3. Turtle screen advanced

The code below shows some more useful methods for Turtle screens.

3.1. Screen background gif

See: https://docs.python.org/3/library/turtle.html#turtle.bgpic
Set a background image (gif file).
turtle.bgpic(picname=None)
picname - a string, name of a gif-file or “nopic”, or None; default None
Set background image or return the name of current background image.
If picname is a filename, set the corresponding image as background.
If picname is “nopic”, delete background image, if present. e.g s.bgpic(“nopic”)
If picname is None, return the filename of the current background image.
e.g print(s.bgpic(picname=None))
When s = turtle.Screen(), s.bgpic(...) can be used as below.
The code below sets the gackground image to a gif.
import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Mario")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing to go here

turtle.done()

Tasks

  1. Modify the code above to use a different gif of your own choice.

  2. Modify the code below to clear the gif while keeping the drawing.

import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing
t = turtle.Turtle()
t.speed(10)
t.color("blue", "red")
t.pensize(10)
t.pu()
t.goto(110, -290)
t.pd()
t.begin_fill()
t.circle(200)
t.end_fill()

turtle.done()

Modify the code below to clear the gif while keeping the drawing.

import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing
t = turtle.Turtle()
t.speed(10)
t.color("blue", "red")
t.pensize(10)
t.pu()
t.goto(110, -290)
t.pd()
t.begin_fill()
t.circle(200)
t.end_fill()

s.bgpic("nopic")

turtle.done()

3.2. Clear screen

See: https://docs.python.org/3/library/turtle.html#turtle.clearscreen
Clear the screen.
turtle.clearscreen()
Also turtle.clear()
Delete all drawings and all turtles from the TurtleScreen.
Reset the now empty Screen to its initial state: white background, no background image, no event bindings and tracing on.
When s = turtle.Screen(), s.clearscreen() can be used as below.
import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing
t = turtle.Turtle()
t.color("#285078", "#a0c8f0")
t.pensize(5)
t.fd(300)

s.clearscreen()

turtle.done()

Tasks

  1. Suggest a use case for s.clearscreen().

s.clearscreen() could be used to clear the screen between stages in a game that uses a different background and different turtles.

3.3. Reset screen

See: https://docs.python.org/3/library/turtle.html#turtle.resetscreen
Reset all turtles on the Screen.
turtle.resetscreen()
Also turtle.reset()
Reset all turtles on the Screen to their initial state, clearing their drawings.
When s = turtle.Screen(), s.resetscreen() can be used as below.
import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing
t = turtle.Turtle()
t.shapesize(10, 10, 12)
t.color("blue")
t.pensize(10)
t.penup(); t.setpos(-400, -230); t.pendown()
t.fd(800)

s.resetscreen()

# same turtle - new drawing
t.shapesize(5, 5, 6)
t.color("red")
t.pensize(10)
t.penup(); t.setpos(-400, -255); t.pendown()
t.fd(800)

turtle.done()

Tasks

  1. Adjust the code so that only one circle is drawn on the screen at any time.

import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing
t = turtle.Turtle()
t.speed(10)
t.color("blue", "red")
t.pensize(10)
t.begin_fill()
t.circle(120)
t.end_fill()


# same turtle - new drawing
t.color("green", "yellow")
t.pensize(5)
t.begin_fill()
t.circle(50)
t.end_fill()

turtle.done()

Adjust the code so that only one circle is drawn on the screen at any time.

import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=0, starty=0)

# turtle drawing
t = turtle.Turtle()
t.speed(10)
t.color("blue", "red")
t.pensize(10)
t.begin_fill()
t.circle(120)
t.end_fill()

s.resetscreen()

# same turtle - new drawing
t.color("green", "yellow")
t.pensize(5)
t.begin_fill()
t.circle(50)
t.end_fill()

turtle.done()

3.4. Reset screensize

See: https://docs.python.org/3/library/turtle.html#turtle.screensize
Reset the screensize.
turtle.screensize(canvwidth=None, canvheight=None, bg=None)
canvwidth - positive integer, new width of canvas in pixels; default None
canvheight - positive integer, new height of canvas in pixels; default None
bg - colorstring or color-tuple, new background color; default None
If no arguments are given, return current (canvaswidth, canvasheight).
Else, resize the canvas the turtles are drawing on without altering the drawings.
Scrollbars are added, to observe hidden parts of the canvas previously outside the canvas.
When s = turtle.Screen(), s.screensize(...) can be used as below.
The code line below, s.screensize(canvwidth=1200, canvheight=800, bg="yellow"), creates scrollbars and extends the canvas which is drawn in yellow around the background gif.
import turtle

s = turtle.Screen()
s.bgpic("docs/turtle/images/mario.gif")
s.title("Turtle Screen")
s.setup(width=800, height=600, startx=40, starty=20)

# turtle drawing
t = turtle.Turtle()
t.shapesize(10, 10, 12)
t.color("blue")
t.pensize(10)
t.penup(); t.setpos(-400, -250); t.pendown()
t.fd(800)

s.screensize(canvwidth=1200, canvheight=800, bg="yellow")

# same turtle - new drawing
t.color("red")
t.pensize(10)
t.penup(); t.setpos(-400, -285); t.pendown()
t.fd(800)

turtle.done()

Tasks

  1. Replace the screensize line above with s.setup(width=1200, height=800, startx=0, starty=0). What happens instead?

Replace the screensize line above with s.setup(width=1200, height=800, startx=0, starty=0). What happens instead?

No scroll bars are required as the screen window resizes and repositions to the topleft of the screen.

3.5. Animation control

See: https://docs.python.org/3/library/turtle.html#animation-control
Turn turtle animation on/off and set the delay for update drawings.
turtle.tracer(n=None, delay=None)
n - nonnegative integer; higher is faster; 0 to turn off tracing; default None
delay - nonnegative integer; default None
If n is given, only each n-th regular screen update is really performed. When called without arguments, returns the currently stored value of n. Second argument sets delay value (see delay()).
When s = turtle.Screen(), s.tracer(0, 0) can be used as below.
Set the delay for update drawings.
turtle.delay(delay=None)
Set or return the drawing delay in milliseconds. This is approximately the time interval between two consecutive canvas updates.
delay - positive integer; default None
When s = turtle.Screen(), s.delay(1000) can be used as below.
Update the screen. Use when tracing has been set to 0 to turn it off.
turtle.update()
Perform a TurtleScreen update. To be used when tracer is turned off.
When s = turtle.Screen(), s.update() can be used as below.
The code below turns off turtle animation and produces the image rapidly.
Try changing the tracer to s.tracer(1, 100) to compare.
import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("square")
s.setup(width=800, height=600, startx=0, starty=0)
s.tracer(0, 0)

t = turtle.Turtle()
t.speed(0)


def square(t, l=50, x=0, y=0):
    for _ in range(4):
        t.fd(l)
        t.rt(90)


for i in range(32):
    square(t, l=100)
    t.rt(6)

s.update()
s.exitonclick()

Tasks

  1. Add 2 lines of code to display the drawing without animation.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("square")
s.setup(width=800, height=600, startx=0, starty=0)

t = turtle.Turtle()
t.pencolor("blue")
t.speed(0)

def square(t, side, x=0, y=0):
    for _ in range(4):
        t.fd(side)
        t.rt(90)

for i in range(60):
    square(t, side=200)
    t.rt(6)

s.exitonclick()

Add 2 lines of code to display the drawing without animation.

import turtle

s = turtle.Screen()
s.bgcolor("white")
s.title("square")
s.setup(width=800, height=600, startx=0, starty=0)
s.tracer(0, 0)

t = turtle.Turtle()
t.pencolor("blue")
t.speed(0)


def square(t, side, x=0, y=0):
    for _ in range(4):
        t.fd(side)
        t.rt(90)


for i in range(60):
    square(t, side=200)
    t.rt(6)

s.update()
s.exitonclick()

3.6. Using screen events

Several other screen events are available.
listen()
onkey(); onkeyrelease()
onkeypress()
onclick(); onscreenclick()
ontimer()
See: https://docs.python.org/3/library/turtle.html#using-screen-events