Gizeh - Cairo for tourists

Gizeh is a Python library for vector graphics:

# Let's draw a red circle !
import gizeh
surface = gizeh.Surface(width=320, height=260) # in pixels
circle = gizeh.circle(r=30, xy= [40,40], fill=(1,0,0))
circle.draw(surface) # draw the circle on the surface
surface.write_to_png("circle.png") # export the surface as a PNG

You can see examples of Gizeh in action (combined with MoviePy to make animations) in this blog post.

Gizeh is written on top of the module cairocffi, which is a Python binding of the popular C library Cairo. Cairo is powerful, but difficult to learn and use. Gizeh implements a few classes on top of Cairo that make it more intuitive.

Gizeh should work on any platform and with python 2 and 3.

Installation

To use Gizeh you must first install Cairo on your computer (see their website).

Gizeh depends on the Python packages cairocffi and Numpy. They will both be automatically installed (if they aren't already) during the installation of Gizeh. If you have trouble with the installation, head to the last section of this README for troubleshooting. If it doesn't help, you can ask for help on Github.

Installation from the sources: Gizeh can be installed by unzipping the source code in some directory and using this command in the same directory:

(sudo) python setup.py install

Installation with pip: Alternatively, you can install Gizeh directly from the Python Package Index with this command:

(sudo) pip install gizeh

This method may fail if ez_setup is not installed on your computer. In this case install ez_setup first, with

(sudo) pip install ez_setup

Contribute !

Gizeh is an open-source software written by Zulko and released under the MIT licence. The project is hosted on Github. Everyone is welcome to contribute !

User Guide

This guide, along with the examples in the gizeh/examples folder, should give you everything you need to get started. To go further, read the function docstrings.

Surfaces

A Surface is a rectangle of fixed dimensions (in pixels), on which you will draw elements, and that you can save or export as an image:

import gizeh

# initialize surface
surface = gizeh.Surface(width=320, height=260) # in pixels

# Now make a shape and draw it on the surface
circle = gizeh.circle(r=30, xy= [40,40], fill=(1,1,1))
circle.draw(surface)

# Now export the surface
surface.get_npimage() # returns a (width x height x 3) numpy array
surface.write_to_png("circle.png")

Elements

Basic elements are circles, rectangles, lines, texts, etc., that you can draw on a surface using my_element.draw(surface). You can specify the properties and coordinates of these elements at creation time:

• xy : coordinates of the center of the object. At rendering time (in function surface.write_to_png) you can set the parameter y_origin to top (default) or bottom. If you leave it to top, (0,0) corresponds to the upper left corner of the final picture, and the bottom right corner has coordinates (width, height). If you choose y_origin=bottom, (0,0) will be at the bottom left of the picture (like in a standard plot) and (width, height) will be at the upper right corner.
• angle : angle (in radians) of the rotation of the element around its center xy.
• fill : what will fill the element (default is no fill). Can be a color (R,G,B), a color gradient, an image, etc. See section below.
• stroke : What will fill the element's contour. Same rules as for fill.
• stroke_width : the width (in pixels) of the element's contour. Default is 0 (no stroke).

Examples of elements:

Pi = 3.14
circ = gizeh.circle(r=30, xy=(50,50), fill=(1,1,1))
rect = gizeh.rectangle(lx=60.3, ly=45, xy=(60,70), fill=(0,1,0), angle=Pi/8)
sqr = gizeh.square(l=20, stroke=(1,1,1), stroke_width= 1.5)
arc = gizeh.arc(r=20, a1=Pi/4, a2=3*Pi/4, fill=(1,1,1))
text = gizeh.text("Hello world", fontfamily="Impact",  fontsize=40,
                  fill=(1,1,1), xy=(100,100), angle=Pi/12)
polygon = gizeh.polygon(r=40, n=5, angle=np.pi/4, xy=[40,50], fill=(1,0,1))
line = gizeh.polyline(points=[(0,0), (20,30), (40,40), (0,10)], stroke_width=3,
                     stroke=(1,0,0), fill=(0,1,0))

Fill and stroke

When you make a shape, the fill and stroke parameters can be one of the following:

• A RGB color of the form (r,g,b) where each element is comprised between 0 and 1 (1 is 100%).
• A RGBA color of the form (r,g,b,a), where a is comprised between 0 (totally transparent) and 1 (totally opaque).
• A gizeh.ColorGradient (see the docstring).
• A gizeh.ImagePattern, i.e. an image (see the docstring).
• A numpy array representing a RGB or RGBA image (not implemented yet).
• A PNG image file (not implemented yet).

Transformations

Any element can be transformed (translated, rotated or scaled). All transformations are outplace: they do not modify the original element, they create a modified version of it.

Examples:

square_1 = gizeh.square(l=20, xy = [30,35], fill=(1,0,0))
square_2 = square_1.rotate(Pi/8) # rotation around [0,0] by default
square_3 = square_2.rotate(Pi/4, center=[10,15]) # rotation around a center
square_4 = square_1.scale(2) # two times bigger
square_5 = square1.scale(sx=2, sy=3) # width times 2, height times 3
square_6 = square_1.scale(2, center=[30,30]) # zoom: scales around a center
square_7 = square_1.translate(xy=[5,15]) # translation

Groups

A Group is a collection of elements which will be transformed and drawn together. The elements can be a basic element (square, circle...) or even groups.

Examples:

square = gizeh.square(l=20, fill=(1,0,0), xy=(40,40))
circle = gizeh.circle(r=20, fill=(1,2,0), xy=(50,30))
group_1 = gizeh.Group([square, circle])
group_2 = group.translate(xy=[30,30]).rotate(Pi/4)
group_3 = gizeh.Group([circle, group_1])

surface = gizeh.Surface(width=300,height=200)
group.draw(surface)
group_1.draw(surface)
group_2.draw(surface)
group_3.draw(surface)
surface.write_to_png("my_masterwork.png")

That's all folks !

That's about all there is to know. To go further, see the examples in the examples folder or (wishful thinking) on the Web.

Installation support

Sometimes the installation through pip fails because

Some people have had problems to install cairocffi, Here is how they solved their problem:

On Debian/Ubuntu

sudo apt-get install python-dev python-pip ffmpeg libffi-dev
sudo pip install gizeh

On macOSX

pip install ez_setup


brew install pkg-config libffi
export PKG_CONFIG_PATH=/usr/local/Cellar/libffi/3.0.13/lib/pkgconfig/

# go to https://xquartz.macosforge.org and download and install XQuartz,
# which is needed for cairo, then...
brew install cairo

pip install gizeh