Maintain active layer track in view

app/src/timeline.cpp

@@ -27,6 +27,7 @@ GNU General Public License for more details.
 #include <QLabel>
 #include <QWheelEvent>
 #include <QSlider>
+#include <QTimer>
 
 #include "editor.h"
 #include "layermanager.h"
@@ -191,12 +192,17 @@ void TimeLine::initUI()
     timeLineContent->setLayout(lay);
     setWidget(timeLineContent);
 
+    mScrollingStoppedTimer = new QTimer();
+    mScrollingStoppedTimer->setSingleShot(true);
+
     setWindowFlags(Qt::WindowStaysOnTopHint);
 
     connect(mHScrollbar, &QScrollBar::valueChanged, mTracks, &TimeLineCells::hScrollChange);
     connect(mTracks, &TimeLineCells::offsetChanged, mHScrollbar, &QScrollBar::setValue);
     connect(mVScrollbar, &QScrollBar::valueChanged, mTracks, &TimeLineCells::vScrollChange);
     connect(mVScrollbar, &QScrollBar::valueChanged, mLayerList, &TimeLineCells::vScrollChange);
+    connect(mVScrollbar, &QScrollBar::valueChanged, this, &TimeLine::onScrollbarValueChanged);
+    connect(mScrollingStoppedTimer, &QTimer::timeout, mLayerList, &TimeLineCells::onScrollingVerticallyStopped);
 
     connect(splitter, &QSplitter::splitterMoved, this, &TimeLine::updateLength);
 
@@ -232,7 +238,7 @@ void TimeLine::initUI()
 
     LayerManager* layer = editor()->layers();
     connect(layer, &LayerManager::layerCountChanged, this, &TimeLine::updateLayerNumber);
-    connect(layer, &LayerManager::currentLayerChanged, this, &TimeLine::onLayerChanged);
+    connect(layer, &LayerManager::currentLayerChanged, this, &TimeLine::onCurrentLayerChanged);
     mNumLayers = layer->count();
 
     scrubbing = false;
@@ -285,6 +291,12 @@ void TimeLine::wheelEvent(QWheelEvent* event)
     }
 }
 
+void TimeLine::onScrollbarValueChanged()
+{
+    // After the scrollbar has been updated, prepare to trigger stopped event
+    mScrollingStoppedTimer->start(150);
+}
+
 void TimeLine::updateFrame(int frameNumber)
 {
     Q_ASSERT(mTracks);
@@ -358,7 +370,27 @@ void TimeLine::onObjectLoaded()
     updateLayerNumber(editor()->layers()->count());
 }
 
-void TimeLine::onLayerChanged()
+void TimeLine::onCurrentLayerChanged()
 {
+    updateVerticalScrollbarPosition();
     mLayerDeleteButton->setEnabled(editor()->layers()->canDeleteLayer(editor()->currentLayerIndex()));
 }
+
+void TimeLine::updateVerticalScrollbarPosition()
+{
+    // invert index so 0 is at the top
+    int idx = mNumLayers - editor()->currentLayerIndex() - 1;
+    // number of visible layers
+    int height = mNumLayers - mVScrollbar->maximum();
+    // scroll bar position/offset
+    int pos = mVScrollbar->value();
+
+    if (idx < pos) // above visible area
+    {
+        mVScrollbar->setValue(idx);
+    }
+    else if (idx >= pos + height) // below visible area
+    {
+        mVScrollbar->setValue(idx - height + 1);
+    }
+}

app/src/timeline.h

@@ -25,6 +25,7 @@ class TimeLineCells;
 class TimeControls;
 
 class QToolButton;
+class QWheelEvent;
 
 
 class TimeLine : public BaseDockWidget
@@ -53,7 +54,8 @@ class TimeLine : public BaseDockWidget
     int getRangeUpper();
 
     void onObjectLoaded();
-    void onLayerChanged();
+    void onCurrentLayerChanged();
+    void onScrollbarValueChanged();
 
 signals:
     void selectionChanged();
@@ -76,6 +78,7 @@ class TimeLine : public BaseDockWidget
     void onionPrevClick();
     void onionNextClick();
     void playButtonTriggered();
+
 public:
     bool scrubbing = false;
 
@@ -84,12 +87,16 @@ class TimeLine : public BaseDockWidget
     void wheelEvent( QWheelEvent* ) override;
 
 private:
+    void updateVerticalScrollbarPosition();
+
     QScrollBar* mHScrollbar = nullptr;
     QScrollBar* mVScrollbar = nullptr;
     TimeLineCells* mTracks = nullptr;
     TimeLineCells* mLayerList = nullptr;
     TimeControls* mTimeControls = nullptr;
 
+    QTimer* mScrollingStoppedTimer = nullptr;
+
     QToolButton* mLayerDeleteButton = nullptr;
     int mNumLayers = 0;
     int mLastUpdatedFrame = 0;

app/src/timelinecells.cpp

@@ -1083,7 +1083,7 @@ void TimeLineCells::mouseReleaseEvent(QMouseEvent* event)
             updateContent();
         }
     }
-    if (mType == TIMELINE_CELL_TYPE::Layers && layerNumber != mStartLayerNumber && mStartLayerNumber != -1 && layerNumber != -1)
+    if (mType == TIMELINE_CELL_TYPE::Layers && !mScrollingVertically && layerNumber != mStartLayerNumber && mStartLayerNumber != -1 && layerNumber != -1)
     {
         mToLayer = getInbetweenLayerNumber(event->pos().y());
         if (mToLayer != mFromLayer && mToLayer > -1 && mToLayer < mEditor->layers()->count())
@@ -1210,9 +1210,15 @@ void TimeLineCells::hScrollChange(int x)
 void TimeLineCells::vScrollChange(int x)
 {
     mLayerOffset = x;
+    mScrollingVertically = true;
     updateContent();
 }
 
+void TimeLineCells::onScrollingVerticallyStopped()
+{
+    mScrollingVertically = false;
+}
+
 void TimeLineCells::setMouseMoveY(int x)
 {
     mMouseMoveY = x;

app/src/timelinecells.h

@@ -75,6 +75,7 @@ public slots:
     void updateFrame(int frameNumber);
     void hScrollChange(int);
     void vScrollChange(int);
+    void onScrollingVerticallyStopped();
     void setMouseMoveY(int x);
 
 protected:
@@ -152,6 +153,8 @@ private slots:
     int mLayerOffset = 0;
     Qt::MouseButton primaryButton = Qt::NoButton;
 
+    bool mScrollingVertically = false;
+
     bool mCanMoveFrame   = false;
     bool mMovingFrames   = false;