diff --git a/src/Envelope.cpp b/src/Envelope.cpp
index 3ce97819f..3d563c6e5 100644
--- a/src/Envelope.cpp
+++ b/src/Envelope.cpp
@@ -186,7 +186,7 @@ static void DrawPoint(wxDC & dc, const wxRect & r, int x, int y, bool top)
 /// TODO: This should probably move to track artist.
 void Envelope::DrawPoints(wxDC & dc, const wxRect & r, const ZoomInfo &zoomInfo,
                     bool dB, double dBRange,
-                    float zoomMin, float zoomMax)
+                    float zoomMin, float zoomMax) const
 {
    dc.SetPen(AColor::envelopePen);
    dc.SetBrush(*wxWHITE_BRUSH);
@@ -1151,7 +1151,7 @@ void Envelope::GetValues
       buffer[xx] = GetValue(zoomInfo.PositionToTime(xx, -leftOffset));
 }
 
-int Envelope::NumberOfPointsAfter(double t)
+int Envelope::NumberOfPointsAfter(double t) const
 {
    if( t >= mEnv[mEnv.size()-1].GetT() )
       return 0;
@@ -1169,7 +1169,7 @@ int Envelope::NumberOfPointsAfter(double t)
    }
 }
 
-double Envelope::NextPointAfter(double t)
+double Envelope::NextPointAfter(double t) const
 {
    if( mEnv[mEnv.size()-1].GetT() < t )
       return t;
@@ -1186,7 +1186,7 @@ double Envelope::NextPointAfter(double t)
    }
 }
 
-double Envelope::Average( double t0, double t1 )
+double Envelope::Average( double t0, double t1 ) const
 {
   if( t0 == t1 )
     return GetValue( t0 );
@@ -1194,7 +1194,7 @@ double Envelope::Average( double t0, double t1 )
     return Integral( t0, t1 ) / (t1 - t0);
 }
 
-double Envelope::AverageOfInverse( double t0, double t1 )
+double Envelope::AverageOfInverse( double t0, double t1 ) const
 {
   if( t0 == t1 )
     return 1.0 / GetValue( t0 );
@@ -1285,7 +1285,7 @@ static double SolveIntegrateInverseInterpolated(double y1, double y2, double tim
 
 // We should be able to write a very efficient memoizer for this
 // but make sure it gets reset when the envelope is changed.
-double Envelope::Integral( double t0, double t1 )
+double Envelope::Integral( double t0, double t1 ) const
 {
    if(t0 == t1)
       return 0.0;
@@ -1345,7 +1345,7 @@ double Envelope::Integral( double t0, double t1 )
    }
 }
 
-double Envelope::IntegralOfInverse( double t0, double t1 )
+double Envelope::IntegralOfInverse( double t0, double t1 ) const
 {
    if(t0 == t1)
       return 0.0;
@@ -1405,7 +1405,7 @@ double Envelope::IntegralOfInverse( double t0, double t1 )
    }
 }
 
-double Envelope::SolveIntegralOfInverse( double t0, double area )
+double Envelope::SolveIntegralOfInverse( double t0, double area ) const
 {
    if(area == 0.0)
       return t0;
@@ -1503,7 +1503,7 @@ double Envelope::SolveIntegralOfInverse( double t0, double area )
    }
 }
 
-void Envelope::print()
+void Envelope::print() const
 {
    for( unsigned int i = 0; i < mEnv.size(); i++ )
       printf( "(%.2f, %.2f)\n", mEnv[i].GetT(), mEnv[i].GetVal() );
diff --git a/src/Envelope.h b/src/Envelope.h
index e3816087a..1e8c017d2 100644
--- a/src/Envelope.h
+++ b/src/Envelope.h
@@ -108,7 +108,7 @@ class Envelope final : public XMLTagHandler {
 
    void DrawPoints(wxDC & dc, const wxRect & r, const ZoomInfo &zoomInfo,
              bool dB, double dBRange,
-             float zoomMin, float zoomMax);
+             float zoomMin, float zoomMax) const;
 
    // Event Handlers
    // Each ofthese returns true if parents needs to be redrawn
@@ -149,16 +149,16 @@ class Envelope final : public XMLTagHandler {
    void GetValues
       (double *buffer, int bufferLen, int leftOffset, const ZoomInfo &zoomInfo) const;
 
-   int NumberOfPointsAfter(double t);
-   double NextPointAfter(double t);
+   int NumberOfPointsAfter(double t) const;
+   double NextPointAfter(double t) const;
 
-   double Average( double t0, double t1 );
-   double AverageOfInverse( double t0, double t1 );
-   double Integral( double t0, double t1 );
-   double IntegralOfInverse( double t0, double t1 );
-   double SolveIntegralOfInverse( double t0, double area);
+   double Average( double t0, double t1 ) const;
+   double AverageOfInverse( double t0, double t1 ) const;
+   double Integral( double t0, double t1 ) const;
+   double IntegralOfInverse( double t0, double t1 ) const;
+   double SolveIntegralOfInverse( double t0, double area) const;
 
-   void print();
+   void print() const;
    void testMe();
 
    bool IsDirty() const;
diff --git a/src/LabelTrack.cpp b/src/LabelTrack.cpp
index 25ced4d3c..0dcb42e60 100644
--- a/src/LabelTrack.cpp
+++ b/src/LabelTrack.cpp
@@ -315,7 +315,7 @@ void LabelTrack::ResetFont()
 /// take priority over the ones earlier, so because centering
 /// is the first thing we do, it's the first thing we lose if
 /// we can't do everything we want to.
-void LabelTrack::ComputeTextPosition(const wxRect & r, int index)
+void LabelTrack::ComputeTextPosition(const wxRect & r, int index) const
 {
    // xExtra is extra space
    // between the text and the endpoints.
@@ -457,7 +457,7 @@ void LabelTrack::ComputeTextPosition(const wxRect & r, int index)
 /// ComputeLayout determines which row each label
 /// should be placed on, and reserves space for it.
 /// Function assumes that the labels are sorted.
-void LabelTrack::ComputeLayout(const wxRect & r, const ZoomInfo &zoomInfo)
+void LabelTrack::ComputeLayout(const wxRect & r, const ZoomInfo &zoomInfo) const
 {
    int i;
    int iRow;
@@ -710,7 +710,7 @@ void LabelStruct::DrawHighlight( wxDC & dc, int xPos1, int xPos2, int charHeight
       dc.DrawRectangle(xPos2-1, y-charHeight/2, xPos1-xPos2+1, charHeight);
 }
 
-void LabelStruct::getXPos( wxDC & dc, int * xPos1, int cursorPos)
+void LabelStruct::getXPos( wxDC & dc, int * xPos1, int cursorPos) const
 {
    *xPos1 = xText;
    if( cursorPos > 0)
@@ -744,7 +744,7 @@ bool LabelTrack::CalcCursorX(wxWindow * parent, int * x)
 ///   @param  r  the LabelTrack rectangle.
 void LabelTrack::Draw(wxDC & dc, const wxRect & r,
    const SelectedRegion &selectedRegion,
-   const ZoomInfo &zoomInfo)
+   const ZoomInfo &zoomInfo) const
 {
    if(msFont.Ok())
       dc.SetFont(msFont);
@@ -881,7 +881,7 @@ void LabelTrack::Draw(wxDC & dc, const wxRect & r,
 /// Set the cursor position according to x position of mouse
 /// uses GetTextExtent to find the character position
 /// corresponding to the x pixel position.
-void LabelTrack::SetCurrentCursorPosition(wxDC & dc, int xPos)
+void LabelTrack::SetCurrentCursorPosition(wxDC & dc, int xPos) const
 {
    // A bool indicator to see if set the cursor position or not
    bool finished = false;
@@ -925,7 +925,7 @@ void LabelTrack::SetCurrentCursorPosition(wxDC & dc, int xPos)
    }
 }
 
-void LabelTrack::calculateFontHeight(wxDC & dc)
+void LabelTrack::calculateFontHeight(wxDC & dc) const
 {
    int charDescent;
    int charLeading;
diff --git a/src/LabelTrack.h b/src/LabelTrack.h
index 35e836148..3df894c8d 100644
--- a/src/LabelTrack.h
+++ b/src/LabelTrack.h
@@ -56,7 +56,7 @@ public:
    void DrawText( wxDC & dc, const wxRect & r);
    void DrawTextBox( wxDC & dc, const wxRect & r);
    void DrawHighlight( wxDC & dc, int xPos1, int xPos2, int charHeight);
-   void getXPos( wxDC & dc, int * xPos1, int cursorPos);
+   void getXPos( wxDC & dc, int * xPos1, int cursorPos) const;
    const SelectedRegion &getSelectedRegion() const { return selectedRegion; }
    double getDuration() const { return selectedRegion.duration(); }
    double getT0() const { return selectedRegion.t0(); }
@@ -128,7 +128,7 @@ class AUDACITY_DLL_API LabelTrack final : public Track
 
    void Draw(wxDC & dc, const wxRect & r,
              const SelectedRegion &selectedRegion,
-             const ZoomInfo &zoomInfo);
+             const ZoomInfo &zoomInfo) const;
 
    int getSelectedIndex() const { return mSelIndex; }
    bool IsAdjustingLabel() const { return mIsAdjustingLabel; }
@@ -258,29 +258,29 @@ class AUDACITY_DLL_API LabelTrack final : public Track
    static bool mbGlyphsReady;
    static wxBitmap mBoundaryGlyphs[NUM_GLYPH_CONFIGS * NUM_GLYPH_HIGHLIGHTS];
 
-   int xUsed[MAX_NUM_ROWS];
+   mutable int xUsed[MAX_NUM_ROWS];
 
    static int mFontHeight;
-   int mXPos1;                         /// left X pos of highlighted area
-   int mXPos2;                         /// right X pos of highlighted area
-   int mCurrentCursorPos;              /// current cursor position
-   int mInitialCursorPos;              /// initial cursor position
-   double mMouseXPos;                  /// mouse X pos
+   mutable int mXPos1;                         /// left X pos of highlighted area
+   mutable int mXPos2;                         /// right X pos of highlighted area
+   mutable int mCurrentCursorPos;              /// current cursor position
+   mutable int mInitialCursorPos;              /// initial cursor position
+   mutable double mMouseXPos;                  /// mouse X pos
    int mDragXPos;                      /// end X pos of dragging
    bool mInBox;                        /// flag to tell if the mouse is in text box
-   bool mResetCursorPos;               /// flag to reset cursor position(used in the dragging the glygh)
+   mutable bool mResetCursorPos;               /// flag to reset cursor position(used in the dragging the glygh)
    bool mRightDragging;                /// flag to tell if it's a valid dragging
-   bool mDrawCursor;                   /// flag to tell if drawing the cursor or not
+   mutable bool mDrawCursor;                   /// flag to tell if drawing the cursor or not
    int mRestoreFocus;              /// Restore focus to this track when done editing
 
    // Set in copied label tracks
    double mClipLen;
 
-   void ComputeLayout(const wxRect & r, const ZoomInfo &zoomInfo);
-   void ComputeTextPosition(const wxRect & r, int index);
-   void SetCurrentCursorPosition(wxDC & dc, int xPos);
+   void ComputeLayout(const wxRect & r, const ZoomInfo &zoomInfo) const;
+   void ComputeTextPosition(const wxRect & r, int index) const;
+   void SetCurrentCursorPosition(wxDC & dc, int xPos) const;
 
-   void calculateFontHeight(wxDC & dc);
+   void calculateFontHeight(wxDC & dc) const;
    void RemoveSelectedText();
 
    bool mIsAdjustingLabel;
diff --git a/src/NoteTrack.h b/src/NoteTrack.h
index e848bb529..23da96a05 100644
--- a/src/NoteTrack.h
+++ b/src/NoteTrack.h
@@ -116,7 +116,7 @@ class AUDACITY_DLL_API NoteTrack final : public Track {
    // call this once before a series of calls to IPitchToY(). It
    // sets mBottom to offset of octave 0 so that mBottomNote
    // is located at r.y + r.height - (GetNoteMargin() + 1 + mPitchHeight)
-   void PrepareIPitchToY(const wxRect &r) {
+   void PrepareIPitchToY(const wxRect &r) const {
        mBottom = r.y + r.height - GetNoteMargin() - 1 - mPitchHeight +
           (mBottomNote / 12) * GetOctaveHeight() +
           GetNotePos(mBottomNote % 12);
@@ -197,7 +197,7 @@ class AUDACITY_DLL_API NoteTrack final : public Track {
    // mSeq variable. (TrackArtist should check to make sure this
    // flip-flop from mSeq to mSerializationBuffer happened an
    // even number of times, otherwise mSeq will be NULL).
-   char *mSerializationBuffer; // NULL means no buffer
+   mutable char *mSerializationBuffer; // NULL means no buffer
    long mSerializationLength;
 
    DirManager *mDirManager;
@@ -207,7 +207,7 @@ class AUDACITY_DLL_API NoteTrack final : public Track {
 #endif
 
    // mBottom is the Y offset of pitch 0 (normally off screen)
-   int mBottom;
+   mutable int mBottom;
    int mBottomNote;
    int mStartBottomNote;
    int mPitchHeight;
diff --git a/src/TimeTrack.cpp b/src/TimeTrack.cpp
index ab8bb1b8c..ce1dbb0e1 100644
--- a/src/TimeTrack.cpp
+++ b/src/TimeTrack.cpp
@@ -124,17 +124,17 @@ void TimeTrack::SetInterpolateLog(bool interpolateLog) {
 }
 
 //Compute the (average) warp factor between two non-warped time points
-double TimeTrack::ComputeWarpFactor(double t0, double t1)
+double TimeTrack::ComputeWarpFactor(double t0, double t1) const
 {
    return GetEnvelope()->AverageOfInverse(t0, t1);
 }
 
-double TimeTrack::ComputeWarpedLength(double t0, double t1)
+double TimeTrack::ComputeWarpedLength(double t0, double t1) const
 {
    return GetEnvelope()->IntegralOfInverse(t0, t1);
 }
 
-double TimeTrack::SolveWarpedLength(double t0, double length)
+double TimeTrack::SolveWarpedLength(double t0, double length) const
 {
    return GetEnvelope()->SolveIntegralOfInverse(t0, length);
 }
@@ -229,7 +229,7 @@ void TimeTrack::WriteXML(XMLWriter &xmlFile)
    xmlFile.EndTag(wxT("timetrack"));
 }
 
-void TimeTrack::Draw(wxDC & dc, const wxRect & r, const ZoomInfo &zoomInfo)
+void TimeTrack::Draw(wxDC & dc, const wxRect & r, const ZoomInfo &zoomInfo) const
 {
    double min = zoomInfo.PositionToTime(0);
    double max = zoomInfo.PositionToTime(r.width);
diff --git a/src/TimeTrack.h b/src/TimeTrack.h
index 88e0bb8ae..506b434b2 100644
--- a/src/TimeTrack.h
+++ b/src/TimeTrack.h
@@ -50,7 +50,7 @@ class TimeTrack final : public Track {
    double GetStartTime() const override { return 0.0; }
    double GetEndTime() const override { return 0.0; }
 
-   void Draw(wxDC & dc, const wxRect & r, const ZoomInfo &zoomInfo);
+   void Draw(wxDC & dc, const wxRect & r, const ZoomInfo &zoomInfo) const;
 
    // XMLTagHandler callback methods for loading and saving
 
@@ -68,6 +68,7 @@ class TimeTrack final : public Track {
    // Access the track's speed envelope
 
    Envelope *GetEnvelope() { return mEnvelope; }
+   const Envelope *GetEnvelope() const { return mEnvelope; }
 
    //Note: The meaning of this function has changed (December 2012)
    //Previously this function did something that was close to the opposite (but not entirely accurate).
@@ -81,7 +82,7 @@ class TimeTrack final : public Track {
     * @param t1 The ending time to calculate to
     * @return The relative length increase of the chosen segment from the original sound.
     */
-   double ComputeWarpFactor(double t0, double t1);
+   double ComputeWarpFactor(double t0, double t1) const;
    /** @brief Compute the duration (in seconds at playback) of the specified region of the track.
     *
     * Takes a region of the time track (specified by the unwarped time points in the project), and
@@ -91,7 +92,7 @@ class TimeTrack final : public Track {
     * @param t1 unwarped time to stop calculation at
     * @return the warped duration in seconds
     */
-   double ComputeWarpedLength(double t0, double t1);
+   double ComputeWarpedLength(double t0, double t1) const;
    /** @brief Compute how much unwarped time must have elapsed if length seconds of warped time has
     * elapsed
     *
@@ -99,7 +100,7 @@ class TimeTrack final : public Track {
     * @param length How many seconds of warped time went past.
     * @return The end point (in seconds from project start) as unwarped time
     */
-   double SolveWarpedLength(double t0, double length);
+   double SolveWarpedLength(double t0, double length) const;
 
    // Get/Set the speed-warping range, as percentage of original speed (e.g. 90%-110%)
 
diff --git a/src/TrackArtist.cpp b/src/TrackArtist.cpp
index b8c8d0961..6bb47a5c5 100644
--- a/src/TrackArtist.cpp
+++ b/src/TrackArtist.cpp
@@ -1306,7 +1306,7 @@ void TrackArtist::DrawMinMaxRMS(wxDC &dc, const wxRect & rect, const double env[
 void TrackArtist::DrawIndividualSamples(wxDC &dc, int leftOffset, const wxRect &rect,
                                         float zoomMin, float zoomMax,
                                         bool dB, float dBRange,
-                                        WaveClip *clip,
+                                        const WaveClip *clip,
                                         const ZoomInfo &zoomInfo,
                                         bool bigPoints, bool showPoints, bool muted)
 {
@@ -1457,7 +1457,7 @@ void TrackArtist::DrawEnvLine(wxDC &dc, const wxRect &rect, int x0, int y0, int
    }
 }
 
-void TrackArtist::DrawWaveform(WaveTrack *track,
+void TrackArtist::DrawWaveform(const WaveTrack *track,
                                wxDC & dc,
                                const wxRect & rect,
                                const SelectedRegion &selectedRegion,
@@ -1472,7 +1472,8 @@ void TrackArtist::DrawWaveform(WaveTrack *track,
    DrawBackgroundWithSelection(&dc, rect, track, blankSelectedBrush, blankBrush,
          selectedRegion, zoomInfo);
 
-   for (WaveClipList::compatibility_iterator it = track->GetClipIterator(); it; it = it->GetNext())
+   for (WaveClipList::compatibility_iterator it =
+      const_cast<WaveTrack*>(track)->GetClipIterator(); it; it = it->GetNext())
       DrawClipWaveform(track, it->GetData(), dc, rect, selectedRegion, zoomInfo,
                        drawEnvelope, bigPoints,
                        dB, muted);
@@ -1718,8 +1719,8 @@ void FindWavePortions
 }
 }
 
-void TrackArtist::DrawClipWaveform(WaveTrack *track,
-                                   WaveClip *clip,
+void TrackArtist::DrawClipWaveform(const WaveTrack *track,
+                                   const WaveClip *clip,
                                    wxDC & dc,
                                    const wxRect & rect,
                                    const SelectedRegion &selectedRegion,
@@ -2001,7 +2002,7 @@ void TrackArtist::DrawTimeSlider(wxDC & dc,
 }
 
 
-void TrackArtist::DrawSpectrum(WaveTrack *track,
+void TrackArtist::DrawSpectrum(const WaveTrack *track,
                                wxDC & dc,
                                const wxRect & rect,
                                const SelectedRegion &selectedRegion,
@@ -2011,7 +2012,8 @@ void TrackArtist::DrawSpectrum(WaveTrack *track,
          selectedRegion, zoomInfo);
 
    WaveTrackCache cache(track);
-   for (WaveClipList::compatibility_iterator it = track->GetClipIterator(); it; it = it->GetNext()) {
+   for (WaveClipList::compatibility_iterator it =
+      const_cast<WaveTrack*>(track)->GetClipIterator(); it; it = it->GetNext()) {
       DrawClipSpectrum(cache, it->GetData(), dc, rect, selectedRegion, zoomInfo);
    }
 }
@@ -2099,7 +2101,7 @@ AColor::ColorGradientChoice ChooseColorSet( float bin0, float bin1, float selBin
 
 
 void TrackArtist::DrawClipSpectrum(WaveTrackCache &waveTrackCache,
-                                   WaveClip *clip,
+                                   const WaveClip *clip,
                                    wxDC & dc,
                                    const wxRect & rect,
                                    const SelectedRegion &selectedRegion,
@@ -2669,7 +2671,7 @@ int PitchToY(double p, int bottom)
    sel is equal to rect, and the entire region is drawn with unselected
    background colors.
  */
-void TrackArtist::DrawNoteBackground(NoteTrack *track, wxDC &dc,
+void TrackArtist::DrawNoteBackground(const NoteTrack *track, wxDC &dc,
                                      const wxRect &rect, const wxRect &sel,
                                      const ZoomInfo &zoomInfo,
                                      const wxBrush &wb, const wxPen &wp,
@@ -2763,7 +2765,7 @@ graphics. Since there may be notes outside of the display region,
 reserve a half-note-height margin at the top and bottom of the
 window and draw out-of-bounds notes here instead.
 */
-void TrackArtist::DrawNoteTrack(NoteTrack *track,
+void TrackArtist::DrawNoteTrack(const NoteTrack *track,
                                 wxDC & dc,
                                 const wxRect & rect,
                                 const SelectedRegion &selectedRegion,
@@ -2786,7 +2788,7 @@ void TrackArtist::DrawNoteTrack(NoteTrack *track,
       Alg_track_ptr alg_track = Alg_seq::unserialize(track->mSerializationBuffer,
             track->mSerializationLength);
       assert(alg_track->get_type() == 's');
-      track->mSeq = seq = (Alg_seq_ptr) alg_track;
+      const_cast<NoteTrack*>(track)->mSeq = seq = (Alg_seq_ptr) alg_track;
       free(track->mSerializationBuffer);
       track->mSerializationBuffer = NULL;
    }
@@ -3133,7 +3135,7 @@ void TrackArtist::DrawNoteTrack(NoteTrack *track,
 #endif // USE_MIDI
 
 
-void TrackArtist::DrawLabelTrack(LabelTrack *track,
+void TrackArtist::DrawLabelTrack(const LabelTrack *track,
                                  wxDC & dc,
                                  const wxRect & rect,
                                  const SelectedRegion &selectedRegion,
@@ -3148,7 +3150,7 @@ void TrackArtist::DrawLabelTrack(LabelTrack *track,
    track->Draw(dc, rect, SelectedRegion(sel0, sel1), zoomInfo);
 }
 
-void TrackArtist::DrawTimeTrack(TimeTrack *track,
+void TrackArtist::DrawTimeTrack(const TimeTrack *track,
                                 wxDC & dc,
                                 const wxRect & rect,
                                 const ZoomInfo &zoomInfo)
@@ -3293,7 +3295,7 @@ void TrackArtist::DrawSyncLockTiles(wxDC *dc, wxRect rect)
 }
 
 void TrackArtist::DrawBackgroundWithSelection(wxDC *dc, const wxRect &rect,
-   Track *track, wxBrush &selBrush, wxBrush &unselBrush,
+   const Track *track, wxBrush &selBrush, wxBrush &unselBrush,
    const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo)
 {
    //MM: Draw background. We should optimize that a bit more.
diff --git a/src/TrackArtist.h b/src/TrackArtist.h
index 6fd98a2b6..e7dc920ad 100644
--- a/src/TrackArtist.h
+++ b/src/TrackArtist.h
@@ -84,7 +84,7 @@ class AUDACITY_DLL_API TrackArtist {
 
    // Helper: draws background with selection rect
    static void DrawBackgroundWithSelection(wxDC *dc, const wxRect &rect,
-         Track *track, wxBrush &selBrush, wxBrush &unselBrush,
+         const Track *track, wxBrush &selBrush, wxBrush &unselBrush,
          const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo);
 
  private:
@@ -93,46 +93,46 @@ class AUDACITY_DLL_API TrackArtist {
    // Lower-level drawing functions
    //
 
-   void DrawWaveform(WaveTrack *track,
+   void DrawWaveform(const WaveTrack *track,
                      wxDC & dc, const wxRect & rect,
                      const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo,
                      bool drawEnvelope, bool bigPoints, bool drawSliders,
                      bool muted);
 
-   void DrawSpectrum(WaveTrack *track,
+   void DrawSpectrum(const WaveTrack *track,
                      wxDC & dc, const wxRect & rect,
                      const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo);
 #ifdef USE_MIDI
    int GetBottom(NoteTrack *t, const wxRect &rect);
-   void DrawNoteBackground(NoteTrack *track, wxDC &dc,
+   void DrawNoteBackground(const NoteTrack *track, wxDC &dc,
                            const wxRect &rect, const wxRect &sel,
                            const ZoomInfo &zoomInfo,
                            const wxBrush &wb, const wxPen &wp,
                            const wxBrush &bb, const wxPen &bp,
                            const wxPen &mp);
-   void DrawNoteTrack(NoteTrack *track,
+   void DrawNoteTrack(const NoteTrack *track,
                       wxDC & dc, const wxRect & rect,
                       const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo,
                       bool muted);
 #endif // USE_MIDI
 
-   void DrawLabelTrack(LabelTrack *track,
+   void DrawLabelTrack(const LabelTrack *track,
                        wxDC & dc, const wxRect & rect,
                        const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo);
 
-   void DrawTimeTrack(TimeTrack *track,
+   void DrawTimeTrack(const TimeTrack *track,
                       wxDC & dc, const wxRect & rect, const ZoomInfo &zoomInfo);
 
    void DrawTimeSlider(wxDC & dc, const wxRect & rect,
                        bool rightwards);
 
-   void DrawClipWaveform(WaveTrack *track, WaveClip *clip,
+   void DrawClipWaveform(const WaveTrack *track, const WaveClip *clip,
                          wxDC & dc, const wxRect & rect,
                          const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo,
                          bool drawEnvelope, bool bigPoints,
                          bool dB, bool muted);
 
-   void DrawClipSpectrum(WaveTrackCache &cache, WaveClip *clip,
+   void DrawClipSpectrum(WaveTrackCache &cache, const WaveClip *clip,
                          wxDC & dc, const wxRect & rect,
                          const SelectedRegion &selectedRegion, const ZoomInfo &zoomInfo);
 
@@ -156,7 +156,7 @@ class AUDACITY_DLL_API TrackArtist {
    void DrawIndividualSamples(wxDC & dc, int leftOffset, const wxRect & rect,
                               float zoomMin, float zoomMax,
                               bool dB, float dBRange,
-                              WaveClip *clip,
+                              const WaveClip *clip,
                               const ZoomInfo &zoomInfo,
                               bool bigPoints, bool showPoints, bool muted);
 
diff --git a/src/WaveClip.cpp b/src/WaveClip.cpp
index fa35e4a2f..e00204dc1 100644
--- a/src/WaveClip.cpp
+++ b/src/WaveClip.cpp
@@ -502,7 +502,7 @@ fillWhere(std::vector<sampleCount> &where, int len, double bias, double correcti
 //
 
 bool WaveClip::GetWaveDisplay(WaveDisplay &display, double t0,
-                               double pixelsPerSecond, bool &isLoadingOD)
+                               double pixelsPerSecond, bool &isLoadingOD) const
 {
    const bool allocated = (display.where != 0);
 
@@ -1072,7 +1072,7 @@ void SpecCache::Populate
 bool WaveClip::GetSpectrogram(WaveTrackCache &waveTrackCache,
                               const float *& spectrogram, const sampleCount *& where,
                               int numPixels,
-                              double t0, double pixelsPerSecond)
+                              double t0, double pixelsPerSecond) const
 {
    const WaveTrack *const track = waveTrackCache.GetTrack();
    const SpectrogramSettings &settings = track->GetSpectrogramSettings();
@@ -1235,7 +1235,7 @@ void WaveClip::ClearDisplayRect()
    mDisplayRect.width = mDisplayRect.height = -1;
 }
 
-void WaveClip::SetDisplayRect(const wxRect& r)
+void WaveClip::SetDisplayRect(const wxRect& r) const
 {
    mDisplayRect = r;
 }
diff --git a/src/WaveClip.h b/src/WaveClip.h
index 599a0e695..bd8024819 100644
--- a/src/WaveClip.h
+++ b/src/WaveClip.h
@@ -265,6 +265,7 @@ public:
                    sampleCount start, sampleCount len);
 
    Envelope* GetEnvelope() { return mEnvelope; }
+   const Envelope* GetEnvelope() const { return mEnvelope; }
    BlockArray* GetSequenceBlockArray();
 
    // Get low-level access to the sequence. Whenever possible, don't use this,
@@ -283,18 +284,18 @@ public:
    /** Getting high-level data from the for screen display and clipping
     * calculations and Contrast */
    bool GetWaveDisplay(WaveDisplay &display,
-                       double t0, double pixelsPerSecond, bool &isLoadingOD);
+                       double t0, double pixelsPerSecond, bool &isLoadingOD) const;
    bool GetSpectrogram(WaveTrackCache &cache,
                        const float *& spectrogram, const sampleCount *& where,
                        int numPixels,
-                       double t0, double pixelsPerSecond);
+                       double t0, double pixelsPerSecond) const;
    bool GetMinMax(float *min, float *max, double t0, double t1);
    bool GetRMS(float *rms, double t0, double t1);
 
    // Set/clear/get rectangle that this WaveClip fills on screen. This is
    // called by TrackArtist while actually drawing the tracks and clips.
    void ClearDisplayRect();
-   void SetDisplayRect(const wxRect& r);
+   void SetDisplayRect(const wxRect& r) const;
    void GetDisplayRect(wxRect* r);
 
    /** Whenever you do an operation to the sequence that will change the number
@@ -373,14 +374,14 @@ public:
    void WriteXML(XMLWriter &xmlFile) /* not override */;
 
    // Cache of values to colour pixels of Spectrogram - used by TrackArtist
-   SpecPxCache    *mSpecPxCache;
+   mutable SpecPxCache    *mSpecPxCache;
 
    // AWD, Oct 2009: for pasting whitespace at the end of selection
    bool GetIsPlaceholder() const { return mIsPlaceholder; }
    void SetIsPlaceholder(bool val) { mIsPlaceholder = val; }
 
 protected:
-   wxRect mDisplayRect;
+   mutable wxRect mDisplayRect;
 
    double mOffset;
    int mRate;
@@ -389,9 +390,9 @@ protected:
    Sequence *mSequence;
    Envelope *mEnvelope;
 
-   WaveCache    *mWaveCache;
-   ODLock       mWaveCacheMutex;
-   SpecCache    *mSpecCache;
+   mutable WaveCache    *mWaveCache;
+   mutable ODLock       mWaveCacheMutex;
+   mutable SpecCache    *mSpecCache;
    SampleBuffer  mAppendBuffer;
    sampleCount   mAppendBufferLen;
 
diff --git a/src/WaveTrack.cpp b/src/WaveTrack.cpp
index 9c7275fd0..7ea2122be 100644
--- a/src/WaveTrack.cpp
+++ b/src/WaveTrack.cpp
@@ -2423,7 +2423,7 @@ bool WaveTrack::SplitAt(double t)
    return true;
 }
 
-void WaveTrack::UpdateLocationsCache()
+void WaveTrack::UpdateLocationsCache() const
 {
    unsigned int i;
    WaveClipArray clips;
@@ -2608,11 +2608,12 @@ static int SortClipArrayCmpFunc(WaveClip** clip1, WaveClip** clip2)
       return 1;
 }
 
-void WaveTrack::FillSortedClipArray(WaveClipArray& clips)
+void WaveTrack::FillSortedClipArray(WaveClipArray& clips) const
 {
    clips.Empty();
 
-   for (WaveClipList::compatibility_iterator it=GetClipIterator(); it; it=it->GetNext())
+   for (WaveClipList::compatibility_iterator it =
+      const_cast<WaveTrack*>(this)->GetClipIterator(); it; it=it->GetNext())
       clips.Add(it->GetData());
 
    clips.Sort(SortClipArrayCmpFunc);
diff --git a/src/WaveTrack.h b/src/WaveTrack.h
index 994ec0ffe..789150c27 100644
--- a/src/WaveTrack.h
+++ b/src/WaveTrack.h
@@ -342,7 +342,7 @@ class AUDACITY_DLL_API WaveTrack final : public Track {
 
    // Add all wave clips to the given array 'clips' and sort the array by
    // clip start time. The array is emptied prior to adding the clips.
-   void FillSortedClipArray(WaveClipArray& clips);
+   void FillSortedClipArray(WaveClipArray& clips) const;
 
    // Before calling 'Offset' on a clip, use this function to see if the
    // offsetting is allowed with respect to the other clips in this track.
@@ -373,7 +373,7 @@ class AUDACITY_DLL_API WaveTrack final : public Track {
    bool MergeClips(int clipidx1, int clipidx2);
 
    // Cache special locations (e.g. cut lines) for later speedy access
-   void UpdateLocationsCache();
+   void UpdateLocationsCache() const;
 
    // Get cached locations
    const std::vector<Location> &GetCachedLocations() const { return mDisplayLocationsCache; }
diff --git a/src/widgets/Ruler.cpp b/src/widgets/Ruler.cpp
index d74ecd10c..d2647e4ca 100644
--- a/src/widgets/Ruler.cpp
+++ b/src/widgets/Ruler.cpp
@@ -970,7 +970,7 @@ void Ruler::Update()
   Update(NULL);
 }
 
-void Ruler::Update(TimeTrack* timetrack)// Envelope *speedEnv, long minSpeed, long maxSpeed )
+void Ruler::Update(const TimeTrack* timetrack)// Envelope *speedEnv, long minSpeed, long maxSpeed )
 {
    const ZoomInfo *zoomInfo = NULL;
    if (!mLog && mOrientation == wxHORIZONTAL)
@@ -1295,7 +1295,7 @@ void Ruler::Draw(wxDC& dc)
    Draw( dc, NULL);
 }
 
-void Ruler::Draw(wxDC& dc, TimeTrack* timetrack)
+void Ruler::Draw(wxDC& dc, const TimeTrack* timetrack)
 {
    mDC = &dc;
    if( mLength <=0 )
diff --git a/src/widgets/Ruler.h b/src/widgets/Ruler.h
index c140e1996..d6846b01f 100644
--- a/src/widgets/Ruler.h
+++ b/src/widgets/Ruler.h
@@ -136,7 +136,7 @@ class AUDACITY_DLL_API Ruler {
 
    // Note that it will not erase for you...
    void Draw(wxDC& dc);
-   void Draw(wxDC& dc, TimeTrack* timetrack);
+   void Draw(wxDC& dc, const TimeTrack* timetrack);
    // If length <> 0, draws lines perpendiculars to ruler corresponding
    // to selected ticks (major, minor, or both), in an adjacent window.
    // You may need to use the offsets if you are using part of the dc for rulers, borders etc.
@@ -151,7 +151,7 @@ class AUDACITY_DLL_API Ruler {
 
  private:
    void Update();
-   void Update(TimeTrack* timetrack);
+   void Update(const TimeTrack* timetrack);
    void FindTickSizes();
    void FindLinearTickSizes(double UPP);
    wxString LabelString(double d, bool major);