Fix bug keeping the modified range different than the visible range when moving pixels

When we clicked the current cel/frame/layer on MovingPixelsState in
the Timeline, we weren't dropping the pixels, so the range was
different in the Timeline UI, but we were using the old site range
which was different (bigger) than the Timeline range.

Fixes several bugs: https://community.aseprite.org/t/8618

src/app/ui/editor/moving_pixels_state.cpp

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -35,6 +35,7 @@
 #include "app/ui/keyboard_shortcuts.h"
 #include "app/ui/main_window.h"
 #include "app/ui/status_bar.h"
+#include "app/ui/timeline/timeline.h"
 #include "app/ui_context.h"
 #include "app/util/clipboard.h"
 #include "app/util/layer_utils.h"
@@ -113,10 +114,14 @@ MovingPixelsState::MovingPixelsState(Editor* editor, MouseMessage* msg, PixelsMo
   ContextBar* contextBar = App::instance()->contextBar();
   contextBar->updateForMovingPixels();
   contextBar->add_observer(this);
+
+  App::instance()->mainWindow()->getTimeline()->add_observer(this);
 }
 
 MovingPixelsState::~MovingPixelsState()
 {
+  App::instance()->mainWindow()->getTimeline()->remove_observer(this);
+
   ContextBar* contextBar = App::instance()->contextBar();
   contextBar->remove_observer(this);
   contextBar->updateForActiveTool();
@@ -712,6 +717,15 @@ void MovingPixelsState::onBeforeLayerChanged(Editor* editor)
     dropPixels();
 }
 
+void MovingPixelsState::onBeforeRangeChanged(Timeline* timeline)
+{
+  if (!isActiveDocument())
+    return;
+
+  if (m_pixelsMovement)
+    dropPixels();
+}
+
 void MovingPixelsState::onTransparentColorChange()
 {
   ASSERT(m_pixelsMovement);

src/app/ui/editor/moving_pixels_state.h

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This program is distributed under the terms of
@@ -15,6 +15,7 @@
 #include "app/ui/editor/pixels_movement.h"
 #include "app/ui/editor/standby_state.h"
 #include "app/ui/status_bar.h"
+#include "app/ui/timeline/timeline_observer.h"
 #include "obs/connection.h"
 #include "ui/timer.h"
 
@@ -29,6 +30,7 @@ namespace app {
   class MovingPixelsState
     : public StandbyState
     , EditorObserver
+    , TimelineObserver
     , ContextBarObserver {
   public:
     MovingPixelsState(Editor* editor, ui::MouseMessage* msg, PixelsMovementPtr pixelsMovement, HandleType handle);
@@ -63,6 +65,9 @@ namespace app {
     virtual void onBeforeFrameChanged(Editor* editor) override;
     virtual void onBeforeLayerChanged(Editor* editor) override;
 
+    // TimelineObserver
+    virtual void onBeforeRangeChanged(Timeline* timeline) override;
+
     // ContextBarObserver
     virtual void onDropPixels(ContextBarObserver::DropAction action) override;
 

src/app/ui/timeline/timeline.cpp

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -3889,6 +3889,8 @@ void Timeline::invalidateRange()
 void Timeline::clearAndInvalidateRange()
 {
   if (m_range.enabled()) {
+    notify_observers(&TimelineObserver::onBeforeRangeChanged, this);
+
     invalidateRange();
     m_range.clearRange();
   }

src/app/ui/timeline/timeline.h

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -10,19 +10,21 @@
 #pragma once
 
 #include "app/doc_observer.h"
-#include "app/docs_observer.h"
 #include "app/doc_range.h"
+#include "app/docs_observer.h"
 #include "app/loop_tag.h"
 #include "app/pref/preferences.h"
 #include "app/ui/editor/editor_observer.h"
 #include "app/ui/input_chain_element.h"
 #include "app/ui/timeline/ani_controls.h"
+#include "app/ui/timeline/timeline_observer.h"
 #include "doc/frame.h"
 #include "doc/layer.h"
 #include "doc/selected_frames.h"
 #include "doc/selected_layers.h"
 #include "doc/sprite.h"
 #include "obs/connection.h"
+#include "obs/observable.h"
 #include "ui/scroll_bar.h"
 #include "ui/timer.h"
 #include "ui/widget.h"
@@ -57,6 +59,7 @@ namespace app {
 
   class Timeline : public ui::Widget,
                    public ui::ScrollableViewDelegate,
+                   public obs::observable<TimelineObserver>,
                    public ContextObserver,
                    public DocsObserver,
                    public DocObserver,