Canvas

A canvas widget manages a 2D collection of graphical objects — lines, circles, text, images, other widgets, and more. Tk's canvas is an incredibly powerful and flexible widget and truly one of Tk's highlights. It is suitable for a wide range of uses, including drawing or diagramming, CAD tools, displaying or monitoring simulations or actual equipment, and building more complex widgets out of simpler ones.

Note: Canvas widgets are part of the classic Tk widgets, not the themed Tk widgets.

Canvas widgets

Canvas widgets are created using the canvas command:

#![allow(unused)]
fn main() {
parent.add_canvas( "canvas" -width(500) -height(400) -background("gray75") )?;
}

You'll often provide a width and height, either in pixels or any of the other standard distance units. As always, you can ask the geometry manager to expand it to fill the available space in the window. You might provide a default background color for the canvas, specifying colors as you learned about in the last chapter. Canvas widgets also support other appearance options like relief and borderwidth that we've used before.

Canvas widgets have a tremendous number of features, and we won't cover everything here. Instead, we'll start with a simple example, a freehand sketching tool, and incrementally add new pieces, each showing another feature of canvas widgets.