Grab GTK default colors for infobar

This implements the wxWidgets fix for KiCad.  We can't wait for distros
to update their wx libs so until then, we'll roll our own.

Nicely, this also implements the MacOS setting that was an ifdef
previously

Fixes https://gitlab.com/kicad/code/kicad/-/issues/19506

common/widgets/wx_infobar.cpp

@@ -58,12 +58,11 @@ WX_INFOBAR::WX_INFOBAR( wxWindow* aParent, wxAuiManager* aMgr, wxWindowID aWinid
 {
     m_showTimer = new wxTimer( this, ID_CLOSE_INFOBAR );
 
+    wxColour fg, bg;
+    KIPLATFORM::UI::GetInfoBarColours( bg, fg );
+    SetBackgroundColour( bg );
+    SetForegroundColour( fg );
 #ifdef __WXMAC__
-    // wxWidgets hard-codes wxSYS_COLOUR_INFOBK to { 0xFF, 0xFF, 0xD3 } on Mac.
-    if( KIPLATFORM::UI::IsDarkTheme() )
-        SetBackgroundColour( wxColour( 28, 27, 20 ) );
-    else
-        SetBackgroundColour( wxColour( 255, 249, 189 ) );
 
     // Infobar is broken on Mac without the effects
     SetShowHideEffects( wxSHOW_EFFECT_ROLL_TO_BOTTOM, wxSHOW_EFFECT_ROLL_TO_TOP );

libs/kiplatform/include/kiplatform/ui.h

@@ -119,6 +119,11 @@ namespace KIPLATFORM
          */
         double GetContentScaleFactor( const wxWindow* aWindow );
 
+        /**
+         * Return the background and foreground colors for info bars in the current scheme
+         */
+        void GetInfoBarColours( wxColour& aFGColour, wxColour& aBGColour );
+
         /**
          * Tries to determine the size of the viewport of a scrollable widget (wxDataViewCtrl, wxGrid)
          * that won't be obscured by scrollbars.

libs/kiplatform/port/wxgtk/ui.cpp

@@ -64,6 +64,45 @@ wxColour KIPLATFORM::UI::GetDialogBGColour()
 }
 
 
+void KIPLATFORM::UI::GetInfoBarColours( wxColour& aBgColour, wxColour& aFgColour )
+{
+    // The GTK3.24 way of getting the colours is to use the style context
+    // Earlier GTKs should be able to use the system settings
+#if( GTK_CHECK_VERSION( 3, 24, 0 ) )
+    GdkRGBA* rgba;
+    GtkWidgetPath*   path = gtk_widget_path_new();
+    GtkStyleContext* sc = gtk_style_context_new();
+    gtk_widget_path_append_type( path, GTK_TYPE_WINDOW );
+    gtk_widget_path_iter_set_object_name( path, -1, "infobar" );
+    gtk_widget_path_iter_add_class( path, -1, "background" );
+    gtk_widget_path_iter_add_class( path, -1, "info" );
+    gtk_widget_path_append_type( path, G_TYPE_NONE );
+    gtk_widget_path_iter_set_object_name( path, -1, "revealer" );
+    gtk_widget_path_append_type( path, G_TYPE_NONE );
+    gtk_widget_path_iter_set_object_name( path, -1, "box" );
+
+    gtk_style_context_set_path( sc, path );
+    gtk_style_context_set_state( sc, GTK_STATE_FLAG_NORMAL );
+
+    gtk_style_context_get( sc, GTK_STATE_FLAG_NORMAL, "background-color", &rgba, NULL );
+    aBgColour = wxColour(*rgba);
+    gdk_rgba_free(rgba);
+
+    gtk_style_context_get( sc, GTK_STATE_FLAG_NORMAL, "color", &rgba, NULL );
+    aFgColour = wxColour(*rgba);
+    gdk_rgba_free(rgba);
+
+    gtk_widget_path_free( path );
+    g_object_unref( sc );
+
+#else
+    aBgColour = wxSystemSettings::GetColour( wxSYS_COLOUR_INFOBK );
+    aFgColour = wxSystemSettings::GetColour( wxSYS_COLOUR_INFOTEXT );
+#endif
+
+}
+
+
 void KIPLATFORM::UI::ForceFocus( wxWindow* aWindow )
 {
     aWindow->SetFocus();

libs/kiplatform/port/wxmsw/ui.cpp

@@ -73,6 +73,13 @@ wxColour KIPLATFORM::UI::GetDialogBGColour()
 }
 
 
+wxColour KIPLATFORM::UI::GetInfoBarColours( wxColour& aFGColour, wxColour& aBGColour )
+{
+    aBGColour = wxSystemSettings::GetColour( wxSYS_COLOUR_INFOBK );
+    aFGColour = wxSystemSettings::GetColour( wxSYS_COLOUR_INFOTEXT );
+}
+
+
 void KIPLATFORM::UI::ForceFocus( wxWindow* aWindow )
 {
     aWindow->SetFocus();

libs/kiplatform/port/wxosx/ui.mm

@@ -62,6 +62,18 @@ wxColour KIPLATFORM::UI::GetDialogBGColour()
 }
 
 
+void KIPLATFORM::UI::GetInfoBarColours( wxColour& aFGColour, wxColour& aBGColour )
+{
+    aFGColour = wxSystemSettings::GetColour( wxSYS_COLOUR_INFOTEXT );
+
+    // wxWidgets hard-codes wxSYS_COLOUR_INFOBK to { 0xFF, 0xFF, 0xD3 } on Mac.
+    if( KIPLATFORM::UI::IsDarkTheme() )
+        aBGColour = wxColour( 28, 27, 20 );
+    else
+        aBGColour = wxColour( 255, 249, 189 );
+}
+
+
 void KIPLATFORM::UI::ForceFocus( wxWindow* aWindow )
 {
     // On OSX we need to forcefully give the focus to the window