OmniCanvas is a Python canvas which supports basic two-dimensional graphics, and outputs to various graphics formats - currently just SVG.
>>> import omnicanvas >>> canvas = omnicanvas.Canvas(700, 400) >>> canvas.add_rectangle(10, 20, 300, 200, fill_color="#CC0000") >>> canvas.graphics()[0] <Rectangle 300×200 at (10,20)> >>> canvas.save("example.svg")
See the the examples for more examples, or the full API for a full listing of features.
OmniCanvas can be installed using pip:
$ pip3 install omnicanvas
OmniCanvas is written for Python 3, and does not support Python 2.
If you get permission errors, try using sudo:
$ sudo pip3 install omnicanvas
The repository for OmniCanvas, containing the most recent iteration, can be found here. To clone the OmniCanvas repository directly from there, use:
git clone git://github.com/samirelanduk/omnicanvas.git
OmniCanvas currently has no external dependencies, and is pure Python.
The Canvas class is the first thing you will need to create - it is the base upon which everything else is created. If you've ever used HTML or GUI canvases, they work in much the same way.
>>> import omnicanvas >>> canvas = omnicanvas.Canvas(600, 400) >>> canvas.width() 600 >>> canvas.height() 400
Canvases need width and height information, in pixels. You can also specify the background color:
>>> canvas = omnicanvas.Canvas(600, 400, background_color="#0000DD") >>> canvas.background_color() '#0000DD'
Canvases contain a list of graphics (which all inherit from class Graphic), and it is these objects which make up the image.
Currently, there are the following types.
Rectangle objects are... rectangles. Boxes, defined with the coordinates of their top-left corner, and width and height:
>>> canvas.add_rectangle(10, 10, 300, 200) >>> canvas.graphics()[0] <Rectangle 300×200 at (10,10)> >>> canvas.graphics()[0].width() 300
Rectangles inherit from ShapeGraphic which means they have a fill color and opacity:
>>> canvas.add_rectangle(10, 10, 300, 200, fill_color="#3344EE", opacity=0.5) >>> canvas.graphics()[-1].fill_color() '#3344EE' >>> canvas.graphics()[-1].opacity() 0.5
They also, like all classes which inherit from class Graphic, have properties relating to their lines:
>>> canvas.add_rectangle(10, 10, 300, 200, line_width=2, line_style="--") >>> canvas.graphics()[-1].line_width() 2 >>> canvas.graphics()[-1].line_style() '--' >>> canvas.graphics()[-1].line_color("#FFFF00") >>> canvas.graphics()[-1].line_color() '#FFFF00'
Oval objects represent circles and ovals generally. They are defined by the bounding rectangle around them.
>>> canvas.add_oval(10, 10, 300, 200) >>> canvas.graphics()[0] <Oval 300×200 at (10,10)> >>> canvas.graphics()[0].width() 300
Like Rectangles they also have properties relating to their interior space and their edges.
Line objects are even more straightforward. They are lines defined by a start coordinate and an end coordinate:
>>> canvas.add_line(10, 10, 90, 90) >>> canvas.x1() 10 >>> canvas.y1() 10 >>> canvas.x2() 90 >>> canvas.y2() 90
Lines inherit directly from Graphic and have the same properties relating to line width etc. as above.
Polygon objects are two-dimensional shapes with an arbitrary number of points. These are given as a sequence of coordinates:
>>> canvas.add_polygon(60, 60, 90, 120, 30, 120) # Creates a triangle >>> canvas.graphics()[-1].coordinates() (60, 60, 90, 120, 30, 120) >>> canvas.graphics()[-1].coordinates(xy_pairs=True) ((60, 60), (90, 120), (30, 120))
You must supply an even number of points, and there must be at least three vertices.
Otherwise they behave much like Rectangles - they inherit from Graphic and so have the above properties relating to fill and border.
Text objects are used to hold text. Unlike other Graphics, their default fill_color is black, not white, and their default line_width is 0, not 1.
>>> canvas.add_text(50, 50, "OmniCanvas is sexy", font_size=32) >>> canvas.graphics()[-1].text() 'OmniCanvas is sexy' >>> canvas.graphics()[-1].font_size() 32 >>> canvas.graphics()[-1].fill_color() '#000000' >>> canvas.graphics()[-1].line_width() 0
The coordinate given by default will be the centre of the text. This can be changed by specifying the desired horizontal and vertical alignment:
>>> canvas.add_text(50, 50, "X", vertical_align="top", horizontal_align="left")
These are very similar to Polygon, except the last vertex is not joined to the first one, and so they have no interior space. They are just lines with an arbitrary number of vertices.
They behave very similarly to Polygons:
>>> canvas.add_polyline(60, 60, 90, 120, 30, 120) >>> canvas.graphics()[-1].coordinates() (60, 60, 90, 120, 30, 120) >>> canvas.graphics()[-1].coordinates(xy_pairs=True) ((60, 60), (90, 120), (30, 120))
All of the above graphic adding methods will return the graphic they have just added, if you need a reference to it later.
>>> rectangle = canvas.add_rectangle(10, 10, 300, 200) >>> rectangle <Rectangle 300×200 at (10,10)>
Additionally, all graphics can be given names, which can then be used to retrieve them from the Canvas using two methods -~.canvas.Canvas.get_graphic_by_name and ~.canvas.Canvas.get_graphics_by_name:
>>> canvas.add_line(10, 10, 90, 90, name="Line 1") >>> canvas.add_line(20, 10, 90, 90, name="Line 2") >>> canvas.add_line(10, 20, 90, 90, name="A Line") >>> canvas.add_line(20, 20, 90, 90, name="A Line") >>> canvas.get_graphic_by_name("Line 1") <Line (10,10) to (90,70)> >>> canvas.get_graphic_by_name("Line 2") <Line (20,10) to (90,70)> >>> canvas.get_graphic_by_name("A Line") <Line (10,20) to (90,70)> >>> canvas.get_graphics_by_name("A Line") [<Line (10,20) to (90,70)>, <Line (20,20) to (90,70)>]
Once the canvas has been decorated with whatever Graphics you see fit, it can be saved to file:
>>> canvas.save("example.svg")
Most browsers will have no trouble displaying SVG files once created.
If you want to get the text of the SVG directly, you can use the to_svg() method of canvases, which will return this raw text.
22 January 2017
- Added Oval Graphic.
- Graphic objects can now be reordered by the Canvas.
- There are now pleasant colour constants.
15 December 2016
- Fixed inconsistency in whether the central vertical alignment is 'middle' or 'center'
14 December 2016
- Graphics adding methods now return a reference to the graphic just added.
- Added names to graphics, and methods for retrieving them from the canvas by name.
12 December 2016
- All attributes are now method properties.
- Added function for converting HSL colours to RGB strings.
- Added Polyline Graphic.
6 June 2016
- Canvas with four graphic types:
- Rectangles
- Lines
- Polygons
- Text
- SVG output