ViewInfo has a base class, ZoomInfo, containing only what TrackArtist needs besides the SelectedRegion

src/ViewInfo.cpp

@@ -13,21 +13,29 @@ Paul Licameli
 #include "Internat.h"
 #include "xml/XMLWriter.h"
 
-ViewInfo::ViewInfo(double start, double screenDuration, double pixelsPerSecond)
-   : selectedRegion()
-   , track(0)
-   , vpos(0)
+ZoomInfo::ZoomInfo(double start, double screenDuration, double pixelsPerSecond)
+   : vpos(0)
    , h(start)
    , screen(screenDuration)
-   , total(screen)
    , zoom(pixelsPerSecond)
+{
+}
 
+ZoomInfo::~ZoomInfo()
+{
+}
+
+
+ViewInfo::ViewInfo(double start, double screenDuration, double pixelsPerSecond)
+   : ZoomInfo(start, screenDuration, pixelsPerSecond)
+   , selectedRegion()
+   , track(NULL)
+   , total(screen)
    , sbarH(0)
    , sbarScreen(1)
    , sbarTotal(1)
    , sbarScale(1.0)
    , scrollStep(16)
-
    , bUpdateTrackIndicator(true)
 {
 }

src/ViewInfo.h

@@ -18,10 +18,28 @@ const double gMaxZoom = 6000000,
 
 class Track;
 
-class AUDACITY_DLL_API ViewInfo
+
+// The subset of ViewInfo information (other than selection)
+// that is sufficient for purposes of TrackArtist,
+// and for computing conversions between track times and pixel positions.
+class AUDACITY_DLL_API ZoomInfo
 {
 public:
+   ZoomInfo(double start, double duration, double pixelsPerSecond);
+   ~ZoomInfo();
 
+   int vpos;                    // vertical scroll pos
+
+   double h;                    // h pos in secs
+
+   double screen;               // screen width in secs
+   double zoom;                 // pixels per second
+};
+
+class AUDACITY_DLL_API ViewInfo
+   : public ZoomInfo
+{
+public:
    ViewInfo(double start, double screenDuration, double pixelsPerSecond);
 
    // Current selection
@@ -31,13 +49,8 @@ public:
    // Scroll info
 
    Track *track;                // first visible track
-   int vpos;                    // vertical scroll pos
 
-   double h;                    // h pos in secs
-   double screen;               // screen width in secs
    double total;                // total width in secs
-   double zoom;                 // pixels per second
-
    // Current horizontal scroll bar positions, in pixels
    wxInt64 sbarH;
    wxInt64 sbarScreen;