Graphics API for Students of Python: GASP¶

Introduction¶

This sheet describes briefly all the graphics things (i.e., drawing pictures) you can easily do with the gasp module for Python. (You can actually do lots of other complicated graphics things with Python, but they’re, errrm, complicated. We’ve made a bunch of useful things easy using the gasp module, and these are what this sheet describes.)

There’s an introduction to graphics in Sheet 3 (Pretty Pictures), so this sheet is more a reference than an introduction. Some of it is very terse; ask a teacher if it doesn’t make any sense. (If you are a teacher or you are studying this on your own and it still doesn’t make any sense, feel free to send an email to jeff.elkner@gmail.com .)

Coordinates¶

(0, 0) is at the bottom left of the window, with y increasing as you go upwards and x increasing as you go rightwards. The window is 640 pixels by 480, by default. (You can make it a different size if you want to.) Coordinates are given in units of one pixel.

All functions that take coordinates take them as a tuple (x, y).

Circle((300, 200), 10)     # :) This is good
Circle(300, 200, 10)       # :( This is bad

Colors¶

To access the color module GASP has to offer. Call color.* where * is the color you wish to call. For example: color.BLACK This is the color black. You can also access colors as a string using the color.from_str(string) method.

Note: color names must be in ALL CAPS.

Check out the gasp color reference chart to see all of the available color options, or call color.available() to see the list of available colors. At their core, colors in GASP are HEX strings that specify which colors to draw on screen.

The Essentials¶

from gasp import *

begin_graphics()

...                         # all of your code

end_graphics()

These are the essentials. from gasp import * imports the gasp module, begin_graphics() starts the graphics window, and end_graphics() quits the graphics window and ends the program. It’s dead simple, but also dead necessary.

Graphics Functions¶

begin_graphics()¶

begin_graphics(width=800, height=600, background=color.YELLOW, title="My Game")

This creates a graphics window with the dimensions 800x600, a title of My Game , and a background color of yellow. With no arguments you get a white 640x480 graphics window titled Gasp .

width: The width of the window in pixels.
height: The windows height in pixels.
background: It is the background of the graphics window. It can either be a color or an image
title: A string that will be the title of the window.

end_graphics()¶

end_graphics()

Ends a graphics window.

clear_screen()¶

clear_screen()

Clears everything off of the graphics window. It looks like a new graphics window as if you just called begin_graphics().

remove_from_screen()¶

remove_from_screen(obj)

removes those objects from the screen

obj: A screen object of a list of screen_objects you would like to remove from the screen

Screen Objects¶

The objects that you will be displayed in your graphics window. You can manipulate these objects using the screen object methods

Plot¶

Plot(pos, color=color.BLACK, size=1)

It puts a dot on the screen.

pos: The coordinate on the screen that you wish to plot.
color: The color you wish the dot to be.
size: An integer that determines the size the of the dot

Line¶

Line(start, end, color=color.BLACK)

Creates a line on the screen.

start: The starting coordinate of the line.
end: The coordinate at which the line will end.
color: The color of the line
thickness: The thickness in pixels of your line.

Box¶

Box(corner, width, height, filled=False, color=color.BLACK, thickness=1)

This creates a Box on the screen

corner: A coordinate where the lower left corner of your box will be.
width: The width in pixels of the box.
height: The height of the box in pixels.
filled: A boolean value that determines if your box will be filled
color: The color of your box.
thickness: The thickness in pixels of your box’s lines.

Polygon¶

Polygon(points, filled=False, color=color.BLACK, thickness=1)

Creates a polygon on the screen

points: A list of coordinates that is each point on the polygon. The must be more than two items in the list
filled: A boolean value. If it is False the polygon will not be filled. Else, the polygon will not be filled
color: The color of the polygon’s lines
thickness: An integer that determines the thickness of the lines.

Circle¶

Circle(center, radius, filled=False, color=color.BLACK, thickness=1)

Draws a circle, its center is a set of coordinates, and the radius is in pixels. It defaults to not being filled and the color black.

center: The circle’s center coordinate.
width: An integer that is the radius of the circle
filled: A boolean value that determines if your circle will be filled
color: The color of your circle.
thickness: The thickness in pixels of the circles lines.

Arc¶

Arc(center, radius, start_angle, end_angle, filled=False, color=color.BLACK, thickness=1)

Creates an arc on the screen.

center: A coordinate that is the center of the arc.
radius: An integer that is the distance between the center and the outer edge of the arc.
start_angle: The start angle in degrees of the arc
end_angle: The end angle in degrees of your arc
filled: A boolean value that if True it fills the arc
color: The color the arc
thickness: The thickness in pixels of the arc

Oval¶

Oval(center, width, height, filled=False, color=color.BLACK, thickness=1)

Puts an oval on the screen wherever you want.

center: The center coordinate of the Oval
width: The width in pixels of the oval
height: The height of the oval in pixels
filled: A boolean value determining if the oval will be filled or not.
color: The oval’s color
thickness: The thickness of the ovals lines

Screen Object Methods¶

The methods that manipulates screen objects

move_to()¶

move_to(obj, pos)

Move a screen object to a pos

obj: A screen object you wish to move.
pos: The coordinate on the screen that the object will move to

move_by()¶

move_by(obj, dx, dy)

Move a screen object relative to it’s position

obj: The screen object you wish to move
dx: How much the object will move in the ‘x’ direction. Positive or negative.
dy: How much the object will move in the ‘y’ direction. A pixel value.

rotate_to()¶

rotate_to(obj, angle)

Rotate an object to an angle

obj: The screen object that will be rotated
angle: The angle in degrees that the object will be rotated to

rotate_by()¶

rotate_by(obj, angle)

Rotate an object a certain degree.

obj: The screen object you wish to rotate
angle: The degree that the object will be rotate. Can be positive or negative.

Text¶

Text()¶

Text(text, pos, color=color.BLACK, size=12)

Puts text on the screen

text: A string of the text that will be displayed
pos: The center coordinate of the text
color: The color of the text
size: The font size

Keyboard¶

keys_pressed()¶

keys_pressed()

returns a list of all of the keys pressed at that moment.

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