) == m_observers.end() && "You've tried to add an observer that already is in the collection");
     m_observers.push_back(observer);
   }
 
@@ -48,6 +49,9 @@ public:
     iterator it = std::find(m_observers.begin(), m_observers.end(), observer);
     if (it != end())
       m_observers.erase(it);
+    else {
+      ASSERT(false && "You've tried to remove an observer that isn't in the collection");
+    }
   }
 
   void notifyObservers(void (observer_type::*method)()) {