Implement wxSlider ticks support in wxGTK

Tick marks were not available for wxSlider under GTK+ 2 or GTK+ 3
implementations of wxWidgets. However, tick marks have been available
for the GtkScale widget since GTK+ 2 version 2.16.

This change adds similar functionality in relation to tick marks
as was already available in wxMSW builds.

Closes https://github.com/wxWidgets/wxWidgets/pull/1355

include/wx/gtk/slider.h

@@ -56,6 +56,10 @@ public:
     virtual void SetThumbLength(int lenPixels) wxOVERRIDE;
     virtual int GetThumbLength() const wxOVERRIDE;
 
+    virtual void ClearTicks() wxOVERRIDE;
+    virtual void SetTick(int tickPos) wxOVERRIDE;
+    int GetTickFreq() const wxOVERRIDE;
+
     static wxVisualAttributes
     GetClassDefaultAttributes(wxWindowVariant variant = wxWINDOW_VARIANT_NORMAL);
 
@@ -73,11 +77,20 @@ protected:
     GtkWidget *m_minLabel,*m_maxLabel;
     bool m_blockScrollEvent;
 
+    // Note the following member is not used in GTK+2 < 2.16.
+    int m_tickFreq;
+
     virtual GdkWindow *GTKGetWindow(wxArrayGdkWindows& windows) const wxOVERRIDE;
 
     // set the slider value unconditionally
     void GTKSetValue(int value);
 
+    // Platform-specific implementation of SetTickFreq
+    virtual void DoSetTickFreq(int freq) wxOVERRIDE;
+
+private:
+    void Init();
+
     wxDECLARE_DYNAMIC_CLASS(wxSlider);
 };
 

interface/wx/slider.h

@@ -30,6 +30,8 @@
 
     On Windows, the track bar control is used.
 
+    On GTK+, tick marks are only available for version 2.16 and later.
+
     Slider generates the same events as wxScrollBar but in practice the most
     convenient way to process wxSlider updates is by handling the
     slider-specific @c wxEVT_SLIDER event which carries wxCommandEvent
@@ -41,7 +43,7 @@
     @style{wxSL_VERTICAL}
            Displays the slider vertically.
     @style{wxSL_AUTOTICKS}
-           Displays tick marks. Windows only.
+           Displays tick marks (Windows, GTK+ 2.16 and later).
     @style{wxSL_MIN_MAX_LABELS}
            Displays minimum, maximum labels (new since wxWidgets 2.9.1).
     @style{wxSL_VALUE_LABEL}
@@ -50,11 +52,11 @@
            Displays minimum, maximum and value labels (same as wxSL_VALUE_LABEL
            and wxSL_MIN_MAX_LABELS together).
     @style{wxSL_LEFT}
-           Displays ticks on the left and forces the slider to be vertical.
+           Displays ticks on the left and forces the slider to be vertical (Windows and GTK+ 3 only).
     @style{wxSL_RIGHT}
            Displays ticks on the right and forces the slider to be vertical.
     @style{wxSL_TOP}
-           Displays ticks on the top.
+           Displays ticks on the top (Windows and GTK+ 3 only).
     @style{wxSL_BOTTOM}
            Displays ticks on the bottom (this is the default).
     @style{wxSL_BOTH}
@@ -67,11 +69,11 @@
     @endStyleTable
 
     Notice that @c wxSL_LEFT, @c wxSL_TOP, @c wxSL_RIGHT and @c wxSL_BOTTOM
-    specify the position of the slider ticks in MSW implementation and that the
+    specify the position of the slider ticks and that the slider labels, if any,
-    slider labels, if any, are positioned on the opposite side. So, to have a
+    are positioned on the opposite side. So, to have a label on the left side of
-    label on the left side of a vertical slider, @b wxSL_RIGHT must be used (or
+    a vertical slider, @b wxSL_RIGHT must be used (or none of these styles at all
-    none of these styles at all should be specified as left and top are default
+    should be specified as left and top are default positions for the vertical
-    positions for the vertical and horizontal sliders respectively).
+    and horizontal sliders respectively).
 
     @beginEventEmissionTable{wxScrollEvent}
     You can use EVT_COMMAND_SCROLL... macros with window IDs for when intercepting
@@ -206,7 +208,7 @@ public:
     /**
         Clears the ticks.
 
-        @onlyfor{wxmsw}
+        @onlyfor{wxmsw,wxgtk}
     */
     virtual void ClearTicks();
 
@@ -278,7 +280,7 @@ public:
     /**
         Returns the tick frequency.
 
-        @onlyfor{wxmsw}
+        @onlyfor{wxmsw,wxgtk}
 
         @see SetTickFreq()
     */
@@ -372,7 +374,7 @@ public:
         @param tickPos
             The tick position.
 
-        @onlyfor{wxmsw}
+        @onlyfor{wxmsw,wxgtk}
 
         @see SetTickFreq()
     */
@@ -385,11 +387,11 @@ public:
             Frequency. For example, if the frequency is set to two, a tick mark is
             displayed for every other increment in the slider's range.
 
-        @onlyfor{wxmsw}
+        @onlyfor{wxmsw,wxgtk}
 
         @see GetTickFreq()
     */
-    virtual void SetTickFreq(int n);
+    virtual void SetTickFreq(int freq);
 
     /**
         Sets the slider position.

src/gtk/slider.cpp

@@ -273,7 +273,7 @@ static gchar* gtk_format_value(GtkScale*, double value, void*)
 
 wxSlider::wxSlider()
 {
-    m_scale = NULL;
+    Init();
 }
 
 wxSlider::~wxSlider()
@@ -282,6 +282,15 @@ wxSlider::~wxSlider()
         GTKDisconnect(m_scale);
 }
 
+void wxSlider::Init()
+{
+    m_scrollEventType = GTK_SCROLL_NONE;
+    m_needThumbRelease = false;
+    m_blockScrollEvent = false;
+    m_tickFreq = 0;
+    m_scale = NULL;
+}
+
 bool wxSlider::Create(wxWindow *parent,
                       wxWindowID id,
                       int value,
@@ -293,10 +302,8 @@ bool wxSlider::Create(wxWindow *parent,
                       const wxValidator& validator,
                       const wxString& name)
 {
+    Init();
     m_pos = value;
-    m_scrollEventType = GTK_SCROLL_NONE;
-    m_needThumbRelease = false;
-    m_blockScrollEvent = false;
 
     if (!PreCreation( parent, pos, size ) ||
         !CreateBase( parent, id, pos, size, style, validator, name ))
@@ -344,9 +351,9 @@ bool wxSlider::Create(wxWindow *parent,
     gtk_scale_set_draw_value(GTK_SCALE (m_scale), showValueLabel );
     if ( showValueLabel )
     {
-        // position the label appropriately: notice that wxSL_DIRECTION flags
+        // Position the label appropriately: notice that wxSL_DIRECTION flags
-        // specify the position of the ticks, not label, under MSW and so the
+        // specify the position of the ticks, not label, and so the
-        // label is on the opposite side
+        // label is on the opposite side.
         GtkPositionType posLabel;
         if ( style & wxSL_VERTICAL )
         {
@@ -501,6 +508,69 @@ int wxSlider::GetLineSize() const
     return int(gtk_adjustment_get_step_increment(adj));
 }
 
+void wxSlider::ClearTicks()
+{
+#if GTK_CHECK_VERSION(2,16,0)
+    if (wx_is_at_least_gtk2(16))
+        gtk_scale_clear_marks(GTK_SCALE (m_scale));
+#endif
+}
+
+void wxSlider::SetTick(int tickPos)
+{
+#if GTK_CHECK_VERSION(2,16,0)
+    if ( wx_is_at_least_gtk2(16) )
+    {
+        GtkPositionType posTicks;
+        long style = GetWindowStyle();
+
+        if ( style & wxSL_VERTICAL )
+        {
+            if ( style & wxSL_LEFT )
+                posTicks = GTK_POS_LEFT;
+            else
+                posTicks = GTK_POS_RIGHT;
+        }
+        else // horizontal slider
+        {
+            if ( style & wxSL_TOP )
+                posTicks = GTK_POS_TOP;
+            else
+                posTicks = GTK_POS_BOTTOM;
+        }
+
+        gtk_scale_add_mark(GTK_SCALE (m_scale), (double)tickPos, posTicks, NULL);
+    }
+#else
+    wxUnusedVar(tickPos);
+#endif
+}
+
+void wxSlider::DoSetTickFreq(int freq)
+{
+#if GTK_CHECK_VERSION(2,16,0)
+    if ( wx_is_at_least_gtk2(16) )
+    {
+        m_tickFreq = freq;
+        gtk_scale_clear_marks(GTK_SCALE (m_scale));
+
+        for (int i = GetMin() + freq; i < GetMax(); i += freq)
+            SetTick(i);
+    }
+#else
+    wxUnusedVar(freq);
+#endif
+}
+
+int wxSlider::GetTickFreq() const
+{
+#if GTK_CHECK_VERSION(2,16,0)
+    return wx_is_at_least_gtk2(16) ? m_tickFreq : -1;
+#else
+    return -1;
+#endif
+}
+
 GdkWindow *wxSlider::GTKGetWindow(wxArrayGdkWindows& WXUNUSED(windows)) const
 {
 #ifdef __WXGTK3__