layout,gesture: add option to handle vertical scroll on horizontal list

Previously, it was impossible to scroll a Axis == Horizontal using
ordinary mouse-wheel. Now, it's possible to set ScrollAnyAxis == True,
which combine scrolling from any direction. That makes possible
to scroll Horizontal lists with vertical mouse-wheel.

By default this option is false, keeping the old behaviour.

Signed-off-by: inkeliz <inkeliz@inkeliz.com>

layout/list.go

@@ -29,6 +29,8 @@ type List struct {
 	ScrollToEnd bool
 	// Alignment is the cross axis alignment of list elements.
 	Alignment Alignment
+	// ScrollAnyAxis allows any scroll axis to scroll the list, not just the main axis.
+	ScrollAnyAxis bool
 
 	cs          Constraints
 	scroll      gesture.Scroll
@@ -159,12 +161,19 @@ func (l *List) update(gtx Context) {
 			max = 0
 		}
 	}
+
 	xrange := pointer.ScrollRange{Min: min, Max: max}
 	yrange := pointer.ScrollRange{}
-	if l.Axis == Vertical {
+
+	axis := gesture.Axis(l.Axis)
+	if l.ScrollAnyAxis {
+		axis = gesture.Both
+		yrange = xrange
+	} else if l.Axis == Vertical {
 		xrange, yrange = yrange, xrange
 	}
-	d := l.scroll.Update(gtx.Metric, gtx.Source, gtx.Now, gesture.Axis(l.Axis), xrange, yrange)
+	d := l.scroll.Update(gtx.Metric, gtx.Source, gtx.Now, axis, xrange, yrange)
+
 	l.scrollDelta = d
 	l.Position.Offset += d
 }