NSScroller: define scroller styles

As of macOS 10.7, scrollers gained two types: Legacy and Overlay. Here,
we define these styles as well as a method to determine which is the
"default" style to be used.

Headers/AppKit/NSScroller.h

@@ -37,6 +37,21 @@
 
 @class NSEvent;
 
+#if OS_API_VERSION(MAC_OS_X_VERSION_10_7, GS_API_LATEST)
+enum {
+  NSScrollerStyleLegacy = 0,
+  NSScrollerStyleOverlay = 1
+};
+typedef NSInteger NSScrollerStyle;
+
+enum {
+  NSScrollerKnobStyleDefault = 0,
+  NSScrollerKnobStyleDark = 1,
+  NSScrollerKnobStyleLight = 2
+};
+typedef NSInteger NSScrollerKnobStyle;
+#endif
+
 enum _NSScrollArrowPosition {
 #if OS_API_VERSION(MAC_OS_X_VERSION_10_1, GS_API_LATEST)
   NSScrollerArrowsDefaultSetting = 0,
@@ -90,6 +105,10 @@ typedef NSUInteger NSScrollerArrow;
   } _scFlags;
 }
 
+#if OS_API_VERSION(MAC_OS_X_VERSION_10_7, GS_API_LATEST)
++ (NSScrollerStyle)preferredScrollerStyle;
+#endif
+
 //
 // Laying out the NSScroller 
 //
@@ -144,4 +163,6 @@ typedef NSUInteger NSScrollerArrow;
 
 @end
 
+APPKIT_EXPORT NSString *NSPreferredScrollerStyleDidChangeNotification;
+
 #endif // _GNUstep_H_NSScroller

Source/NSScroller.m

@@ -49,6 +49,9 @@
 
 #import "GNUstepGUI/GSTheme.h"
 
+NSString *NSPreferredScrollerStyleDidChangeNotification =
+  @"NSPreferredScrollerStyleDidChangeNotification";
+
 /**<p>TODO Description</p>
  */
 @implementation NSScroller
@@ -130,6 +133,12 @@ static float	buttonsOffset = 1.0; // buttonsWidth = sw - 2*buttonsOffset
   return scrollerWidth;
 }
 
++ (NSScrollerStyle)preferredScrollerStyle
+{
+  // FIXME: a theme should define this?
+  return NSScrollerStyleLegacy;
+}
+
 - (BOOL) isFlipped
 {
   return YES;