system

type CommandEvent struct {
	Type CommandType
	// Cancel suppress the default action of the command.
	Cancel bool
}

type CommandType uint8

type DestroyEvent struct {
	// Err is nil for normal window closures. If a
	// window is prematurely closed, Err is the cause.
	Err error
}

type FrameEvent struct {
	// Now is the current animation. Use Now instead of time.Now to
	// synchronize animation and to avoid the time.Now call overhead.
	Now time.Time
	// Metric converts device independent dp and sp to device pixels.
	Metric unit.Metric
	// Size is the dimensions of the window.
	Size image.Point
	// Insets is the insets to apply.
	Insets Insets
	// Frame is the callback to supply the list of
	// operations to complete the FrameEvent.
	//
	// Note that the operation list and the operations themselves
	// may not be mutated until another FrameEvent is received from
	// the same event source.
	// That means that calls to frame.Reset and changes to referenced
	// data such as ImageOp backing images should happen between
	// receiving a FrameEvent and calling Frame.
	//
	// Example:
	//
	//  var w *app.Window
	//  var frame *op.Ops
	//  for e := range w.Events() {
	//      if e, ok := e.(system.FrameEvent); ok {
	//          // Call frame.Reset and manipulate images for ImageOps
	//          // here.
	//          e.Frame(frame)
	//      }
	//  }
	Frame func(frame *op.Ops)
	// Queue supplies the events for event handlers.
	Queue event.Queue
}

type Insets struct {
	Top, Bottom, Left, Right unit.Value
}

type Stage uint8

type StageEvent struct {
	Stage Stage
}