Bug 986 and other changes for more consistent zoom all and zoom fit...

... when there is audio before time zero.

src/Menus.cpp

@@ -4986,7 +4986,11 @@ void AudacityProject::OnZoomNormal()
 
 void AudacityProject::OnZoomFit()
 {
-   double len = mTracks->GetEndTime();
+   const double end = mTracks->GetEndTime();
+   const double start = mScrollBeyondZero
+      ? std::min(mTracks->GetStartTime(), 0.0)
+      : 0;
+   const double len = end - start;
 
    if (len <= 0.0)
       return;
@@ -4996,7 +5000,7 @@ void AudacityProject::OnZoomFit()
    w -= 10;
 
    Zoom(w / len);
-   TP_ScrollWindow(0.0);
+   TP_ScrollWindow(start);
 }
 
 void AudacityProject::DoZoomFitV()
@@ -5049,7 +5053,11 @@ void AudacityProject::OnZoomFitV()
 
 void AudacityProject::OnZoomSel()
 {
-   if (mViewInfo.selectedRegion.isPoint())
+   const double lowerBound =
+      std::max(mViewInfo.selectedRegion.t0(), ScrollingLowerBoundTime());
+   const double denom =
+      mViewInfo.selectedRegion.t1() - lowerBound;
+   if (denom <= 0.0)
       return;
 
    // LL:  The "-1" is just a hack to get around an issue where zooming to
@@ -5058,8 +5066,7 @@ void AudacityProject::OnZoomSel()
    //      where the selected region may be scrolled off the left of the screen.
    //      I know this isn't right, but until the real rounding or 1-off issue is
    //      found, this will have to work.
-   Zoom(((mViewInfo.zoom * mViewInfo.screen) - 1) /
+   Zoom(((mViewInfo.zoom * mViewInfo.screen) - 1) / denom);
-        (mViewInfo.selectedRegion.t1() - mViewInfo.selectedRegion.t0()));
    TP_ScrollWindow(mViewInfo.selectedRegion.t0());
 }
 

src/Project.cpp

@@ -1459,9 +1459,16 @@ void AudacityProject::OnScrollRightButton(wxScrollEvent & event)
 }
 
 
+double AudacityProject::ScrollingLowerBoundTime() const
+{
+   return mScrollBeyondZero
+      ? std::min(mTracks->GetStartTime(), -mViewInfo.screen / 2.0)
+      : 0;
+}
+
 void AudacityProject::SetHorizontalThumb(double scrollto)
 {
-   const double timeOffset = mScrollBeyondZero ? mViewInfo.screen / 2.0 : 0;
+   const double timeOffset = -ScrollingLowerBoundTime();
    int pos = (int) (
       (scrollto + timeOffset) * mViewInfo.zoom * mViewInfo.sbarScale
    );
@@ -1544,10 +1551,10 @@ void AudacityProject::FixScrollbars()
    // so that any point within the union of the selection and the track duration
    // may be scrolled to the midline.
    // May add even more to the end, so that you can always scroll the starting time to zero.
+   const double lowerBound = ScrollingLowerBoundTime();
    const double additional = mScrollBeyondZero
-      ? halfScreen + std::max(halfScreen, mViewInfo.screen - LastTime)
+      ? -lowerBound + std::max(halfScreen, mViewInfo.screen - LastTime)
       : mViewInfo.screen / 4.0;
-   const double lowerBound = mScrollBeyondZero ? -halfScreen : 0.0;
 
    mViewInfo.total = LastTime + additional;
 
@@ -1823,11 +1830,8 @@ void AudacityProject::OnScroll(wxScrollEvent & WXUNUSED(event))
 {
    const wxInt64 hlast = mViewInfo.sbarH;
 
-   const wxInt64 offset = mScrollBeyondZero
+   const double lowerBound = ScrollingLowerBoundTime();
-      ? (0.5 + (mViewInfo.zoom * mViewInfo.screen / 2.0))
+   const wxInt64 offset = 0.5 + -lowerBound * mViewInfo.zoom;
-      : 0.0;
-   const double lowerBound = mScrollBeyondZero
-      ? -mViewInfo.screen / 2.0 : 0.0;
 
    mViewInfo.sbarH =
       (wxInt64)(mHsbar->GetThumbPosition() / mViewInfo.sbarScale) - offset;

src/Project.h

@@ -348,6 +348,7 @@ class AUDACITY_DLL_API AudacityProject:  public wxFrame,
 
    void SafeDisplayStatusMessage(const wxChar *msg);
 
+   double ScrollingLowerBoundTime() const;
    void SetHorizontalThumb(double scrollto);
 
    // TrackPanel access