ui: move macro recording from Ops to MacroOp

Move the Record and Stop methods from Ops to MacroOp itself.

Before this change, Ops.Stop stopped the recording of the most
recent macro, which could be a different macro than intended.
After this change, there is no such confusion.

As a bonus, the Ops API becomes less cluttered.

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

ui/layout/list.go

@@ -27,6 +27,8 @@ type List struct {
 	// The distance scrolled since last call to Init.
 	Distance int
 
+	macro     ui.MacroOp
+	child     ui.MacroOp
 	ops       *ui.Ops
 	scroll    gesture.Scroll
 	scrollDir int
@@ -70,7 +72,7 @@ func (l *List) Init(ops *ui.Ops, cs Constraints, len int) {
 	if l.first > len {
 		l.first = len
 	}
-	ops.Record()
+	l.macro.Record(ops)
 	l.Next()
 }
 
@@ -103,7 +105,7 @@ func (l *List) Next() {
 		i = l.len - 1 - i
 	}
 	l.index = i
-	l.ops.Record()
+	l.child.Record(l.ops)
 }
 
 // Index is the current element index.
@@ -146,8 +148,8 @@ func (l *List) next() (int, bool) {
 
 // Elem completes an element.
 func (l *List) Elem(dims Dimens) {
-	macro := l.ops.Stop()
-	child := scrollChild{dims.Size, macro}
+	l.child.Stop()
+	child := scrollChild{dims.Size, l.child}
 	switch l.dir {
 	case iterateForward:
 		mainSize := axisMain(l.Axis, child.size)
@@ -237,9 +239,9 @@ func (l *List) Layout() Dimens {
 		l.scroll.Stop()
 	}
 	dims := axisPoint(l.Axis, mainc.Constrain(pos), maxCross)
-	macro := ops.Stop()
+	l.macro.Stop()
 	pointer.RectAreaOp{Size: dims}.Add(ops)
 	l.scroll.Add(ops)
-	macro.Add(ops)
+	l.macro.Add(ops)
 	return Dimens{Size: dims}
 }