ui/layout: add common state to Context

Almost every layout and widget need the ui.Config for its environment,
an ui.Ops to store operations. Stateful widgets need an input.Queue
for events.

Add all these common objects to Context, greatly simplifying the
function signatures for Gio programs.

Fixes gio#33

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

ui/layout/stack.go

@@ -16,7 +16,6 @@ type Stack struct {
 	Alignment Direction
 
 	macro       ui.MacroOp
-	ops         *ui.Ops
 	constrained bool
 	ctx         *Context
 	maxSZ       image.Point
@@ -30,9 +29,8 @@ type StackChild struct {
 }
 
 // Init a stack before calling Rigid or Expand.
-func (s *Stack) Init(ops *ui.Ops, ctx *Context) *Stack {
-	s.ops = ops
-	s.ctx = ctx
+func (s *Stack) Init(c *Context) *Stack {
+	s.ctx = c
 	s.constrained = true
 	s.maxSZ = image.Point{}
 	s.baseline = 0
@@ -43,7 +41,7 @@ func (s *Stack) begin() {
 	if !s.constrained {
 		panic("must Init before adding a child")
 	}
-	s.macro.Record(s.ops)
+	s.macro.Record(s.ctx.Ops)
 }
 
 // Rigid lays out a widget with the same constraints that were
@@ -102,9 +100,9 @@ func (s *Stack) Layout(children ...StackChild) {
 			p.Y = s.maxSZ.Y - sz.Y
 		}
 		var stack ui.StackOp
-		stack.Push(s.ops)
-		ui.TransformOp{}.Offset(toPointF(p)).Add(s.ops)
-		ch.macro.Add(s.ops)
+		stack.Push(s.ctx.Ops)
+		ui.TransformOp{}.Offset(toPointF(p)).Add(s.ctx.Ops)
+		ch.macro.Add(s.ctx.Ops)
 		stack.Pop()
 	}
 	b := s.baseline