ui: remove ui.Ops parameters from layouts and path builder structs

Layouts and path builders are transient and need an ops list for
operation. However, instead of passing the ops list to every method,
pass the list in an init method and store it for subsequent methods.

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

ui/layout/list.go

@@ -24,6 +24,7 @@ type List struct {
 	// The distance scrolled since last call to Init.
 	Distance int
 
+	ops       *ui.Ops
 	scroll    gesture.Scroll
 	scrollDir int
 
@@ -46,7 +47,8 @@ const (
 	iterateBackward
 )
 
-func (l *List) Init(cs Constraints, len int) {
+func (l *List) Init(ops *ui.Ops, cs Constraints, len int) {
+	l.ops = ops
 	l.dir = iterateNone
 	l.maxSize = 0
 	l.children = l.children[:0]
@@ -55,6 +57,7 @@ func (l *List) Init(cs Constraints, len int) {
 	if l.first > len {
 		l.first = len
 	}
+	ops.Begin()
 }
 
 func (l *List) Dragging() bool {
@@ -69,19 +72,16 @@ func (l *List) Update(c *ui.Config, q pointer.Events) {
 	l.offset += d
 }
 
-func (l *List) Next(ops *ui.Ops) (int, Constraints, bool) {
+func (l *List) Next() (int, Constraints, bool) {
 	if l.dir != iterateNone {
 		panic("a previous Next was not finished with Elem")
 	}
 	i, ok := l.next()
 	var cs Constraints
 	if ok {
-		if len(l.children) == 0 {
-			ops.Begin()
-		}
 		cs = axisConstraints(l.Axis, Constraint{Max: ui.Inf}, l.crossConstraintChild(l.cs))
-		ops.Begin()
-		ui.OpLayer{}.Add(ops)
+		l.ops.Begin()
+		ui.OpLayer{}.Add(l.ops)
 	}
 	return i, cs, ok
 }
@@ -110,8 +110,8 @@ func (l *List) next() (int, bool) {
 	return 0, false
 }
 
-func (l *List) End(ops *ui.Ops, dims Dimens) {
-	block := ops.End()
+func (l *List) End(dims Dimens) {
+	block := l.ops.End()
 	child := scrollChild{dims.Size, block}
 	switch l.dir {
 	case iterateForward:
@@ -130,7 +130,7 @@ func (l *List) End(ops *ui.Ops, dims Dimens) {
 	l.dir = iterateNone
 }
 
-func (l *List) Layout(ops *ui.Ops) Dimens {
+func (l *List) Layout() Dimens {
 	mainc := axisMainConstraint(l.Axis, l.cs)
 	for len(l.children) > 0 {
 		sz := l.children[0].size
@@ -155,6 +155,7 @@ func (l *List) Layout(ops *ui.Ops) Dimens {
 			break
 		}
 	}
+	ops := l.ops
 	pos := -l.offset
 	for _, child := range l.children {
 		sz := child.size
@@ -192,12 +193,10 @@ func (l *List) Layout(ops *ui.Ops) Dimens {
 		l.scroll.Stop()
 	}
 	dims := axisPoint(l.Axis, mainc.Constrain(pos), maxCross)
-	if len(l.children) > 0 {
-		block := ops.End()
-		pointer.AreaRect(dims).Add(ops)
-		l.scroll.Add(ops)
-		block.Add(ops)
-	}
+	block := ops.End()
+	pointer.AreaRect(dims).Add(ops)
+	l.scroll.Add(ops)
+	block.Add(ops)
 	return Dimens{Size: dims}
 }