From 9e314a257d2e388aa4eada0cbf9761d3f97b9160 Mon Sep 17 00:00:00 2001
From: Rodney <rodney.baker@gmail.com>
Date: Jan 20 2023 13:32:39 +0000
Subject: Merge pull request #4712 from shun-iwasawa/c/enhance_viewer_preview


Viewer preview feature enhancement
---

diff --git a/toonz/sources/include/toonzqt/flipconsole.h b/toonz/sources/include/toonzqt/flipconsole.h
index 7746360..19967a5 100644
--- a/toonz/sources/include/toonzqt/flipconsole.h
+++ b/toonz/sources/include/toonzqt/flipconsole.h
@@ -276,6 +276,7 @@ public:
     setChecked(button, !isChecked(button));
   }
   void setStopAt(int frame);
+  void setStartAt(int frame);
 
   // the main (currently the only) use for current flipconsole and setActive is
   // to
@@ -356,6 +357,8 @@ private:
   int m_from, m_to, m_step;
   int m_currentFrame, m_framesCount;
   int m_stopAt = -1;
+  int m_startAt =
+      -1;  // used in the "play selection" mode of the viewer preview
   ImagePainter::VisualSettings m_settings;
 
   bool m_isPlay;
diff --git a/toonz/sources/toonz/mainwindow.cpp b/toonz/sources/toonz/mainwindow.cpp
index 8189a51..e387677 100644
--- a/toonz/sources/toonz/mainwindow.cpp
+++ b/toonz/sources/toonz/mainwindow.cpp
@@ -467,6 +467,9 @@ centralWidget->setLayout(centralWidgetLayout);*/
   if (TSystem::doesExistFileOrLevel(TFilePath(ffmpegCachePath))) {
     TSystem::rmDirTree(TFilePath(ffmpegCachePath));
   }
+
+  connect(TApp::instance(), SIGNAL(activeViewerChanged()), this,
+          SLOT(onActiveViewerChanged()));
 }
 
 //-----------------------------------------------------------------------------
@@ -1319,6 +1322,27 @@ void MainWindow::onUpdateCheckerDone(bool error) {
   disconnect(m_updateChecker);
   m_updateChecker->deleteLater();
 }
+
+//-----------------------------------------------------------------------------
+
+void MainWindow::onActiveViewerChanged() {
+  // sync the command state to the button state of the activated viewer
+  SceneViewer *activeViewer = TApp::instance()->getActiveViewer();
+  if (!activeViewer) return;
+  BaseViewerPanel *bvp = qobject_cast<BaseViewerPanel *>(
+      activeViewer->parentWidget()->parentWidget());
+  if (!bvp) return;
+  bool prev, subCamPrev;
+  bvp->getPreviewButtonStates(prev, subCamPrev);
+
+  CommandManager::instance()
+      ->getAction(MI_ToggleViewerPreview)
+      ->setChecked(prev);
+  CommandManager::instance()
+      ->getAction(MI_ToggleViewerSubCameraPreview)
+      ->setChecked(subCamPrev);
+}
+
 //-----------------------------------------------------------------------------
 
 void MainWindow::closeEvent(QCloseEvent *event) {
@@ -2056,6 +2080,12 @@ void MainWindow::defineActions() {
   createMenuRenderAction(MI_SavePreviewedFrames,
                          QT_TR_NOOP("&Save Previewed Frames"), "",
                          "save_previewed_frames");
+  createToggle(MI_ToggleViewerPreview, QT_TR_NOOP("Toggle Viewer Preview"), "",
+               false, MenuRenderCommandType, "pane_preview");
+  createToggle(MI_ToggleViewerSubCameraPreview,
+               QT_TR_NOOP("Toggle Viewer Sub-camera Preview"), "", false,
+               MenuRenderCommandType, "pane_subpreview");
+
   createRightClickMenuAction(MI_OpenPltGizmo, QT_TR_NOOP("&Palette Gizmo"), "",
                              "palettegizmo");
   createRightClickMenuAction(MI_EraseUnusedStyles,
@@ -2823,7 +2853,7 @@ void MainWindow::defineActions() {
   createToolOptionsAction("A_ToolOption_RotateRight",
                           QT_TR_NOOP("Rotate Selection/Object Right"), "");
 
-// Visualization
+  // Visualization
 
   createViewerAction(V_ZoomIn, QT_TR_NOOP("Zoom In"), "+");
   createViewerAction(V_ZoomOut, QT_TR_NOOP("Zoom Out"), "-");
diff --git a/toonz/sources/toonz/mainwindow.h b/toonz/sources/toonz/mainwindow.h
index 865d0c5..8a87855 100644
--- a/toonz/sources/toonz/mainwindow.h
+++ b/toonz/sources/toonz/mainwindow.h
@@ -221,6 +221,7 @@ protected slots:
   void onInk1CheckTriggered(bool on);
 
   void onUpdateCheckerDone(bool);
+  void onActiveViewerChanged();
 
 public slots:
   /*--- タイトルにシーン名を入れる ---*/
diff --git a/toonz/sources/toonz/menubarcommandids.h b/toonz/sources/toonz/menubarcommandids.h
index b749dee..11fe2fe 100644
--- a/toonz/sources/toonz/menubarcommandids.h
+++ b/toonz/sources/toonz/menubarcommandids.h
@@ -55,6 +55,8 @@
 #define MI_FreezePreview "MI_FrezzePreview"
 #define MI_SavePreviewedFrames "MI_SavePreviewedFrames"
 // #define MI_SavePreview         "MI_SavePreview"
+#define MI_ToggleViewerPreview "MI_ToggleViewerPreview"
+#define MI_ToggleViewerSubCameraPreview "MI_ToggleViewerSubCameraPreview"
 #define MI_Print "MI_Print"
 #define MI_Preferences "MI_Preferences"
 #define MI_SavePreset "MI_SavePreset"
diff --git a/toonz/sources/toonz/pane.cpp b/toonz/sources/toonz/pane.cpp
index d6a6243..2f2662f 100644
--- a/toonz/sources/toonz/pane.cpp
+++ b/toonz/sources/toonz/pane.cpp
@@ -37,6 +37,7 @@
 #include <QScreen>
 
 extern TEnv::StringVar EnvSafeAreaName;
+extern TEnv::IntVar EnvViewerPreviewBehavior;
 
 //=============================================================================
 // TPanel
@@ -411,6 +412,58 @@ void TPanelTitleBarButtonForSafeArea::onSetSafeArea() {
 //-----------------------------------------------------------------------------
 
 //=============================================================================
+// TPanelTitleBarButtonForPreview
+//-----------------------------------------------------------------------------
+
+void TPanelTitleBarButtonForPreview::mousePressEvent(QMouseEvent *e) {
+  if (e->button() != Qt::RightButton) {
+    m_pressed = !m_pressed;
+    emit toggled(m_pressed);
+    update();
+  }
+}
+
+//-----------------------------------------------------------------------------
+
+void TPanelTitleBarButtonForPreview::contextMenuEvent(QContextMenuEvent *e) {
+  QMenu menu(this);
+
+  // 0: current frame
+  // 1: all frames in the preview range
+  // 2: selected cell, auto play once & stop
+  QStringList behaviorsStrList = {tr("Current frame"),
+                                  tr("All preview range frames"),
+                                  tr("Selected cells - Auto play")};
+
+  QActionGroup *behaviorGroup = new QActionGroup(this);
+
+  for (int i = 0; i < behaviorsStrList.size(); i++) {
+    QAction *action = menu.addAction(behaviorsStrList.at(i));
+    action->setData(i);
+    connect(action, SIGNAL(triggered()), this, SLOT(onSetPreviewBehavior()));
+    action->setCheckable(true);
+    behaviorGroup->addAction(action);
+    if (i == EnvViewerPreviewBehavior) action->setChecked(true);
+  }
+
+  menu.exec(e->globalPos());
+}
+
+//-----------------------------------------------------------------------------
+
+void TPanelTitleBarButtonForPreview::onSetPreviewBehavior() {
+  int behaviorId = qobject_cast<QAction *>(sender())->data().toInt();
+  // change safearea if the different one is selected
+  if (EnvViewerPreviewBehavior != behaviorId) {
+    EnvViewerPreviewBehavior = behaviorId;
+    // emit sceneChanged without setting dirty flag
+    TApp::instance()->getCurrentScene()->notifySceneChanged(false);
+  }
+}
+
+//-----------------------------------------------------------------------------
+
+//=============================================================================
 // TPanelTitleBarButtonSet
 //-----------------------------------------------------------------------------
 
diff --git a/toonz/sources/toonz/pane.h b/toonz/sources/toonz/pane.h
index 6cd40bc..fb809db 100644
--- a/toonz/sources/toonz/pane.h
+++ b/toonz/sources/toonz/pane.h
@@ -5,7 +5,7 @@
 
 // TODO: cambiare il nome del file in tpanel.h
 
-//#include <QDockWidget>
+// #include <QDockWidget>
 #include "../toonzqt/tdockwindows.h"
 
 class TPanelTitleBarButtonSet;
@@ -68,7 +68,7 @@ signals:
 };
 
 //-----------------------------------------------------------------------------
-/*! specialized button for sage area which enables to choose safe area size by
+/*! specialized button for safe area which enables to choose safe area size by
  * context menu
  */
 
@@ -88,6 +88,27 @@ protected slots:
 };
 
 //-----------------------------------------------------------------------------
+/*! specialized button for safe area which enables to choose safe area size by
+ * context menu
+ */
+
+class TPanelTitleBarButtonForPreview final : public TPanelTitleBarButton {
+  Q_OBJECT
+public:
+  TPanelTitleBarButtonForPreview(QWidget *parent,
+                                 const QString &standardPixmapName)
+      : TPanelTitleBarButton(parent, standardPixmapName) {}
+
+  bool isChecked() { return m_pressed; }
+
+protected:
+  void contextMenuEvent(QContextMenuEvent *event) override;
+  void mousePressEvent(QMouseEvent *event) override;
+protected slots:
+  void onSetPreviewBehavior();
+};
+
+//-----------------------------------------------------------------------------
 
 //! a buttonset can group different TPanelTitleBarButton
 class TPanelTitleBarButtonSet final : public QObject {
diff --git a/toonz/sources/toonz/previewer.cpp b/toonz/sources/toonz/previewer.cpp
index 7192ebe..8ec40c6 100644
--- a/toonz/sources/toonz/previewer.cpp
+++ b/toonz/sources/toonz/previewer.cpp
@@ -196,6 +196,9 @@ public:
   // are assumed correct.
   void refreshFrame(int frame);
 
+  void addRenderData(std::vector<TRenderer::RenderData> &datas, int frame);
+  void addFramesToRenderQueue(const std::vector<int> frames);
+
   // TRenderPort methods
   void onRenderRasterStarted(const RenderData &renderData) override;
   void onRenderRasterCompleted(const RenderData &renderData) override;
@@ -709,21 +712,33 @@ void Previewer::Imp::doOnRenderRasterCompleted(const RenderData &renderData) {
       it->second
           .m_rectUnderRender);  // Extract may MODIFY IT! E.g. with shrinks..!
   cachedRas = cachedRas->extract(rectUnderRender);
+
   if (cachedRas) {
     cachedRas->copy(ras);
-    TImageCache::instance()->add(str, ri);
   }
 
-  // Update the FrameInfo
-  it->second.m_renderedRegion += toQRect(it->second.m_rectUnderRender);
-  it->second.m_rectUnderRender = TRect();
+  // Submit the image to the cache, for all cluster's frames
+  unsigned int i, size = renderData.m_frames.size();
+  for (i = 0; i < size; ++i) {
+    int f                                   = renderData.m_frames[i];
+    std::map<int, FrameInfo>::iterator f_it = m_frames.find(f);
+    if (f_it == m_frames.end()) continue;
 
-  // Update the progress bar status
-  if (frame < m_pbStatus.size())
-    m_pbStatus[frame] = FlipSlider::PBFrameFinished;
+    if (cachedRas) {
+      std::string f_str = m_cachePrefix + std::to_string(f);
+      TImageCache::instance()->add(f_str, ri);
+    }
 
-  // Notify listeners
-  notifyCompleted(frame);
+    // Update the FrameInfo
+    f_it->second.m_renderedRegion += toQRect(f_it->second.m_rectUnderRender);
+    f_it->second.m_rectUnderRender = TRect();
+
+    // Update the progress bar status
+    if (f < m_pbStatus.size()) m_pbStatus[f] = FlipSlider::PBFrameFinished;
+
+    // Notify listeners
+    notifyCompleted(f);
+  }
 }
 
 //-----------------------------------------------------------------------------
@@ -980,6 +995,69 @@ void Previewer::Imp::saveFrame() {
   savedFrames          = 0;
 }
 
+//-----------------------------------------------------------------------------
+
+void Previewer::Imp::addRenderData(std::vector<TRenderer::RenderData> &datas,
+                                   int frame) {
+  // Build the TFxPair to be passed to TRenderer
+  TFxPair fxPair = buildSceneFx(frame);
+
+  // Update the RenderInfos associated with frame
+  m_frames[frame].m_rectUnderRender = m_previewRect;
+  m_frames[frame].m_alias = fxPair.m_frameA->getAlias(frame, m_renderSettings);
+  if (fxPair.m_frameB)
+    m_frames[frame].m_alias =
+        m_frames[frame].m_alias +
+        fxPair.m_frameB->getAlias(frame, m_renderSettings);
+
+  // Retrieve the renderId of the rendering instance
+  m_frames[frame].m_renderId = m_renderer.nextRenderId();
+  std::string contextName("P");
+  contextName += m_subcamera ? "SC" : "FU";
+  contextName += std::to_string(frame);
+  TPassiveCacheManager::instance()->setContextName(m_frames[frame].m_renderId,
+                                                   contextName);
+
+  datas.push_back(TRenderer::RenderData(frame, m_renderSettings, fxPair));
+}
+
+//-----------------------------------------------------------------------------
+
+void Previewer::Imp::addFramesToRenderQueue(const std::vector<int> frames) {
+  if (suspendedRendering) return;
+  // Build the region to render
+  updatePreviewRect();
+  if (m_previewRect.getLx() <= 0 || m_previewRect.getLy() <= 0) return;
+
+  RenderDataVector *renderDatas = new RenderDataVector;
+
+  for (const auto &f : frames) {
+    std::map<int, FrameInfo>::iterator it = m_frames.find(f);
+    if (it == m_frames.end()) {
+      it = m_frames.insert(std::make_pair(f, FrameInfo())).first;
+      // In case the frame is not in the frame range, we add a temporary
+      // supplement
+      // to the progress bar.
+      if (f >= (int)m_pbStatus.size()) m_pbStatus.resize(f + 1);
+      addRenderData(*renderDatas, f);
+    } else if (f < m_pbStatus.size() &&
+               m_pbStatus[f] == FlipSlider::PBFrameNotStarted) {
+      // In case the rect we would render is contained in the frame's rendered
+      // region, quit
+      if (::contains(it->second.m_renderedRegion, m_previewRect)) return;
+      // Then, check the m_previewRect against the frame's m_rectUnderRendering.
+      // Ensure that we're not re-launching the very same render.
+      if (it->second.m_rectUnderRender == m_previewRect) return;
+      // Stop any frame's previously running render process
+      m_renderer.abortRendering(it->second.m_renderId);
+      addRenderData(*renderDatas, f);
+    }
+  }
+
+  // Finally, start rendering all frames which were not found in cache
+  m_renderer.startRendering(renderDatas);
+}
+
 //=============================================================================
 // Previewer
 //-----------------------------------------------------------------------------
@@ -1141,8 +1219,8 @@ void Previewer::saveRenderedFrames() {
 
 //-----------------------------------------------------------------------------
 
-/*! Restituisce un puntatore al raster randerizzato se il frame e' disponibile,
-    altrimenti comincia a calcolarlo*/
+/*! Returns a pointer to the rendered raster if the frame is available,
+    otherwise start calculating it */
 TRasterP Previewer::getRaster(int frame, bool renderIfNeeded) const {
   if (frame < 0) return TRasterP();
   std::map<int, Imp::FrameInfo>::iterator it = m_imp->m_frames.find(frame);
@@ -1187,6 +1265,13 @@ TRasterP Previewer::getRaster(int frame, bool renderIfNeeded) const {
 
 //-----------------------------------------------------------------------------
 
+void Previewer::addFramesToRenderQueue(const std::vector<int> frames) const {
+  if (suspendedRendering) return;
+  m_imp->addFramesToRenderQueue(frames);
+}
+
+//-----------------------------------------------------------------------------
+
 //! Verifica se \b frame e' nella cache, cioe' se il frame e' disponibile
 bool Previewer::isFrameReady(int frame) const {
   if (frame < 0 || frame >= (int)m_imp->m_pbStatus.size()) return false;
diff --git a/toonz/sources/toonz/previewer.h b/toonz/sources/toonz/previewer.h
index 566d77b..6cb270e 100644
--- a/toonz/sources/toonz/previewer.h
+++ b/toonz/sources/toonz/previewer.h
@@ -70,6 +70,7 @@ public:
   void removeListener(Listener *);
 
   TRasterP getRaster(int frame, bool renderIfNeeded = true) const;
+  void addFramesToRenderQueue(const std::vector<int> frames) const;
   bool isFrameReady(int frame) const;
 
   bool doSaveRenderedFrames(TFilePath fp);
diff --git a/toonz/sources/toonz/sceneviewer.cpp b/toonz/sources/toonz/sceneviewer.cpp
index 7a77705..ee9360a 100644
--- a/toonz/sources/toonz/sceneviewer.cpp
+++ b/toonz/sources/toonz/sceneviewer.cpp
@@ -14,6 +14,8 @@
 #if defined(x64)
 #include "../stopmotion/stopmotion.h"
 #endif
+#include "tenv.h"
+#include "cellselection.h"
 
 // TnzTools includes
 #include "tools/cursors.h"
@@ -61,6 +63,7 @@
 #include "toonz/toonzimageutils.h"
 #include "toonz/txshleveltypes.h"
 #include "subcameramanager.h"
+#include "toutputproperties.h"
 
 // TnzCore includes
 #include "tpalette.h"
@@ -93,6 +96,11 @@
 void drawSpline(const TAffine &viewMatrix, const TRect &clipRect, bool camera3d,
                 double pixelSize);
 
+// 0: current frame
+// 1: all frames in the preview range
+// 2: selected cell, auto play once & stop
+TEnv::IntVar EnvViewerPreviewBehavior("ViewerPreviewBehavior", 0);
+
 //-------------------------------------------------------------------------------
 namespace {
 
@@ -950,16 +958,47 @@ void SceneViewer::enablePreview(int previewMode) {
     Previewer::instance(m_previewMode == SUBCAMERA_PREVIEW)
         ->removeListener(this);
 
+  m_previewMode = previewMode;
+
   // Schedule as a listener to Previewer.
-  if (previewMode != NO_PREVIEW) {
+  if (m_previewMode != NO_PREVIEW) {
     Previewer *previewer =
-        Previewer::instance(previewMode == SUBCAMERA_PREVIEW);
+        Previewer::instance(m_previewMode == SUBCAMERA_PREVIEW);
+
     previewer->addListener(this);
+    // 0: current frame
+    // 1: all frames in the preview range
+    // 2: selected cell, auto play once & stop
+    if (EnvViewerPreviewBehavior == 1) {
+      int r0, r1, step;
+      ToonzScene *scene = app->getCurrentScene()->getScene();
+      scene->getProperties()->getPreviewProperties()->getRange(r0, r1, step);
+      if (r0 > r1) {
+        r0 = 0;
+        r1 = scene->getFrameCount() - 1;
+      }
+      int currentFrame = app->getCurrentFrame()->getFrame();
+      std::vector<int> queueFrames;
+      for (int f = currentFrame; f <= r1; f += step) queueFrames.push_back(f);
+      for (int f = r0; f < currentFrame; f += step) queueFrames.push_back(f);
+
+      previewer->addFramesToRenderQueue(queueFrames);
+    } else if (EnvViewerPreviewBehavior == 2) {
+      TCellSelection *cellSel =
+          dynamic_cast<TCellSelection *>(TSelection::getCurrent());
+      if (cellSel && !cellSel->isEmpty()) {
+        int r0, c0, r1, c1;
+        cellSel->getSelectedCells(r0, c0, r1, c1);
+        if (r0 < r1) {
+          std::vector<int> queueFrames;
+          for (int f = r0; f <= r1; f++) queueFrames.push_back(f);
+          previewer->addFramesToRenderQueue(queueFrames);
+        }
+      }
+    }
     previewer->update();
   }
 
-  m_previewMode = previewMode;
-
   GLInvalidateAll();
 
   // for updating the title bar
@@ -1025,7 +1064,8 @@ void SceneViewer::showEvent(QShowEvent *) {
   m_visualSettings.m_sceneProperties =
       TApp::instance()->getCurrentScene()->getScene()->getProperties();
 
-  // If the viewer is hidden and preview is activated, remove the listener from preview
+  // If the viewer is hidden and preview is activated, remove the listener from
+  // preview
   if (m_previewMode != NO_PREVIEW)
     Previewer::instance(m_previewMode == SUBCAMERA_PREVIEW)->addListener(this);
 
@@ -1035,7 +1075,7 @@ void SceneViewer::showEvent(QShowEvent *) {
   bool ret = connect(sceneHandle, SIGNAL(sceneSwitched()), this,
                      SLOT(resetSceneViewer()));
   ret      = ret && connect(sceneHandle, SIGNAL(sceneChanged()), this,
-                       SLOT(onSceneChanged()));
+                            SLOT(onSceneChanged()));
   ret = ret && connect(sceneHandle, SIGNAL(preferenceChanged(const QString &)),
                        this, SLOT(onPreferenceChanged(const QString &)));
 
@@ -1112,7 +1152,8 @@ void SceneViewer::showEvent(QShowEvent *) {
 //-----------------------------------------------------------------------------
 
 void SceneViewer::hideEvent(QHideEvent *) {
-  // If the viewer is hidden and preview is activated, remove the listener from preview
+  // If the viewer is hidden and preview is activated, remove the listener from
+  // preview
   if (m_previewMode != NO_PREVIEW)
     Previewer::instance(m_previewMode == SUBCAMERA_PREVIEW)
         ->removeListener(this);
@@ -1856,7 +1897,7 @@ static void drawFpsGraph(int t0, int t1) {
 
 //-----------------------------------------------------------------------------
 
-//#define FPS_HISTOGRAM
+// #define FPS_HISTOGRAM
 
 void SceneViewer::paintGL() {
 #ifdef _DEBUG
@@ -2670,9 +2711,9 @@ void SceneViewer::fitToCamera() {
   TPointD P01       = cameraAff * cameraRect.getP01();
   TPointD P11       = cameraAff * cameraRect.getP11();
   TPointD p0        = TPointD(std::min({P00.x, P01.x, P10.x, P11.x}),
-                       std::min({P00.y, P01.y, P10.y, P11.y}));
+                              std::min({P00.y, P01.y, P10.y, P11.y}));
   TPointD p1        = TPointD(std::max({P00.x, P01.x, P10.x, P11.x}),
-                       std::max({P00.y, P01.y, P10.y, P11.y}));
+                              std::max({P00.y, P01.y, P10.y, P11.y}));
   cameraRect        = TRectD(p0.x, p0.y, p1.x, p1.y);
 
   // Pan
@@ -2715,9 +2756,9 @@ void SceneViewer::fitToCameraOutline() {
   TPointD P01       = cameraAff * cameraRect.getP01();
   TPointD P11       = cameraAff * cameraRect.getP11();
   TPointD p0        = TPointD(std::min({P00.x, P01.x, P10.x, P11.x}),
-                       std::min({P00.y, P01.y, P10.y, P11.y}));
+                              std::min({P00.y, P01.y, P10.y, P11.y}));
   TPointD p1        = TPointD(std::max({P00.x, P01.x, P10.x, P11.x}),
-                       std::max({P00.y, P01.y, P10.y, P11.y}));
+                              std::max({P00.y, P01.y, P10.y, P11.y}));
   cameraRect        = TRectD(p0.x, p0.y, p1.x, p1.y);
 
   // Pan
diff --git a/toonz/sources/toonz/subcameramanager.cpp b/toonz/sources/toonz/subcameramanager.cpp
index d3d941b..21d4852 100644
--- a/toonz/sources/toonz/subcameramanager.cpp
+++ b/toonz/sources/toonz/subcameramanager.cpp
@@ -31,6 +31,11 @@ inline bool bitwiseContains(UCHAR flag, UCHAR state) {
 inline bool bitwiseExclude(UCHAR flag, UCHAR state) {
   return bitwiseContains(~state, flag);
 }
+
+inline bool areNear(double v0, double v1, double thres = 20.0) {
+  return std::abs(v0 - v1) < thres;
+}
+
 }  // namespace
 
 //********************************************************************************
@@ -147,6 +152,27 @@ bool PreviewSubCameraManager::mouseMoveEvent(SceneViewer *viewer,
       TPointD worldCurPos(viewer->winToWorld(curPos));
 
       TApp *app = TApp::instance();
+
+      TCamera *camera = app->getCurrentScene()->getScene()->getCurrentCamera();
+      TRectD cameraStageRect(camera->getCameraToStageRef() *
+                             convert(TRect(camera->getRes())));
+
+      // Snap to the current camera frame
+      // horizontal
+      if (worldCurPos.x < worldMousePressPos.x &&
+          areNear(worldCurPos.x, cameraStageRect.x0))
+        worldCurPos.x = cameraStageRect.x0;
+      else if (worldCurPos.x > worldMousePressPos.x &&
+               areNear(worldCurPos.x, cameraStageRect.x1))
+        worldCurPos.x = cameraStageRect.x1;
+      // vertical
+      if (worldCurPos.y < worldMousePressPos.y &&
+          areNear(worldCurPos.y, cameraStageRect.y0))
+        worldCurPos.y = cameraStageRect.y0;
+      else if (worldCurPos.y > worldMousePressPos.y &&
+               areNear(worldCurPos.y, cameraStageRect.y1))
+        worldCurPos.y = cameraStageRect.y1;
+
       TAffine cameraAffInv(
           app->getCurrentXsheet()
               ->getXsheet()
@@ -162,15 +188,17 @@ bool PreviewSubCameraManager::mouseMoveEvent(SceneViewer *viewer,
           std::max(worldMousePressPos.x, worldCurPos.x),
           std::max(worldMousePressPos.y, worldCurPos.y));
 
-      TCamera *camera = app->getCurrentScene()->getScene()->getCurrentCamera();
       // camera->setInterestStageRect(worldPreviewSubCameraRect);
 
       TRectD previewSubCameraD(camera->getStageToCameraRef() *
                                worldPreviewSubCameraRect);
       m_editingInterestRect =
           TRect(previewSubCameraD.x0, previewSubCameraD.y0,
-                previewSubCameraD.x1 - 1, previewSubCameraD.y1 - 1) *
-          TRect(camera->getRes());
+                previewSubCameraD.x1 - 1, previewSubCameraD.y1 - 1);
+      // m_editingInterestRect =
+      //   TRect(previewSubCameraD.x0, previewSubCameraD.y0,
+      //     previewSubCameraD.x1 - 1, previewSubCameraD.y1 - 1) *
+      //   TRect(camera->getRes());
 
       viewer->update();
     } else {
@@ -194,7 +222,8 @@ bool PreviewSubCameraManager::mouseMoveEvent(SceneViewer *viewer,
           subRect.y1 = subRect.y1 + dragDistance.y;
       }
 
-      m_editingInterestRect = subRect * TRect(camera->getRes());
+      m_editingInterestRect = subRect;
+      // m_editingInterestRect = subRect * TRect(camera->getRes());
 
       viewer->update();
     }
@@ -301,11 +330,32 @@ UCHAR PreviewSubCameraManager::getSubCameraDragEnum(SceneViewer *viewer,
 
 //-----------------------------------------------------------------------------
 
-TPoint PreviewSubCameraManager::getSubCameraDragDistance(
-    SceneViewer *viewer, const QPointF &mousePos) {
+TPoint PreviewSubCameraManager::getSubCameraDragDistance(SceneViewer *viewer,
+                                                         QPointF &mousePos) {
   // Build the camera drag distance
   if (m_clickAndDrag) return TPoint();
 
+  // Snap to the current camera frame
+  TCamera *camera =
+      TApp::instance()->getCurrentScene()->getScene()->getCurrentCamera();
+  if (!bitwiseExclude(m_dragType, OUTER)) {
+    TPointD btmLft(cameraToWin(viewer, TPointD(0, 0)));
+    TPointD tpRght(
+        cameraToWin(viewer, TPointD(camera->getRes().lx, camera->getRes().ly)));
+    if (bitwiseContains(m_dragType, DRAG_LEFT) &&
+        areNear(mousePos.x(), btmLft.x))
+      mousePos.setX(btmLft.x);
+    else if (bitwiseContains(m_dragType, DRAG_RIGHT) &&
+             areNear(mousePos.x(), tpRght.x))
+      mousePos.setX(tpRght.x);
+    if (bitwiseContains(m_dragType, DRAG_BOTTOM) &&
+        areNear(mousePos.y(), (double)viewer->height() - btmLft.y))
+      mousePos.setY((double)viewer->height() - btmLft.y);
+    else if (bitwiseContains(m_dragType, DRAG_TOP) &&
+             areNear(mousePos.y(), (double)viewer->height() - tpRght.y))
+      mousePos.setY((double)viewer->height() - tpRght.y);
+  }
+
   TPointD cameraMousePos(winToCamera(viewer, mousePos));
 
   if (bitwiseExclude(m_dragType, OUTER)) {
@@ -313,8 +363,6 @@ TPoint PreviewSubCameraManager::getSubCameraDragDistance(
     return TPoint(resultD.x, resultD.y);
   }
 
-  TCamera *camera =
-      TApp::instance()->getCurrentScene()->getScene()->getCurrentCamera();
   TRect subCamera = camera->getInterestRect();
   TRectD subCameraD(subCamera.x0, subCamera.y0, subCamera.x1 + 1,
                     subCamera.y1 + 1);
diff --git a/toonz/sources/toonz/subcameramanager.h b/toonz/sources/toonz/subcameramanager.h
index 3f89a8c..778ce0c 100644
--- a/toonz/sources/toonz/subcameramanager.h
+++ b/toonz/sources/toonz/subcameramanager.h
@@ -110,7 +110,7 @@ private:
   TPointD cameraToWin(SceneViewer *viewer, const TPointD &cameraPos) const;
 
   UCHAR getSubCameraDragEnum(SceneViewer *viewer, const QPointF &mousePos);
-  TPoint getSubCameraDragDistance(SceneViewer *viewer, const QPointF &mousePos);
+  TPoint getSubCameraDragDistance(SceneViewer *viewer, QPointF &mousePos);
 };
 
 #endif  // SUBCAMERAMANAGER_INCLUDED
diff --git a/toonz/sources/toonz/viewerpane.cpp b/toonz/sources/toonz/viewerpane.cpp
index 6238d77..ef1a0bc 100644
--- a/toonz/sources/toonz/viewerpane.cpp
+++ b/toonz/sources/toonz/viewerpane.cpp
@@ -45,6 +45,8 @@
 #include "xsheetdragtool.h"
 #include "ruler.h"
 #include "menubarcommandids.h"
+#include "tenv.h"
+#include "cellselection.h"
 
 // Qt includes
 #include <QPainter>
@@ -67,6 +69,7 @@
 
 using namespace DVGui;
 
+extern TEnv::IntVar EnvViewerPreviewBehavior;
 //=============================================================================
 //
 // BaseViewerPanel
@@ -138,7 +141,7 @@ BaseViewerPanel::BaseViewerPanel(QWidget *parent, Qt::WindowFlags flags)
                      this, SLOT(onButtonPressed(FlipConsole::EGadget)));
 
   ret = ret && connect(m_sceneViewer, SIGNAL(previewStatusChanged()), this,
-                       SLOT(update()));
+                       SLOT(onPreviewStatusChanged()));
   ret = ret && connect(m_sceneViewer, SIGNAL(onFlipHChanged(bool)), this,
                        SLOT(setFlipHButtonChecked(bool)));
   ret = ret && connect(m_sceneViewer, SIGNAL(onFlipVChanged(bool)), this,
@@ -147,6 +150,9 @@ BaseViewerPanel::BaseViewerPanel(QWidget *parent, Qt::WindowFlags flags)
   ret = ret && connect(app->getCurrentScene(), SIGNAL(sceneSwitched()), this,
                        SLOT(onSceneSwitched()));
 
+  ret = ret && connect(app, SIGNAL(activeViewerChanged()), this,
+                       SLOT(onActiveViewerChanged()));
+
   assert(ret);
 
   setFocusProxy(m_sceneViewer);
@@ -256,7 +262,7 @@ void BaseViewerPanel::onDrawFrame(int frame,
   }
 
   // assert(frame >= 0); // frame can be negative in rare cases
-  if (frame != frameHandle->getFrameIndex() + 1) {
+  if (frame != frameHandle->getFrameIndex() + 1 && !settings.m_drawBlankFrame) {
     int oldFrame = frameHandle->getFrame();
     frameHandle->setCurrentFrame(frame);
     if (!frameHandle->isPlaying() && !frameHandle->isEditingLevel() &&
@@ -429,30 +435,51 @@ void BaseViewerPanel::initializeTitleBar(TPanelTitleBar *titleBar) {
                        SLOT(freeze(bool)));
 
   // preview toggles
-  m_previewButton = new TPanelTitleBarButton(
+  m_previewButton = new TPanelTitleBarButtonForPreview(
       titleBar, getIconThemePath("actions/20/pane_preview.svg"));
   x += 10 + iconWidth;
   titleBar->add(QPoint(x, 0), m_previewButton);
   m_previewButton->setToolTip(tr("Preview"));
-  ret = ret && connect(m_previewButton, SIGNAL(toggled(bool)),
-                       SLOT(enableFullPreview(bool)));
 
-  m_subcameraPreviewButton = new TPanelTitleBarButton(
+  // ret = ret && connect(m_previewButton, SIGNAL(toggled(bool)),
+  //                      SLOT(enableFullPreview(bool)));
+
+  m_subcameraPreviewButton = new TPanelTitleBarButtonForPreview(
       titleBar, getIconThemePath("actions/20/pane_subpreview.svg"));
   x += 1 + 24;  // width of pane_preview.svg = 24px
 
   titleBar->add(QPoint(x, 0), m_subcameraPreviewButton);
   m_subcameraPreviewButton->setToolTip(tr("Sub-camera Preview"));
-  ret = ret && connect(m_subcameraPreviewButton, SIGNAL(toggled(bool)),
-                       SLOT(enableSubCameraPreview(bool)));
+
+  // ret = ret && connect(m_subcameraPreviewButton, SIGNAL(toggled(bool)),
+  //                      SLOT(enableSubCameraPreview(bool)));
 
   assert(ret);
 }
 
 //-----------------------------------------------------------------------------
 
+void BaseViewerPanel::getPreviewButtonStates(bool &prev, bool &subCamPrev) {
+  prev       = m_previewButton->isChecked();
+  subCamPrev = m_subcameraPreviewButton->isChecked();
+}
+
+//-----------------------------------------------------------------------------
+
 void BaseViewerPanel::enableFullPreview(bool enabled) {
   m_subcameraPreviewButton->setPressed(false);
+  if (CommandManager::instance()
+          ->getAction(MI_ToggleViewerSubCameraPreview)
+          ->isChecked())
+    CommandManager::instance()
+        ->getAction(MI_ToggleViewerSubCameraPreview)
+        ->setChecked(false);
+
+  if (!enabled && EnvViewerPreviewBehavior == 2 &&
+      FlipConsole::getCurrent() == m_flipConsole &&
+      TApp::instance()->getCurrentFrame()->isPlaying())
+    CommandManager::instance()->execute(MI_Pause);
+
   m_sceneViewer->enablePreview(enabled ? SceneViewer::FULL_PREVIEW
                                        : SceneViewer::NO_PREVIEW);
   m_flipConsole->setProgressBarStatus(
@@ -464,6 +491,18 @@ void BaseViewerPanel::enableFullPreview(bool enabled) {
 
 void BaseViewerPanel::enableSubCameraPreview(bool enabled) {
   m_previewButton->setPressed(false);
+  if (CommandManager::instance()
+          ->getAction(MI_ToggleViewerPreview)
+          ->isChecked())
+    CommandManager::instance()
+        ->getAction(MI_ToggleViewerPreview)
+        ->setChecked(false);
+
+  if (!enabled && EnvViewerPreviewBehavior == 2 &&
+      FlipConsole::getCurrent() == m_flipConsole &&
+      TApp::instance()->getCurrentFrame()->isPlaying())
+    CommandManager::instance()->execute(MI_Pause);
+
   m_sceneViewer->enablePreview(enabled ? SceneViewer::SUBCAMERA_PREVIEW
                                        : SceneViewer::NO_PREVIEW);
   m_flipConsole->setProgressBarStatus(
@@ -509,6 +548,26 @@ void BaseViewerPanel::onPlayingStatusChanged(bool playing) {
     m_playing = false;
     m_first   = true;
   }
+
+  // if preview behavior mode is "selected cells", release preview mode when
+  // stopped
+  if (!playing && EnvViewerPreviewBehavior == 2 &&
+      FlipConsole::getCurrent() == m_flipConsole &&
+      !Previewer::instance(m_sceneViewer->getPreviewMode() ==
+                           SceneViewer::SUBCAMERA_PREVIEW)
+           ->isBusy()) {
+    if (CommandManager::instance()
+            ->getAction(MI_ToggleViewerPreview)
+            ->isChecked())
+      CommandManager::instance()->getAction(MI_ToggleViewerPreview)->trigger();
+    else if (CommandManager::instance()
+                 ->getAction(MI_ToggleViewerSubCameraPreview)
+                 ->isChecked())
+      CommandManager::instance()
+          ->getAction(MI_ToggleViewerSubCameraPreview)
+          ->trigger();
+  }
+
   if (Preferences::instance()->getOnionSkinDuringPlayback()) return;
   OnionSkinMask osm =
       TApp::instance()->getCurrentOnionSkin()->getOnionSkinMask();
@@ -800,6 +859,90 @@ void BaseViewerPanel::load(QSettings &settings) {
   updateShowHide();
 }
 
+//-----------------------------------------------------------------------------
+
+void BaseViewerPanel::onPreviewStatusChanged() {
+  // if preview behavior mode is "selected cells", play once the all frames are
+  // completed
+  if (EnvViewerPreviewBehavior == 2 &&
+      FlipConsole::getCurrent() == m_flipConsole &&
+      !TApp::instance()->getCurrentFrame()->isPlaying() &&
+      m_sceneViewer->isPreviewEnabled() &&
+      !Previewer::instance(m_sceneViewer->getPreviewMode() ==
+                           SceneViewer::SUBCAMERA_PREVIEW)
+           ->isBusy()) {
+    TCellSelection *cellSel =
+        dynamic_cast<TCellSelection *>(TSelection::getCurrent());
+    if (cellSel && !cellSel->isEmpty()) {
+      int r0, c0, r1, c1;
+      cellSel->getSelectedCells(r0, c0, r1, c1);
+      if (r0 < r1) {
+        // check if all frame range is rendered. this check is needed since
+        // isBusy() will not be true just after the preview is triggered
+        for (int r = r0; r <= r1; r++) {
+          if (!Previewer::instance(m_sceneViewer->getPreviewMode() ==
+                                   SceneViewer::SUBCAMERA_PREVIEW)
+                   ->isFrameReady(r)) {
+            update();
+            return;
+          }
+        }
+        m_flipConsole->setStopAt(r1 + 1);
+        m_flipConsole->setStartAt(r0 + 1);
+        TApp::instance()->getCurrentFrame()->setFrame(r0);
+        CommandManager::instance()->execute(MI_Loop);
+      }
+    }
+  }
+
+  update();
+}
+
+//-----------------------------------------------------------------------------
+// sync preview commands and buttons states when the viewer becomes active
+
+void BaseViewerPanel::onActiveViewerChanged() {
+  bool ret = true;
+  if (TApp::instance()->getActiveViewer() == m_sceneViewer) {
+    ret = ret &&
+          connect(m_previewButton, SIGNAL(toggled(bool)),
+                  CommandManager::instance()->getAction(MI_ToggleViewerPreview),
+                  SLOT(trigger()));
+    ret = ret &&
+          connect(CommandManager::instance()->getAction(MI_ToggleViewerPreview),
+                  SIGNAL(triggered(bool)), m_previewButton,
+                  SLOT(setPressed(bool)));
+    ret        = ret && connect(m_subcameraPreviewButton, SIGNAL(toggled(bool)),
+                                CommandManager::instance()->getAction(
+                             MI_ToggleViewerSubCameraPreview),
+                                SLOT(trigger()));
+    ret        = ret && connect(CommandManager::instance()->getAction(
+                             MI_ToggleViewerSubCameraPreview),
+                                SIGNAL(triggered(bool)), m_subcameraPreviewButton,
+                                SLOT(setPressed(bool)));
+    m_isActive = true;
+  } else if (m_isActive) {
+    ret = ret && disconnect(m_previewButton, SIGNAL(toggled(bool)),
+                            CommandManager::instance()->getAction(
+                                MI_ToggleViewerPreview),
+                            SLOT(trigger()));
+    ret = ret &&
+          disconnect(
+              CommandManager::instance()->getAction(MI_ToggleViewerPreview),
+              SIGNAL(triggered(bool)), m_previewButton, SLOT(setPressed(bool)));
+    ret = ret && disconnect(m_subcameraPreviewButton, SIGNAL(toggled(bool)),
+                            CommandManager::instance()->getAction(
+                                MI_ToggleViewerSubCameraPreview),
+                            SLOT(trigger()));
+    ret = ret && disconnect(CommandManager::instance()->getAction(
+                                MI_ToggleViewerSubCameraPreview),
+                            SIGNAL(triggered(bool)), m_subcameraPreviewButton,
+                            SLOT(setPressed(bool)));
+    m_isActive = false;
+  }
+  assert(ret);
+}
+
 //=============================================================================
 //
 // SceneViewerPanel
@@ -842,4 +985,45 @@ void SceneViewerPanel::checkOldVersionVisblePartsFlags(QSettings &settings) {
       settings.value("visibleParts", m_visiblePartsFlag).toUInt();
   settings.remove("visibleParts");
   settings.setValue("viewerVisibleParts", m_visiblePartsFlag);
-}
\ No newline at end of file
+}
+
+//=========================================================
+
+class ViewerPreviewCommands : public QObject {
+public:
+  ViewerPreviewCommands() {
+    setCommandHandler("MI_ToggleViewerPreview", this,
+                      &ViewerPreviewCommands::onPreview);
+    setCommandHandler("MI_ToggleViewerSubCameraPreview", this,
+                      &ViewerPreviewCommands::onSubCameraPreview);
+  }
+
+  void onPreview();
+  void onSubCameraPreview();
+};
+
+void ViewerPreviewCommands::onPreview() {
+  SceneViewer *activeViewer = TApp::instance()->getActiveViewer();
+  if (!activeViewer) return;
+  BaseViewerPanel *bvp = qobject_cast<BaseViewerPanel *>(
+      activeViewer->parentWidget()->parentWidget());
+  if (!bvp) return;
+  bool on = CommandManager::instance()
+                ->getAction(MI_ToggleViewerPreview)
+                ->isChecked();
+  bvp->enableFullPreview(on);
+}
+
+void ViewerPreviewCommands::onSubCameraPreview() {
+  SceneViewer *activeViewer = TApp::instance()->getActiveViewer();
+  if (!activeViewer) return;
+  BaseViewerPanel *bvp = qobject_cast<BaseViewerPanel *>(
+      activeViewer->parentWidget()->parentWidget());
+  if (!bvp) return;
+  bool on = CommandManager::instance()
+                ->getAction(MI_ToggleViewerSubCameraPreview)
+                ->isChecked();
+  bvp->enableSubCameraPreview(on);
+}
+
+ViewerPreviewCommands viewerPreviewCommands;
diff --git a/toonz/sources/toonz/viewerpane.h b/toonz/sources/toonz/viewerpane.h
index 6ec8889..953a7dd 100644
--- a/toonz/sources/toonz/viewerpane.h
+++ b/toonz/sources/toonz/viewerpane.h
@@ -52,8 +52,8 @@ protected:
   FlipConsole *m_flipConsole;
   ViewerKeyframeNavigator *m_keyFrameButton;
   TPanelTitleBarButtonSet *m_referenceModeBs;
-  TPanelTitleBarButton *m_previewButton;
-  TPanelTitleBarButton *m_subcameraPreviewButton;
+  TPanelTitleBarButtonForPreview *m_previewButton;
+  TPanelTitleBarButtonForPreview *m_subcameraPreviewButton;
   bool m_onionSkinActive = false;
   UINT m_visiblePartsFlag;
   bool m_playSound     = true;
@@ -65,6 +65,8 @@ protected:
   bool m_first         = true;
   TSoundTrack *m_sound = NULL;
 
+  bool m_isActive = false;
+
 public:
   BaseViewerPanel(QWidget *parent = 0, Qt::WindowFlags flags = 0);
   ~BaseViewerPanel() {}
@@ -91,6 +93,8 @@ public:
 
   void initializeTitleBar(TPanelTitleBar *titleBar);
 
+  void getPreviewButtonStates(bool &prev, bool &subCamPrev);
+
 protected:
   void contextMenuEvent(QContextMenuEvent *event) override;
   void showEvent(QShowEvent *) override;
@@ -111,6 +115,8 @@ public slots:
   void onButtonPressed(FlipConsole::EGadget button);
   void setFlipHButtonChecked(bool checked);
   void setFlipVButtonChecked(bool checked);
+  void enableFullPreview(bool enabled);
+  void enableSubCameraPreview(bool enabled);
 
 protected slots:
 
@@ -120,8 +126,8 @@ protected slots:
   void onPlayingStatusChanged(bool playing);
   // for showing/hiding the parts
   void onShowHideActionTriggered(QAction *);
-  void enableFullPreview(bool enabled);
-  void enableSubCameraPreview(bool enabled);
+  void onPreviewStatusChanged();
+  void onActiveViewerChanged();
 };
 
 class SceneViewerPanel final : public BaseViewerPanel {
diff --git a/toonz/sources/toonzlib/tcamera.cpp b/toonz/sources/toonzlib/tcamera.cpp
index 99d68c9..5710c5d 100644
--- a/toonz/sources/toonzlib/tcamera.cpp
+++ b/toonz/sources/toonzlib/tcamera.cpp
@@ -11,9 +11,7 @@
 TCamera::TCamera()
     //: m_size(12, 9), m_res(768, 576), m_xPrevalence(true)
     //: m_size(36, 20.25),
-    : m_size(16, 9),
-      m_res(1920, 1080),
-      m_xPrevalence(true) {}
+    : m_size(16, 9), m_res(1920, 1080), m_xPrevalence(true) {}
 
 //-------------------------------------------------------------------
 
@@ -110,15 +108,18 @@ TRectD TCamera::getStageRect() const {
 //-------------------------------------------------------------------
 
 void TCamera::setInterestRect(const TRect &rect) {
-  // Not using the TRect's common intersection. Unfortunately, in case
-  // the rect's coordinates have lx or ly < 0, the intersection returns
-  // the default (empty) rect. We want to maintain the coordinates instead.
-  // m_interestRect = rect * TRect(m_res);
-
-  m_interestRect.x0 = std::max(rect.x0, 0);
-  m_interestRect.y0 = std::max(rect.y0, 0);
-  m_interestRect.x1 = std::min(rect.x1, m_res.lx - 1);
-  m_interestRect.y1 = std::min(rect.y1, m_res.ly - 1);
+  // enable to preview outside of the original camera rect
+  m_interestRect = rect;
+  return;
+  //// Not using the TRect's common intersection. Unfortunately, in case
+  //// the rect's coordinates have lx or ly < 0, the intersection returns
+  //// the default (empty) rect. We want to maintain the coordinates instead.
+  //// m_interestRect = rect * TRect(m_res);
+  //
+  // m_interestRect.x0 = std::max(rect.x0, 0);
+  // m_interestRect.y0 = std::max(rect.y0, 0);
+  // m_interestRect.x1 = std::min(rect.x1, m_res.lx - 1);
+  // m_interestRect.y1 = std::min(rect.y1, m_res.ly - 1);
 }
 
 //-------------------------------------------------------------------
diff --git a/toonz/sources/toonzqt/flipconsole.cpp b/toonz/sources/toonzqt/flipconsole.cpp
index 5f52a7f..8972b81 100644
--- a/toonz/sources/toonzqt/flipconsole.cpp
+++ b/toonz/sources/toonzqt/flipconsole.cpp
@@ -830,9 +830,11 @@ void FlipConsole::onNextFrame(int fps, QElapsedTimer *timer,
     else
       m_fpsField->setLineEditBackgroundColor(Qt::red);
   }
-  if (m_stopAt > 0 && m_currentFrame >= m_stopAt) {
+  if (m_stopAt > 0 && m_currentFrame >= m_stopAt &&
+      (m_isPlay || m_startAt == -1)) {
     doButtonPressed(ePause);
-    m_stopAt = -1;
+    m_stopAt  = -1;
+    m_startAt = -1;
   }
 }
 
@@ -842,6 +844,10 @@ void FlipConsole::playNextFrame(QElapsedTimer *timer, qint64 targetInstant) {
   int from = m_from, to = m_to;
   if (m_markerFrom <= m_markerTo && m_stopAt == -1)
     from = m_markerFrom, to = m_markerTo;
+  else if (m_stopAt > 0 && m_startAt > 0) {
+    from = m_startAt;
+    to   = m_stopAt;
+  }
 
   if (m_framesCount == 0 ||
       (m_isPlay && m_currentFrame == (m_reverse ? from : to))) {
@@ -1506,6 +1512,7 @@ void FlipConsole::onButtonPressed(int button) {
           playingConsole->setChecked(ePause, true);
           stoppedOther = true;
           m_stopAt     = -1;
+          m_startAt    = -1;
         }
       }
       if (stoppedOther) {
@@ -1656,7 +1663,8 @@ void FlipConsole::doButtonPressed(UINT button) {
           playingConsole->setChecked(ePause, true);
         }
       }
-      m_stopAt = -1;
+      m_stopAt  = -1;
+      m_startAt = -1;
       return;
     }
 
@@ -1665,6 +1673,7 @@ void FlipConsole::doButtonPressed(UINT button) {
     if (m_playbackExecutor.isRunning()) m_playbackExecutor.abort();
 
     m_stopAt       = -1;
+    m_startAt      = -1;
     m_isPlay       = false;
     m_blanksToDraw = 0;
 
@@ -1808,6 +1817,10 @@ void FlipConsole::setStopAt(int frame) { m_stopAt = frame; }
 
 //--------------------------------------------------------------------
 
+void FlipConsole::setStartAt(int frame) { m_startAt = frame; }
+
+//--------------------------------------------------------------------
+
 QFrame *FlipConsole::createFrameSlider() {
   QFrame *frameSliderFrame = new QFrame(this);