Let's get started with writing a simple hello world window, as in the previous chapters. This code is a little more complicated than in previous examples due to the low-level nature of the toolkit at this time. As well as defining the window, label, and button, we will need to set up a background layer and measure the minimum size for the containing window:

package main

import (
   "golang.org/x/exp/shiny/driver"
   "golang.org/x/exp/shiny/screen"
   "golang.org/x/exp/shiny/widget"
   "golang.org/x/exp/shiny/widget/theme"

   "log"
)

func main() {
   driver.Main(func(s screen.Screen) {
      label := widget.NewLabel("Hello World!")
      button := newButton("Quit",
         func() {
            log.Println("To quit close this window")
         })

      w := widget.NewFlow(widget.AxisVertical, label, button)
      sheet := widget.NewSheet(widget.NewUniform(theme.Neutral, w))

      w.Measure(theme.Default, 0, 0)
      if err := widget.RunWindow(s, sheet, &widget.RunWindowOptions{
         NewWindowOptions: screen.NewWindowOptions{
            Title: "Hello",
            Width: w.MeasuredSize.X,
            Height: w.MeasuredSize.Y,
         },
      }); err != nil {
         log.Fatal(err)
      }
   })
}

In the preceding code, you can see the flow layout (widget.NewFlow()), a background layer (widget.NewSheet()), and the measurement initialization (w.Measure()). With Shiny, widget.Sheet is required underneath any widgets so they can paint correctly. On a simple application, a single sheet should be sufficient, but on a more complex user interface where items move independently (that is, scrolling), additional sheets will probably be required.