Understanding CanvasObject and the canvas package
The CanvasObject definition is just a Go interface that describes an element that can be positioned, sized, and added to a Fyne canvas. The type does not contain any information about how to draw—this information is provided by concrete types within the canvas package. These types define well-understood graphical primitives, such as Text and Line.
Before learning how to use these elements, we shall see how they look in the Fyne demo app.
Canvas demo
Before we look at how to write code that will display shapes in our window, we should look at a demo of these features in action. Using the built-in Fyne demo application, we can see what the canvas package supports. If you have not already done so, you can install and run the demo application using the following commands:
$ go get fyne.io/fyne/v2/cmd/fyne_demo $ ~/go/bin/fyne_demo
While running the demo, tap on the Canvas item on the left navigation panel. You should...