canvas.rst

Canvas

macOS	GTK+	Windows	iOS	Android	Django

The canvas is used for creating a blank widget that you can draw on.

Usage

Simple usage to draw a black circle on the screen using the arc drawing object:

import toga
canvas = toga.Canvas(style=Pack(flex=1))
box = toga.Box(children=[canvas])
with canvas.fill() as fill:
    fill.arc(50, 50, 15)

More advanced usage for something like a vector drawing app where you would want to modify the parameters of the drawing objects. Here we draw a black circle and black rectangle. We then change the size of the circle, move the rectangle, and finally delete the rectangle.

import toga
canvas = toga.Canvas(style=Pack(flex=1))
box = toga.Box(children=[canvas])
with canvas.fill() as fill:
    arc1 = fill.arc(x=50, y=50, radius=15)
    rect1 = fill.rect(x=50, y=50, width=15, height=15)

arc1.x, arc1.y, arc1.radius = (25, 25, 5)
rect1.x = 75
fill.remove(rect1)

Use of drawing contexts, for example with a platformer game. Here you would want to modify the x/y coordinate of a drawing context that draws each character on the canvas. First, we create a hero context. Next, we create a black circle and a black outlined rectangle for the hero's body. Finally, we move the hero by 10 on the x-axis.

import toga
canvas = toga.Canvas(style=Pack(flex=1))
box = toga.Box(children=[canvas])
with canvas.context() as hero:
    with hero.fill() as body:
        body.arc(50, 50, 15)
    with hero.stroke() as outline:
        outline.rect(50, 50, 15, 15)

hero.translate(10, 0)

Reference

Main Interface

toga.widgets.canvas.Canvas

Lower-Level Classes

toga.widgets.canvas