Implement drag-scrub, compatibly with the existing move-scrub...

... Start scrub by click or double click on the scrub head; release button or
not; then move.

If you release before moving, you get scrubbing as before, controlled by
motion.  Click or drag to switch in and out of seeking.  Stop with ESC,
spacebar, etc.  No change of selection.

But now if you drag, then scrubbing contines until you release the mouse or
otherwise stop with a key.

If by release of the mouse, then the selection changes as if by a click at
the last play position.  If you hold shift, then, as if by shift-click.

If drag begins with a double-click, then the play head remains centered and
the track moves.

src/tracks/ui/Scrubbing.cpp

@@ -230,6 +230,9 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
    if (IsScrubbing())
       return false;
    else {
+      const auto state = ::wxGetMouseState();
+      mDragging = state.LeftIsDown();
+
       const bool busy = gAudioIO->IsBusy();
       if (busy && gAudioIO->GetNumCaptureChannels() > 0) {
          // Do not stop recording, and don't try to start scrubbing after
@@ -259,6 +262,14 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
                mScrubStartPosition = position;
             }
 
+            if (mDragging && mSmoothScrollingScrub) {
+               auto delta = time0 - time1;
+               time0 = std::max(0.0, std::min(maxTime,
+                  (viewInfo.h + mProject->GetScreenEndTime()) / 2
+               ));
+               time1 = time0 + delta;
+            }
+
             AudioIOStartStreamOptions options(mProject->GetDefaultPlayOptions());
             options.timeTrack = NULL;
             options.scrubDelay = (kTimerInterval / 1000.0);
@@ -272,8 +283,10 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
                p->GetTranscriptionToolBar()->GetPlaySpeed();
             }
 #else
-            // That idea seems unpopular... just make it one
-            mMaxScrubSpeed = options.maxScrubSpeed = 1.0;
+            // That idea seems unpopular... just make it one for move-scrub,
+            // but big for drag-scrub
+            mMaxScrubSpeed = options.maxScrubSpeed =
+               mDragging ? AudioIO::GetMaxScrubSpeed() : 1.0;
 #endif
             options.maxScrubTime = mProject->GetTracks()->GetEndTime();
             ControlToolBar::PlayAppearance appearance =
@@ -300,6 +313,7 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
       if (IsScrubbing()) {
          mProject->GetPlaybackScroller().Activate(mSmoothScrollingScrub);
          mScrubHasFocus = true;
+         mLastScrubPosition = xx;
       }
 
       // Return true whether we started scrub, or are still waiting to decide.
@@ -309,13 +323,19 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
 
 void Scrubber::ContinueScrubbing()
 {
+   const wxMouseState state(::wxGetMouseState());
+
+   if (mDragging && !state.LeftIsDown()) {
+      // Stop and set cursor
+      mProject->DoPlayStopSelect(true, state.ShiftDown());
+      return;
+   }
 
    // Thus scrubbing relies mostly on periodic polling of mouse and keys,
    // not event notifications.  But there are a few event handlers that
    // leave messages for this routine, in mScrubSeekPress and in mScrubHasFocus.
 
    // Seek only when the pointer is in the panel.  Else, scrub.
-   const wxMouseState state(::wxGetMouseState());
    TrackPanel *const trackPanel = mProject->GetTrackPanel();
 
    // Decide whether to skip play, because either mouse is down now,
@@ -333,13 +353,21 @@ void Scrubber::ContinueScrubbing()
    }
 
    const wxPoint position = trackPanel->ScreenToClient(state.GetPosition());
-   // When we don't have focus, enqueue silent scrubs until we regain focus.
+   const auto &viewInfo = mProject->GetViewInfo();
+
    bool result = false;
    if (!mScrubHasFocus)
+      // When we don't have focus, enqueue silent scrubs until we regain focus.
       result = gAudioIO->EnqueueScrubBySignedSpeed(0, mMaxScrubSpeed, false);
+   else if (mDragging && mSmoothScrollingScrub) {
+      const auto lastTime = gAudioIO->GetLastTimeInScrubQueue();
+      const auto delta = mLastScrubPosition - position.x;
+      const double time = viewInfo.OffsetTimeByPixels(lastTime, delta);
+      result = gAudioIO->EnqueueScrubByPosition(time, mMaxScrubSpeed, false);
+      mLastScrubPosition = position.x;
+   }
    else {
-      const double time = mProject->GetViewInfo().PositionToTime(position.x, trackPanel->GetLeftOffset());
-
+      const double time = viewInfo.PositionToTime(position.x, trackPanel->GetLeftOffset());
       if (seek)
          // Cause OnTimer() to suppress the speed display
          mScrubSpeedDisplayCountdown = 1;
@@ -372,6 +400,7 @@ void Scrubber::StopScrubbing()
 
    mScrubStartPosition = -1;
    mProject->GetPlaybackScroller().Activate(false);
+   mDragging = false;
 
    if (!IsScrubbing())
    {
@@ -382,6 +411,11 @@ void Scrubber::StopScrubbing()
    }
 
    mProject->GetRulerPanel()->HideQuickPlayIndicator();
+
+   // Need this in case ruler gets the mouse-up event after escaping scrubbing:
+   // prevent reappearance of the
+   // quick play guideline
+   mProject->GetRulerPanel()->IgnoreMouseUp();
 }
 
 bool Scrubber::IsScrubbing() const
@@ -400,6 +434,9 @@ bool Scrubber::IsScrubbing() const
 
 bool Scrubber::ShouldDrawScrubSpeed()
 {
+   if (mDragging)
+      return false;
+
    return IsScrubbing() &&
       mScrubHasFocus && (
       // Draw for (non-scroll) scrub, sometimes, but never for seek
@@ -419,6 +456,10 @@ double Scrubber::FindScrubSpeed(bool seeking, double time) const
 
 void Scrubber::HandleScrollWheel(int steps)
 {
+   if (mDragging)
+      // Not likely you would spin it with the left button down, but...
+      return;
+
    const int newLogMaxScrubSpeed = mLogMaxScrubSpeed + steps;
    static const double maxScrubSpeedBase =
       pow(2.0, 1.0 / ScrubSpeedStepsPerOctave);
@@ -450,7 +491,8 @@ void Scrubber::Forwarder::OnMouse(wxMouseEvent &event)
    if (isScrubbing && !event.HasAnyModifiers()) {
       if(event.LeftDown() ||
          (event.LeftIsDown() && event.Dragging())) {
-         scrubber.mScrubSeekPress = true;
+         if (!scrubber.mDragging)
+            scrubber.mScrubSeekPress = true;
          auto xx = ruler->ScreenToClient(::wxGetMousePosition()).x;
          ruler->UpdateQuickPlayPos(xx);
          ruler->ShowQuickPlayIndicator();
@@ -541,12 +583,13 @@ void ScrubbingOverlay::OnTimer(wxCommandEvent &event)
    auto position = ::wxGetMousePosition();
 
    {
-      auto xx = ruler->ScreenToClient(position).x;
-      ruler->UpdateQuickPlayPos(xx);
+      if(scrubber.HasStartedScrubbing()) {
+         auto xx = ruler->ScreenToClient(position).x;
+         ruler->UpdateQuickPlayPos(xx);
 
-      if(!isScrubbing && scrubber.HasStartedScrubbing()) {
-         // Really start scrub if motion is far enough
-         scrubber.MaybeStartScrubbing(xx);
+         if (!isScrubbing)
+            // Really start scrub if motion is far enough
+            scrubber.MaybeStartScrubbing(xx);
       }
 
       if (!isScrubbing) {
@@ -627,7 +670,7 @@ Scrubber &ScrubbingOverlay::GetScrubber()
 
 bool Scrubber::PollIsSeeking()
 {
-   return mAlwaysSeeking || ::wxGetMouseState().LeftIsDown();
+   return !mDragging && (mAlwaysSeeking || ::wxGetMouseState().LeftIsDown());
 }
 
 void Scrubber::DoScrub(bool scroll, bool seek)

src/tracks/ui/Scrubbing.h

@@ -109,10 +109,12 @@ private:
    bool mScrubHasFocus;
    int mScrubSpeedDisplayCountdown;
    wxCoord mScrubStartPosition;
+   wxCoord mLastScrubPosition {};
    double mMaxScrubSpeed;
    bool mScrubSeekPress;
    bool mSmoothScrollingScrub;
-   bool mAlwaysSeeking{};
+   bool mAlwaysSeeking {};
+   bool mDragging {};
 
 #ifdef EXPERIMENTAL_SCRUBBING_SCROLL_WHEEL
    int mLogMaxScrubSpeed;