Defining costumes

A Sprite has Costumes and the Stage has Backdrops. Both Sprites and the Stage can have Sounds. The way that you define these in Pytch is quite flexible, but for most situations you will be able to use a very simple approach.

Suppose you have added an image called happy-kitten.jpg to your project, and you want to use this image as a costume for a sprite Kitten. You can do so like this:

import pytch

class Kitten(pytch.Sprite):
    Costumes = ["happy-kitten.jpg"]

This brings in your happy-kitten.jpg file as a costume for the Kitten Sprite. Pytch automatically switches to the first Costume when building and launching the project, showing it in the centre of the Stage.

Advanced Costume specifications

Sometimes you need more control over how Pytch uses your image as a costume. You can use the following variations independently for each costume of a sprite.

Specifying the origin of the costume

By default, Pytch chooses the centre of your image as the origin of your Sprite. When you say go_to_xy(100, 80), for example, it is the origin of the costume which ends up at the position (100, 80).

Sometimes you would like a different point in your image to be the origin. You can tell Pytch this by using a three-element tuple as a costume specification. For example,

import pytch

class Spaceship(pytch.Sprite):
    Costumes = [("rocket.png", 10, 20)]

will make the origin of the rocket costume be 10 pixels right and 20 pixels down from the top-left corner of the image. Notice that the ‘y’ coordinate goes down, rather than the usual ‘positive is up’ convention for the stage. This is to follow the usual convention for computer images, which uses (0, 0) as the top-left corner.

Specifying the label of the costume

In this example:

import pytch

class RacingCar(pytch.Sprite):
    Costumes = ["car.png", "crash.png"]

you will be able to say self.switch_costume("car") or self.switch_costume("crash") in a RacingCar method. Pytch uses the stem of the filename as the costume’s label. You might want to refer to these costumes by different labels instead. To do that, give a two-element tuple for a costume, like this:

import pytch

class RacingCar(pytch.Sprite):
    Costumes = [
        ("fast-car", "car.png"),
        ("crashed-car", "crash.png"),

With these specifications, you now say self.switch_costume("fast-car") or self.switch_costume("crashed-car") in your code.

Specifying the label and the origin of the costume

If you want to control both the label and the origin, give a four-element tuple, such as:

import pytch

class Hero(pytch.Sprite):
    Costumes = [("running", "running-person.jpg", 25, 30)]

This will give a costume based on the image running-person.jpg, which you will switch to with self.switch_costume("running"), and whose origin is the point 25 pixels from the left and 30 pixels from the top of the image.