+Timeline::mouse_wheel_turned(wxMouseEvent& event)
+{
+ auto const rotation = event.GetWheelRotation();
+
+ if (event.ControlDown()) {
+ /* On my mouse one click of the scroll wheel is 120, and it's -ve when
+ * scrolling the wheel towards me.
+ */
+ auto const scale = rotation > 0 ?
+ (1.0 / (rotation / 90.0)) :
+ (-rotation / 90.0);
+
+ int before_start_x;
+ int before_start_y;
+ _main_canvas->GetViewStart(&before_start_x, &before_start_y);
+
+ auto const before_pps = _pixels_per_second.get_value_or(1);
+ auto const before_pos = _last_mouse_wheel_x && *_last_mouse_wheel_x == event.GetX() ?
+ *_last_mouse_wheel_time :
+ (before_start_x * _x_scroll_rate + event.GetX()) / before_pps;
+
+ set_pixels_per_second(before_pps * scale);
+ setup_scrollbars();
+
+ auto after_left = std::max(0.0, before_pos * _pixels_per_second.get_value_or(1) - event.GetX());
+ _main_canvas->Scroll(after_left / _x_scroll_rate, before_start_y);
+ _labels_canvas->Scroll(0, before_start_y);
+ Refresh();
+
+ if (!_last_mouse_wheel_x || *_last_mouse_wheel_x != event.GetX()) {
+ _last_mouse_wheel_x = event.GetX();
+ _last_mouse_wheel_time = before_pos;
+ }
+ } else if (event.ShiftDown()) {
+ int before_start_x;
+ int before_start_y;
+ _main_canvas->GetViewStart(&before_start_x, &before_start_y);
+ auto const width = _main_canvas->GetSize().GetWidth();
+ _main_canvas->Scroll(std::max(0.0, before_start_x - rotation * 100.0 / width), before_start_y);
+ }
+}
+
+
+void
+Timeline::update_playhead ()