layout: default List scroll bounds to infinity

Before, List would only report the remaining scrollable area of the visible
children when positioned close to either end. Now, List always report infinite
scroll bounds *unless* it is positioned at an extremum.

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

layout/list.go

@@ -302,17 +302,19 @@ func (l *List) layout(ops *op.Ops, macro op.MacroOp) Dimensions {
 	call := macro.Stop()
 	defer clip.Rect(image.Rectangle{Max: dims}).Push(ops).Pop()
 
-	var min, max int
-	if o := l.Position.Offset; o > 0 {
+	min, max := int(-inf), int(inf)
+	if l.Position.First == 0 {
 		// Use the size of the invisible part as scroll boundary.
-		min = -o
-	} else if l.Position.First > 0 {
-		min = -inf
+		min = -l.Position.Offset
+		if min > 0 {
+			min = 0
+		}
 	}
-	if o := l.Position.OffsetLast; o < 0 {
-		max = -o
-	} else if l.Position.First+l.Position.Count < l.len {
-		max = inf
+	if l.Position.First+l.Position.Count == l.len {
+		max = -l.Position.OffsetLast
+		if max < 0 {
+			max = 0
+		}
 	}
 	scrollRange := image.Rectangle{
 		Min: l.Axis.Convert(image.Pt(min, 0)),