io/pointer,io/router: replace AreaOp with clip.Op

Pointer hit areas and paint clip areas are separate concepts, but
similar enough to warrant merging. This change replaces pointer hit
areas with clip areas, so Gio is left with just one area concept (in
package op/clip).

The reason for separating the concepts in the original Gio release was
because of my being unsure general path/stroke hit areas would ever be
implemented, let alone efficient.

This change represents a change of mind, in the sense that it's better
to have an incomplete API than two separate area concepts.

Leave the deprecated pointer.Rect, pointer.Ellipse for temporary
backwards compatibility.

This is an API change. Most existing programs should continue to build
with this change, but may have to adjust to having all clip.Ops participate
in InputOp hit areas.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/list.go

@@ -92,19 +92,19 @@ func (s *Scrollbar) Layout(gtx layout.Context, axis layout.Axis, viewportStart,
 }
 
 // AddTrack configures the track click listener for the scrollbar to use
-// the most recently added pointer.AreaOp.
+// the current clip area.
 func (s *Scrollbar) AddTrack(ops *op.Ops) {
 	s.track.Add(ops)
 }
 
 // AddIndicator configures the indicator click listener for the scrollbar to use
-// the most recently added pointer.AreaOp.
+// the current clip area.
 func (s *Scrollbar) AddIndicator(ops *op.Ops) {
 	s.indicator.Add(ops)
 }
 
 // AddDrag configures the drag listener for the scrollbar to use
-// the most recently added pointer.AreaOp.
+// the current clip area.
 func (s *Scrollbar) AddDrag(ops *op.Ops) {
 	s.drag.Add(ops)
 }