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/flex.go

@@ -22,7 +22,6 @@ type Flex struct {
 
 	ctx       *Context
 	macro     ui.MacroOp
-	ops       *ui.Ops
 	mode      flexMode
 	size      int
 	rigidSize int
@@ -69,13 +68,12 @@ const (
 )
 
 // Init must be called before Rigid or Flexible.
-func (f *Flex) Init(ops *ui.Ops, ctx *Context) *Flex {
+func (f *Flex) Init(c *Context) *Flex {
 	if f.mode > modeBegun {
 		panic("must End the current child before calling Init again")
 	}
 	f.mode = modeBegun
-	f.ops = ops
-	f.ctx = ctx
+	f.ctx = c
 	f.size = 0
 	f.rigidSize = 0
 	f.maxCross = 0
@@ -91,7 +89,7 @@ func (f *Flex) begin(mode flexMode) {
 		panic("must End before adding a child")
 	}
 	f.mode = mode
-	f.macro.Record(f.ops)
+	f.macro.Record(f.ctx.Ops)
 }
 
 // Rigid lays out a widget with the main axis constrained to the range
@@ -192,9 +190,9 @@ func (f *Flex) Layout(children ...FlexChild) {
 			}
 		}
 		var stack ui.StackOp
-		stack.Push(f.ops)
-		ui.TransformOp{}.Offset(toPointF(axisPoint(f.Axis, mainSize, cross))).Add(f.ops)
-		child.macro.Add(f.ops)
+		stack.Push(f.ctx.Ops)
+		ui.TransformOp{}.Offset(toPointF(axisPoint(f.Axis, mainSize, cross))).Add(f.ctx.Ops)
+		child.macro.Add(f.ctx.Ops)
 		stack.Pop()
 		mainSize += axisMain(f.Axis, dims.Size)
 		if i < len(children)-1 {