func main() {
	app.Main(func(a app.App) {
		var glctx gl.Context
		var sz size.Event 
		tick := time.NewTicker(15 * time.Millisecond)
		events := a.Events()
		for {
			select {
			case e := <-events:
				switch e := a.Filter(e).(type) {
					case lifecycle.Event:
						switch e.Crosses(lifecycle.StageVisible) {
						case lifecycle.CrossOn:
							glctx, _ = e.DrawContext.(gl.Context)
							onStart(glctx)
						case lifecycle.CrossOff:
							onStop(glctx)
							glctx = nil
						}
					case size.Event:
						sz = e
						touchX = float32(sz.WidthPx / 2)
						touchY = float32(sz.HeightPx / 2)
					case paint.Event:
						// nothing to do here
					case touch.Event:
						touchX = e.X
						touchY = e.Y
					} 
			case <-tick:
				if glctx != nil {
					onPaint(glctx, sz)
					a.Publish()
				}
			}
		}
	})
}