How to use Fyne just to render the GUI to an image ?

[kedare]

Hello :)

I am currently working on a project using eink display like this one

I first started drawing raw image but as the layout gets more complex it's getting really painful so I was thinking to use fyne to render the GUI an an image.

I can make a screenshot responding to a button for example like this

func BuildWindow(app fyne.App) fyne.Window {
	w := app.NewWindow("Dashink")
	w.Resize(fyne.NewSize(WIDTH, HEIGHT))
	w.SetFixedSize(true)

	hello := widget.NewLabel("Hello Fyne!")
	w.SetContent(container.NewVBox(
		hello,
		widget.NewButton("Hi!", func() {
			hello.SetText("Welcome :)")
			output.CaptureWindowToFile(w, "screenshot.png")
			w.Close()
		}),
	))

	return w
}

func CaptureWindowToFile(w fyne.Window, fileName string) {
	log.Println("Starting saving screenshot")
	// Capture the current window's canvas content
	img := w.Canvas().Capture()

	// Create a file to save the image
	f, err := os.Create(fileName)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()

	// Encode the image as a PNG and write it to the file
	err = png.Encode(f, img)
	if err != nil {
		log.Fatal(err)
	}
	log.Println("Screenshot saved to", fileName)
}

But then now I am trying to make it completely headless like this

func main() {
	log.Println("Starting")
	app := app.New()
	window := gui.BuildWindow(app)
	log.Println("Showing GUI")
	window.ShowAndRun()
	output.CaptureWindowToFile(window, "screenshot.png")
}

but the window.ShowAndRun being blocking, the code never reach the screenshot part.

How can I achieve this ? Is there a way to define something like a OnShow event on the Window to run this code of code like I could do to respond tu a button click ?

Thanks

[andydotxyz]

To answer the question most directly you are looking for the App.Lifecycle() api which will run a callback when the app is foregrounded (window is completely shown).

Alternatively you can run your capture code from a goroutine that is started before you run the app.

However running the app headless using the default driver will still use the main display to show the window - is that what you want?

There is also the software renderer like we use in unit testing which does not use the screen at all, and does not have the event loop to work around. Of course the trade-off is that you would have to handle events but I expect you'll have to do that anyway with your eink device.

[kedare]

Thanks for the answer.

So far I am using xvfb-run to run the app as it needs a display available but indeed if there is a way to do without just using Go I would love to 😄
Would you have a reference I can look into to use it ? Would it work outside of unit testing ?

So far I tried with a goroutine and it works but I guess it would be more cleaner via the application lifecycle (to ensure everything has been loaded already for example instead of waiting an arbitrary sleep time)

[andydotxyz]

Would you have a reference I can look into to use it ?

Maybe https://github.com/fynelabs/snowflake/blob/ed3b7906ebdcfa5d258e913a88ec3309346793f9/snowflake.go#L143

In general the driver/software package provides a few great items - the snippet above pre-dates that but it's the same idea.

Would it work outside of unit testing ?

Yes