Allow turning on/off opacity selector in wxColourDialog (wxOSX)

This feature to show/hide alpha values and opacity selector (slider) is
already implemented under wxGTK and for generic wxColourDialog.
For the sake of backward compatibility, this feature is enabled here by
default (through the corresponding property of wxColourData).

docs/changes.txt

@@ -213,6 +213,7 @@ wxOSX:
 - Add a native implementation for clearing bitmap/window wxGraphicsContexts
 - wxiOS now needs a minimum of iOS 9 for deployment
 - Fix handling CTM in wxGraphicsContext::SeTransform and GetTransform().
+- Allow turning on/off opacity selector in wxColourDialog.
 
 Unix:
 

interface/wx/colourdata.h

@@ -46,6 +46,16 @@ public:
     */
     bool GetChooseFull() const;
 
+    /**
+        Indicates whether the colour dialog will display alpha values
+        and an opacity selector. It is meaningful under wxGTK, wxOSX
+        and with regards to generic colour dialog.
+
+        The default value is @false, except wxOSX where it is @true (for
+        the sake of backward compatibility).
+    */
+    bool GetChooseAlpha() const;
+
     /**
         Gets the current colour associated with the colour dialog.
 
@@ -72,6 +82,16 @@ public:
     */
     void SetChooseFull(bool flag);
 
+    /**
+        Tells the colour dialog to show alpha values and an opacity selector
+        (slider). Currently it has effect under wxGTK, wxOSX and for generic
+        colour dialog.
+
+        The default value is @false, except wxOSX where it is @true for
+        backward compatibility.
+    */
+    void SetChooseAlpha(bool flag);
+
     /**
         Sets the default colour for the colour dialog.
 

src/common/colourdata.cpp

@@ -25,7 +25,14 @@ wxIMPLEMENT_DYNAMIC_CLASS(wxColourData, wxObject);
 wxColourData::wxColourData()
 {
     m_chooseFull = false;
+#ifdef __WXOSX__
+    // Under OSX, legacy wxColourDialog had opacity selector
+    // (slider) always enabled, so for backward compatibilty
+    // we should tell the dialog to enable it by default.
+    m_chooseAlpha = true;
+#else
     m_chooseAlpha = false;
+#endif // __WXOSX__ / !__WXOSX__
     m_dataColour.Set(0,0,0);
     // m_custColours are wxNullColours initially
 }

src/osx/carbon/colordlgosx.mm

@@ -106,7 +106,7 @@ bool wxColourDialog::Create(wxWindow *parent, wxColourData *data)
     NSAutoreleasePool *thePool;
     thePool = [[NSAutoreleasePool alloc] init];
 
-    [[NSColorPanel sharedColorPanel] setShowsAlpha:YES];
+    [[NSColorPanel sharedColorPanel] setShowsAlpha:m_colourData.GetChooseAlpha() ? YES : NO];
     if(m_colourData.GetColour().IsOk())
         [[NSColorPanel sharedColorPanel] setColor:m_colourData.GetColour().OSXGetNSColor()];
     else