Fl_Roller can now be controlled via the mouse wheel (STR #3120).

CHANGES.txt

@@ -102,6 +102,7 @@ Changes in FLTK 1.4.0					Released: ??? ?? 2019
   Other Improvements
 
   - (add new items here)
+  - Fl_Roller can now be controlled via the mouse wheel (STR #3120).
   - Tooltips hide by themselves after 12 seconds (STR #2584).
   - Added widget visibility indicator to Fluid (STR #2669).
   - Added Fl_Input_::append() method (STR #2953).

FL/Fl_Roller.H

@@ -29,6 +29,11 @@
 /**
   The Fl_Roller widget is a "dolly" control commonly used to
   move 3D objects.
+
+  The Roller can be controlled by clicking an ddragging the mouse, by the
+  corresponding arrow keys when the roller has the keyboard focus, or by the
+  mousewheels when the mouse pointer is positioned over the roller widget.
+ 
   <P ALIGN=CENTER>\image html Fl_Roller.png 
   \image latex Fl_Roller.png "Fl_Roller" width=4cm
 */

src/Fl_Roller.cxx

@@ -41,6 +41,21 @@ int Fl_Roller::handle(int event) {
     case FL_RELEASE:
       handle_release();
       return 1;
+    case FL_MOUSEWHEEL :
+      if (Fl::belowmouse()==this) {
+        if (horizontal()) {
+          if (Fl::e_dx!=0) {
+            handle_drag(clamp(round(increment(value(),-Fl::e_dx))));
+          }
+        } else {
+          if (Fl::e_dy!=0) {
+            handle_drag(clamp(round(increment(value(),-Fl::e_dy))));
+          }
+        }
+        return 1;
+      } else {
+        return 0;
+      }
     case FL_KEYBOARD :
       switch (Fl::event_key()) {
         case FL_Up: