Add wxActivityIndicator control.

This is a simple animated control indicating some program activity.

Provide native GTK+ (for > 2.20) and OS X implementations as well as a generic
one used under MSW.

Update the sample and the documentation.

src/gtk/activityindicator.cpp

@@ -0,0 +1,168 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        src/gtk/activityindicator.cpp
+// Purpose:     wxActivityIndicator implementation for wxGTK.
+// Author:      Vadim Zeitlin
+// Created:     2015-03-05
+// Copyright:   (c) 2015 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+// ============================================================================
+// declarations
+// ============================================================================
+
+// ----------------------------------------------------------------------------
+// headers
+// ----------------------------------------------------------------------------
+
+// for compilers that support precompilation, includes "wx.h".
+#include "wx/wxprec.h"
+
+#ifdef __BORLANDC__
+    #pragma hdrstop
+#endif
+
+#if wxUSE_ACTIVITYINDICATOR && defined(__WXGTK220__)
+
+#include "wx/activityindicator.h"
+
+#include "wx/math.h"
+
+#include <gtk/gtk.h>
+
+// Macro return the specified expression only if GTK+ run time version is less
+// than 2.20 and compiling it only if it is less than 3.0 (which is why this
+// has to be a macro and not a function).
+#if defined(__WXGTK220__) && !defined(__WXGTK3__)
+    #define RETURN_IF_NO_GTK_SPINNER(expr) \
+        if ( gtk_check_version(2, 20, 0) != 0 ) { return expr; }
+#else
+    #define RETURN_IF_NO_GTK_SPINNER(expr)
+#endif
+
+// ============================================================================
+// implementation
+// ============================================================================
+
+wxIMPLEMENT_DYNAMIC_CLASS(wxActivityIndicator, wxControl);
+
+bool
+wxActivityIndicator::Create(wxWindow* parent,
+                            wxWindowID winid,
+                            const wxPoint& pos,
+                            const wxSize& size,
+                            long style,
+                            const wxString& name)
+{
+    RETURN_IF_NO_GTK_SPINNER(
+        wxActivityIndicatorGeneric::Create(parent, winid, pos, size, style, name)
+    )
+
+    if ( !PreCreation(parent, pos, size) ||
+             !CreateBase(parent, winid, pos, size, style, name) )
+        return false;
+
+    m_widget = gtk_spinner_new();
+    g_object_ref(m_widget);
+
+    m_parent->DoAddChild(this);
+
+    PostCreation(size);
+
+    return true;
+}
+
+void wxActivityIndicator::Start()
+{
+    RETURN_IF_NO_GTK_SPINNER( wxActivityIndicatorGeneric::Start() )
+
+    wxCHECK_RET( m_widget, wxS("Must be created first") );
+
+    gtk_spinner_start(GTK_SPINNER(m_widget));
+}
+
+void wxActivityIndicator::Stop()
+{
+    RETURN_IF_NO_GTK_SPINNER( wxActivityIndicatorGeneric::Stop() )
+
+    wxCHECK_RET( m_widget, wxS("Must be created first") );
+
+    gtk_spinner_stop(GTK_SPINNER(m_widget));
+}
+
+bool wxActivityIndicator::IsRunning() const
+{
+    RETURN_IF_NO_GTK_SPINNER( wxActivityIndicatorGeneric::IsRunning() )
+
+    if ( !m_widget )
+        return false;
+
+    gboolean b;
+    g_object_get(m_widget, "active", &b, NULL);
+
+    return b != 0;
+}
+
+wxSize wxActivityIndicator::DoGetBestClientSize() const
+{
+    RETURN_IF_NO_GTK_SPINNER( wxActivityIndicatorGeneric::DoGetBestClientSize() )
+
+    if ( !m_widget )
+        return wxDefaultSize;
+
+    gint w, h;
+
+#ifdef __WXGTK3__
+    // gtk_widget_get_preferred_size() seems to return the size based on the
+    // current size of the widget and also always returns 0 if it is hidden,
+    // so ask GtkSpinner for its preferred size directly instead of using it.
+    GtkWidgetClass* const wc = GTK_WIDGET_GET_CLASS(m_widget);
+
+    // We're not interested in the natural size (and it's the same as minimal
+    // one anyhow currently), but we still need a non-NULL pointer for it.
+    gint dummy;
+    wc->get_preferred_width(m_widget, &w, &dummy);
+    wc->get_preferred_height(m_widget, &h, &dummy);
+#else // GTK+ 2
+    // GTK+ 2 doesn't return any valid preferred size for this control, so we
+    // use the size of something roughly equivalent to it.
+    gtk_icon_size_lookup(GTK_ICON_SIZE_MENU, &w, &h);
+#endif // GTK+ 3/2
+
+    // Adjust for the window variant: note that the default size in GTK+ 3 is
+    // really small (12px until ~3.10, 16px since then), so we use this size as
+    // the small size and double it for the normal size.
+    double factor = 0.;
+    switch ( GetWindowVariant() )
+    {
+        case wxWINDOW_VARIANT_MAX:
+            wxFAIL_MSG(wxS("Invalid window variant"));
+            wxFALLTHROUGH;
+
+        case wxWINDOW_VARIANT_NORMAL:
+            factor = 2.;
+            break;
+
+        case wxWINDOW_VARIANT_SMALL:
+            factor = 1.;
+            break;
+
+        case wxWINDOW_VARIANT_MINI:
+            factor = 0.75;
+            break;
+
+        case wxWINDOW_VARIANT_LARGE:
+            // GTK+ 3.11+ limits GtkSpinner size to twice its minimal size, so
+            // the effective factor here is actually just 2, i.e. the same as
+            // for the normal size, but use something larger just in case GTK+
+            // changes its mind again later.
+            factor = 2.5;
+            break;
+    }
+
+    wxASSERT_MSG( !wxIsSameDouble(factor, 0), wxS("Unknown window variant") );
+
+    return wxSize(wxRound(w*factor), wxRound(h*factor));
+}
+
+#endif // wxUSE_ACTIVITYINDICATOR