Bug1197, yet again: extreme zoom-in behavior, now Mac specific: ...

...fix differing results on Mac by calculating only in double, so that selection
remains centered at extreme zoom-in for long projects (about 20 min.) and
selection after about 15 min.

src/Project.cpp

@@ -1513,24 +1513,23 @@ double AudacityProject::ScrollingLowerBoundTime() const
    return std::min(mTracks->GetStartTime(), -screen / 2.0);
 }
 
-wxInt64 AudacityProject::PixelWidthBeforeTime(double scrollto) const
+// PRL: Bug1197: we seem to need to compute all in double, to avoid differing results on Mac
+// That's why ViewInfo::TimeRangeToPixelWidth was defined, with some regret.
+double AudacityProject::PixelWidthBeforeTime(double scrollto) const
 {
    const double lowerBound = ScrollingLowerBoundTime();
    return
-      mViewInfo.TimeToPosition(scrollto, 0
-      , true
-      ) -
-      mViewInfo.TimeToPosition(lowerBound, 0
-      , true
-      );
+      // Ignoring fisheye is correct here
+      mViewInfo.TimeRangeToPixelWidth(scrollto - lowerBound);
 }
 
 void AudacityProject::SetHorizontalThumb(double scrollto)
 {
-   wxInt64 max = mHsbar->GetRange() - mHsbar->GetThumbSize();
-   int pos = std::min(max,
-                std::max(wxInt64(0),
-                   wxInt64(PixelWidthBeforeTime(scrollto) * mViewInfo.sbarScale)));
+   const int max = mHsbar->GetRange() - mHsbar->GetThumbSize();
+   const int pos =
+      std::min(max,
+         std::max(0,
+            int(floor(0.5 + PixelWidthBeforeTime(scrollto) * mViewInfo.sbarScale))));
    mHsbar->SetThumbPosition(pos);
 }
 
@@ -1704,7 +1703,8 @@ void AudacityProject::FixScrollbars()
       int scaledSbarH = (int)(mViewInfo.sbarH * mViewInfo.sbarScale);
       int scaledSbarScreen = (int)(mViewInfo.sbarScreen * mViewInfo.sbarScale);
       int scaledSbarTotal = (int)(mViewInfo.sbarTotal * mViewInfo.sbarScale);
-      const int offset = mViewInfo.sbarScale * PixelWidthBeforeTime(0.0);
+      const int offset =
+         int(floor(0.5 + mViewInfo.sbarScale * PixelWidthBeforeTime(0.0)));
 
       mHsbar->SetScrollbar(scaledSbarH + offset, scaledSbarScreen, scaledSbarTotal,
          scaledSbarScreen, TRUE);

src/Project.h

@@ -384,7 +384,8 @@ class AUDACITY_DLL_API AudacityProject:  public wxFrame,
 
    double ScrollingLowerBoundTime() const;
    // How many pixels are covered by the period from lowermost scrollable time, to the given time:
-   wxInt64 PixelWidthBeforeTime(double scrollto) const;
+   // PRL: Bug1197: we seem to need to compute all in double, to avoid differing results on Mac
+   double PixelWidthBeforeTime(double scrollto) const;
    void SetHorizontalThumb(double scrollto);
 
    // TrackPanel access

src/ViewInfo.cpp

@@ -63,6 +63,13 @@ wxInt64 ZoomInfo::TimeToPosition(double projectTime,
    );
 }
 
+// This always ignores the fisheye.  Use with caution!
+// You should prefer to call TimeToPosition twice, for endpoints, and take the difference!
+double ZoomInfo::TimeRangeToPixelWidth(double timeRange) const
+{
+   return timeRange * zoom;
+}
+
 bool ZoomInfo::ZoomInAvailable() const
 {
    return zoom < gMaxZoom;

src/ViewInfo.h

@@ -62,6 +62,10 @@ public:
       , bool ignoreFisheye = false
    ) const;
 
+   // This always ignores the fisheye.  Use with caution!
+   // You should prefer to call TimeToPosition twice, for endpoints, and take the difference!
+   double TimeRangeToPixelWidth(double timeRange) const;
+
    double OffsetTimeByPixels(double time, wxInt64 offset, bool ignoreFisheye = false) const
    {
       return PositionToTime(offset + TimeToPosition(time, ignoreFisheye), ignoreFisheye);