Programming Python, 3rd Edition

Canvas

When it comes to graphics, the Tkinter Canvas widget is the most free-form device in the library. It’s a place to draw shapes, move objects dynamically, and place other kinds of widgets. The canvas is based on a structured graphic object model: everything drawn on a canvas can be processed as an object. You can get down to the pixel-by-pixel level in a canvas, but you can also deal in terms of larger objects such as shapes, photos, and embedded widgets. And the canvas is powerful enough to support everything from simple paint programs to full-scale visualization and animation.

Basic Canvas Operations

Canvases are ubiquitous in much nontrivial GUI work, and we’ll see larger canvas examples show up later in this book under the names PyDraw, PyView, PyClock, and PyTree. For now, let’s jump right into an example that illustrates the basics. Example 10-13 runs most of the major canvas drawing methods.

Example 10-13. PP3E\Gui\Tour\canvas1.py

# demo all basic canvas interfaces from Tkinter import * canvas = Canvas(width=300, height=300, bg='white') # 0,0 is top left corner canvas.pack(expand=YES, fill=BOTH) # increases down, right canvas.create_line(100, 100, 200, 200) # fromX, fromY, toX, toY canvas.create_line(100, 200, 200, 300) # draw shapes for i in range(1, 20, 2): canvas.create_line(0, i, 50, i) canvas.create_oval(10, 10, 200, 200, width=2, fill='blue') canvas.create_arc(200, 200, 300, 100) canvas.create_rectangle(200, 200, 300, 300, width=5, fill='red') canvas.create_line(0, ...