Add support to scroll in MovingPixelsState without calling a full dropImage().

+ Added EditorState::isTemporalState() to know if we've to do a dropImage()
  or a simple dropImageTemporarily() only.
+ Improved the return type of EditorState::onBeforeChangeState() member
  function (now it's an enum instead of a bool).

src/widgets/editor/editor.cpp

@@ -186,11 +186,12 @@ void Editor::setStateInternal(const EditorStatePtr& newState)
 
   // Fire before change state event, set the state, and fire after
   // change state event.
-  bool keepInHistory = m_state->onBeforeChangeState(this);
+  EditorState::BeforeChangeAction beforeChangeAction =
+    m_state->onBeforeChangeState(this, newState);
 
   // Push a new state
   if (newState) {
-    if (!keepInHistory)
+    if (beforeChangeAction == EditorState::DiscardState)
       m_statesHistory.pop();
 
     m_statesHistory.push(newState);
@@ -204,6 +205,8 @@ void Editor::setStateInternal(const EditorStatePtr& newState)
     m_state = m_statesHistory.top();
   }
 
+  ASSERT(m_state != NULL);
+
   // Change to the new state.
   m_state->onAfterChangeState(this);
 
@@ -239,8 +242,10 @@ void Editor::setDocument(Document* document)
   //jmanager_free_mouse();      // TODO Why is this here? Review this code
 
   // Reset all states (back to standby).
+  EditorStatePtr firstState(new StandbyState);
   m_statesHistory.clear();
-  setState(EditorStatePtr(new StandbyState));
+  m_statesHistory.push(firstState);
+  setState(firstState);
 
   if (m_cursor_thick)
     editor_clean_cursor();

src/widgets/editor/editor_state.h

@@ -34,13 +34,24 @@ union Message;
 class EditorState
 {
 public:
+  enum BeforeChangeAction {
+    DiscardState,
+    KeepState
+  };
+
   EditorState() { }
   virtual ~EditorState() { }
 
+  // Returns true if this state is a "temporal" state. It means that
+  // this state doesn't go to other state than the previous one.
+  virtual bool isTemporalState() const { return false; }
+
   // Called just before this state is replaced by a new state in the
   // Editor::setState() method.  Returns true if this state should be
   // kept in the EditorStatesHistory.
-  virtual bool onBeforeChangeState(Editor* editor) { return true; }
+  virtual BeforeChangeAction onBeforeChangeState(Editor* editor, EditorState* newState) {
+    return KeepState;
+  }
 
   // Called when this instance is set as the new Editor's state when
   // Editor::setState() method is used.

src/widgets/editor/moving_pixels_state.cpp

@@ -35,6 +35,7 @@
 #include "widgets/editor/editor.h"
 #include "widgets/editor/editor_customization_delegate.h"
 #include "widgets/editor/pixels_movement.h"
+#include "widgets/editor/scrolling_state.h"
 #include "widgets/editor/standby_state.h"
 #include "widgets/editor/transform_handles.h"
 #include "widgets/statebar.h"
@@ -73,7 +74,7 @@ MovingPixelsState::~MovingPixelsState()
   delete m_pixelsMovement;
 }
 
-bool MovingPixelsState::onBeforeChangeState(Editor* editor)
+EditorState::BeforeChangeAction MovingPixelsState::onBeforeChangeState(Editor* editor, EditorState* newState)
 {
   ASSERT(m_pixelsMovement != NULL);
 
@@ -81,18 +82,25 @@ bool MovingPixelsState::onBeforeChangeState(Editor* editor)
   if (m_pixelsMovement->isDragging())
     m_pixelsMovement->dropImageTemporarily();
 
-  // Drop pixels if the user press a button outside the selection
-  m_pixelsMovement->dropImage();
+  // Drop pixels if we are changing to a non-temporary state (a
+  // temporary state is something like ScrollingState).
+  if (!newState || !newState->isTemporalState()) {
+    m_pixelsMovement->dropImage();
 
-  editor->getDocument()->resetTransformation();
+    editor->getDocument()->resetTransformation();
 
-  delete m_pixelsMovement;
-  m_pixelsMovement = NULL;
+    delete m_pixelsMovement;
+    m_pixelsMovement = NULL;
 
-  editor->releaseMouse();
+    editor->releaseMouse();
 
-  app_get_statusbar()->hideMovePixelsOptions();
-  return false;                 // Don't keep this state in history
+    app_get_statusbar()->hideMovePixelsOptions();
+    return DiscardState;
+  }
+  else {
+    editor->releaseMouse();
+    return KeepState;
+  }
 }
 
 void MovingPixelsState::onCurrentToolChange(Editor* editor)
@@ -118,6 +126,13 @@ bool MovingPixelsState::onMouseDown(Editor* editor, Message* msg)
   Decorator* decorator = static_cast<Decorator*>(editor->getDecorator());
   Document* document = editor->getDocument();
 
+  // Start scroll loop
+  if (msg->mouse.middle) { // TODO raw msg->mouse.middle here, this should be customizable
+    editor->setState(EditorStatePtr(new ScrollingState()));
+    editor->captureMouse();
+    return true;
+  }
+
   // Transform selected pixels
   if (document->isMaskVisible() &&
       decorator->getTransformHandles(editor)) {
@@ -316,7 +331,7 @@ void MovingPixelsState::setTransparentColor(const Color& color)
 void MovingPixelsState::dropPixels(Editor* editor)
 {
   // Just change to default state (StandbyState generally). We'll
-  // receive an onBeforeChangeState event after this call.
+  // receive an onBeforeChangeState() event after this call.
   editor->backToPreviousState();
 }
 

src/widgets/editor/moving_pixels_state.h

@@ -34,7 +34,7 @@ public:
   MovingPixelsState(Editor* editor, Message* msg, PixelsMovement* pixelsMovement, HandleType handle);
   virtual ~MovingPixelsState();
 
-  virtual bool onBeforeChangeState(Editor* editor) OVERRIDE;
+  virtual BeforeChangeAction onBeforeChangeState(Editor* editor, EditorState* newState) OVERRIDE;
   virtual void onCurrentToolChange(Editor* editor) OVERRIDE;
   virtual bool onMouseDown(Editor* editor, Message* msg) OVERRIDE;
   virtual bool onMouseUp(Editor* editor, Message* msg) OVERRIDE;

src/widgets/editor/scrolling_state.h

@@ -27,6 +27,7 @@ class ScrollingState : public EditorState
 public:
   ScrollingState();
   virtual ~ScrollingState();
+  virtual bool isTemporalState() const OVERRIDE { return true; }
   virtual bool onMouseDown(Editor* editor, Message* msg) OVERRIDE;
   virtual bool onMouseUp(Editor* editor, Message* msg) OVERRIDE;
   virtual bool onMouseMove(Editor* editor, Message* msg) OVERRIDE;

src/widgets/editor/standby_state.cpp

@@ -133,7 +133,7 @@ bool StandbyState::onMouseDown(Editor* editor, Message* msg)
   context->setActiveDocument(document);
 
   // Start scroll loop
-  if (msg->mouse.middle || clicked_ink->isScrollMovement()) {
+  if (msg->mouse.middle || clicked_ink->isScrollMovement()) { // TODO raw msg->mouse.middle here, this should be customizable
     editor->setState(EditorStatePtr(new ScrollingState()));
     editor->captureMouse();
     return true;