resizablescrollbar: refined timeline scrollbar resizing to be more accurate

app/widget/resizablescrollbar/resizablescrollbar.cpp

@@ -39,11 +39,8 @@ void ResizableScrollBar::mouseMoveEvent(QMouseEvent *event)
 
   QRect sr = style()->subControlRect(QStyle::CC_ScrollBar, &opt,
                                      QStyle::SC_ScrollBarSlider, this);
-  QRect gr = style()->subControlRect(QStyle::CC_ScrollBar, &opt,
-                                     QStyle::SC_ScrollBarGroove, this);
 
   if (mouse_dragging_) {
-
     int new_drag_pos = GetActiveMousePos(event);
     int mouse_movement = new_drag_pos - mouse_drag_start_;
     mouse_drag_start_ = new_drag_pos;
@@ -52,21 +49,29 @@ void ResizableScrollBar::mouseMoveEvent(QMouseEvent *event)
       mouse_movement = -mouse_movement;
     }
 
-    double scale_multiplier = static_cast<double>(sr.width()) / static_cast<double>(sr.width() + mouse_movement);
-    emit RequestScale(scale_multiplier);
+    double width_adjustment = static_cast<double>(sr.width() + mouse_movement);
 
-    if (mouse_handle_state_ == kInTopHandle) {
-      int slider_min = gr.x();
-      int slider_max = gr.right() - (sr.width() + mouse_movement);
-      int val = QStyle::sliderValueFromPosition(minimum(),
-                                                maximum(),
-                                                event->pos().x() - slider_min,
-                                                slider_max - slider_min,
-                                                opt.upsideDown);
+    // Prevent dividing by zero or emitting a negative scale
+    if (width_adjustment > 0) {
+      double scale_multiplier = static_cast<double>(sr.width()) / width_adjustment;
+      emit RequestScale(scale_multiplier);
 
-      setValue(val);
-    } else {
-      setValue(qRound(static_cast<double>(value()) * scale_multiplier));
+      if (mouse_handle_state_ == kInTopHandle) {
+        QRect gr = style()->subControlRect(QStyle::CC_ScrollBar, &opt,
+                                           QStyle::SC_ScrollBarGroove, this);
+
+        int slider_min = gr.x();
+        int slider_max = gr.right() - (sr.width() + mouse_movement);
+        int val = QStyle::sliderValueFromPosition(minimum(),
+                                                  maximum(),
+                                                  event->pos().x() - slider_min,
+                                                  slider_max - slider_min,
+                                                  opt.upsideDown);
+
+        setValue(val);
+      } else {
+        setValue(qRound(static_cast<double>(value()) * scale_multiplier));
+      }
     }
 
   } else {

app/widget/timebased/timebased.cpp

@@ -81,7 +81,22 @@ void TimeBasedWidget::UpdateMaximumScroll()
 
 void TimeBasedWidget::ScrollBarResized(const double &multiplier)
 {
-  SetScale(GetScale() * multiplier);
+  QScrollBar* bar = static_cast<QScrollBar*>(sender());
+
+  int current_max = bar->maximum();
+  double proposed_max = static_cast<double>(current_max) * multiplier;
+
+  proposed_max = proposed_max - (bar->width() * 0.5 / multiplier) + (bar->width() * 0.5);
+
+  double corrected_scale;
+
+  if (current_max == 0) {
+    corrected_scale = multiplier;
+  } else {
+    corrected_scale = (proposed_max / static_cast<double>(current_max));
+  }
+
+  SetScale(GetScale() * corrected_scale);
 }
 
 TimeRuler *TimeBasedWidget::ruler() const
@@ -146,6 +161,7 @@ void TimeBasedWidget::SetTimebase(const rational &timebase)
 
 void TimeBasedWidget::SetScale(const double &scale)
 {
+  // Simple QObject slot wrapper around TimelineScaledObject::SetScale()
   TimelineScaledObject::SetScale(scale);
 }
 

app/widget/timelinewidget/timelinescaledobject.cpp

@@ -71,7 +71,9 @@ const double& TimelineScaledObject::GetScale() const
 
 void TimelineScaledObject::SetScale(const double& scale)
 {
-  scale_ = scale;
+  Q_ASSERT(scale > 0);
+
+  scale_ = qMin(scale, max_scale_);
 
   ScaleChangedEvent(scale_);
 }