more const in drawing functions

src/Project.cpp

@@ -1956,7 +1956,7 @@ void AudacityProject::FixScrollbars()
 
    auto LastTime = -std::numeric_limits<double>::max();
    auto &tracks = *GetTracks();
-   for (auto track : tracks) {
+   for (const Track *track : tracks) {
       // Iterate over pending changed tracks if present.
       {
          auto other =

src/TrackArtist.cpp

@@ -340,7 +340,7 @@ void TrackArtist::SetMargins(int left, int top, int right, int bottom)
 }
 
 void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
-                             TrackList * tracks,
+                             const TrackList * tracks,
                              Track * start,
                              const wxRegion & reg,
                              const wxRect & rect,
@@ -353,8 +353,8 @@ void TrackArtist::DrawTracks(TrackPanelDrawingContext &context,
 {
    wxRect trackRect = rect;
    wxRect stereoTrackRect;
-   TrackListIterator iter(tracks);
-   Track *t;
+   TrackListConstIterator iter(tracks);
+   const Track *t;
 
    bool hasSolo = false;
    for (t = iter.First(); t; t = iter.Next()) {

src/TrackArtist.h

@@ -55,7 +55,7 @@ class AUDACITY_DLL_API TrackArtist {
 
    void SetColours(int iColorIndex);
    void DrawTracks(TrackPanelDrawingContext &context,
-                   TrackList *tracks, Track *start,
+                   const TrackList *tracks, Track *start,
                    const wxRegion & reg,
                    const wxRect & rect, const wxRect & clip,
                    const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo,

src/TrackPanel.cpp

@@ -1192,7 +1192,7 @@ void TrackPanel::DrawEverythingElse(TrackPanelDrawingContext &context,
    trackRect.height = 0;   // for drawing background in no tracks case.
 
    VisibleTrackIterator iter(GetProject());
-   for (Track *t = iter.First(); t; t = iter.Next()) {
+   for (const Track *t = iter.First(); t; t = iter.Next()) {
       auto other = GetTracks()->FindPendingChangedTrack(t->GetId());
       if (other)
          t = other.get();
@@ -1215,7 +1215,7 @@ void TrackPanel::DrawEverythingElse(TrackPanelDrawingContext &context,
       // If the previous track is linked to this one but isn't on the screen
       // (and thus would have been skipped by VisibleTrackIterator) we need to
       // draw that track's border instead.
-      Track *borderTrack = t;
+      const Track *borderTrack = t;
       wxRect borderRect = rect;
 
       if (l && !t->GetLinked() && trackRect.y < 0)
@@ -1718,7 +1718,7 @@ void TrackInfo::Status2DrawFunction
 
 void TrackPanel::DrawOutside
 (TrackPanelDrawingContext &context,
- Track * t, const wxRect & rec)
+ const Track * t, const wxRect & rec)
 {
    auto dc = &context.dc;
    bool bIsWave = (t->GetKind() == Track::Wave);
@@ -1769,7 +1769,7 @@ void TrackPanel::DrawOutside
 // If linked to a following channel, also paint the separator area, which
 // overlaps the next track rectangle's top
 void TrackPanel::DrawOutsideOfTrack
-(TrackPanelDrawingContext &context, Track * t, const wxRect & rect)
+(TrackPanelDrawingContext &context, const Track * t, const wxRect & rect)
 {
    auto dc = &context.dc;
 
@@ -2032,7 +2032,7 @@ void TrackPanel::VerticalScroll( float fracPosition){
 // Given rectangle excludes the insets left, right, and top
 // Draw a rectangular border and also a vertical separator of track controls
 // from the rest (ruler and proper track area)
-void TrackPanel::DrawBordersAroundTrack(Track * t, wxDC * dc,
+void TrackPanel::DrawBordersAroundTrack(const Track * t, wxDC * dc,
                                         const wxRect & rect, const int labelw,
                                         const int vrul)
 {
@@ -2064,7 +2064,7 @@ void TrackPanel::DrawBordersAroundTrack(Track * t, wxDC * dc,
 // Given rectangle has insets subtracted left, right, and top
 // Stroke lines along bottom and right, which are slightly short at
 // bottom-left and top-right
-void TrackPanel::DrawShadow(Track * /* t */ , wxDC * dc, const wxRect & rect)
+void TrackPanel::DrawShadow(const Track * /* t */ , wxDC * dc, const wxRect & rect)
 {
    int right = rect.x + rect.width - 1;
    int bottom = rect.y + rect.height - 1;

src/TrackPanel.h

@@ -375,14 +375,14 @@ protected:
                            const wxRect & clip);
    void DrawOutside
       (TrackPanelDrawingContext &context,
-       Track *t, const wxRect & rec);
+       const Track *t, const wxRect & rec);
 
    void HighlightFocusedTrack (wxDC* dc, const wxRect &rect);
-   void DrawShadow            (Track *t, wxDC* dc, const wxRect & rect);
-   void DrawBordersAroundTrack(Track *t, wxDC* dc, const wxRect & rect, const int labelw, const int vrul);
+   void DrawShadow            (const Track *t, wxDC* dc, const wxRect & rect);
+   void DrawBordersAroundTrack(const Track *t, wxDC* dc, const wxRect & rect, const int labelw, const int vrul);
    void DrawOutsideOfTrack
       (TrackPanelDrawingContext &context,
-       Track *t, const wxRect & rect);
+       const Track *t, const wxRect & rect);
 
 public:
    // Set the object that performs catch-all event handling when the pointer

src/TrackPanelAx.cpp

@@ -137,7 +137,7 @@ std::shared_ptr<Track> TrackPanelAx::SetFocus( std::shared_ptr<Track> track )
 }
 
 // Returns TRUE if passed track has the focus
-bool TrackPanelAx::IsFocused( Track *track )
+bool TrackPanelAx::IsFocused( const Track *track )
 {
    auto focusedTrack = mFocusedTrack.lock();
    if( !focusedTrack )

src/TrackPanelAx.h

@@ -40,7 +40,7 @@ public:
    std::shared_ptr<Track> SetFocus( std::shared_ptr<Track> track = {} );
 
    // Returns TRUE if passed track has the focus
-   bool IsFocused( Track *track );
+   bool IsFocused( const Track *track );
 
    // Called to signal changes to a track
    void Updated();