PIDDLE

Plug-In Drawing, Does Little Else

Abstract

PIDDLE is a Python module for creating two-dimensional graphics in a manner that is both cross-platform and cross-media; that is, it can support screen graphics (e.g. QuickDraw, Windows, Tk) as well as file output (PostScript, PDF, GIF, etc.). It makes use of the native 2D drawing calls of each backend, for maximum efficiency and quality. It works by defining a base class (piddle.Canvas) with methods for all supported drawing primitives. A particular drawing context is provided in the form of a derived class. PIDDLE applications will be able to automatically select an appropriate backend for the user's environment.

[The most up-to-date version of this document can be found via the Piddle home page at http://piddle.sourceforge.net]

Status

PIDDLE is beginning beta testing. It should be stable now, though there may be a few bugs still lurking here or there -- if you find any, please send email to the PIDDLE mailing list at pythonpiddle@egroups.com .

The latest stable PIDDLE distribution is available from our Source Forge download page here. You may also want to look at CVS access and other information for developers if you want the latest experimental version.

As of 10 February 2000, the current release is 1.0.b1 -- see the version history to see what's new.

Please note that PIDDLE requires Python 1.5.2, because it uses the "extend" list method, which is not available in older versions of Python.

The standard distribution includes the following back-end renderers:

Backend	Requires	Contact	Interactive?	Notes
PDF		Andy Robinson	No
PIL	PIL	Joe Strout	No
QuickDraw	MacPython	Joe Strout	Yes
PostScript		Chris Lee	No
Illustrator		Bill Bedford	No
piddleVCR		Joe Strout	No
OpenGL	PyOpenGL	David Ascher	Yes
Tk	Tkinter	Perry Stoll	No	[1]
wxWindows	wxPython	Kevin Jacobs	Yes

Notes:

[1]

The following backends are in various stages of development, and not yet part of the standard distribution.

name	author	strings	images	interactive
GTK+	Fred L. Drake, Jr.	Y/N [6]	N	Y
Pythonwin	Andy Robinson	Y [5]	N	N

Notes:

[5]

[6] piddleGTK doesn't yet draw rotated strings, but it is planned.

Usage Overview

PIDDLE is designed for vector graphics -- i.e., drawing of primitives such as lines and ellipses, rather than manipulation of individual pixels. Generally, one creates a PIDDLE drawing in three steps:

instantiate a class derived from piddle.Canvas
call drawing methods on that object, such as drawLine or drawString
flush the canvas's buffer (i.e., update the file, screen, or whatever)

Note that while PIDDLE is easiest to use in a noninteractive mode -- i.e., simply generating charts, pictures, or other static displays -- some backends support callback methods invoked when the mouse moves over or clicks on the drawing. This allows for some graphical interaction with the user.

Developer's Overview

Creating a new PIDDLE backend is relatively easy. You must create a class derived from piddle.Canvas, and instantiate at least the following methods:

drawLine
drawPolygon
drawImage
drawString

All other drawing methods will have default implementations in terms of the functions above. However, you may wish to also override other drawing methods for the sake of efficiency or quality.

Documentation

PIDDLE White Paper

PIDDLE Reference Manual

In addition, information specific to individual backends are placed in the docs/notes* directories

Examples

This example illustrates a hodgepodge of PIDDLE drawing commands, including lines, curves, polygons, arcs, roundrects, and rotated text. The graphic shown here was rendered with the QuickDraw backend; other backends may vary, especially in the appearance of the text.
This spectrum chart is actually a useful program; I needed to generate a spectrum for a scientific application, and this is the PIDDLE program I used to do it. In this program, I defined a factory function 'makeCanvas' at the top of the program to create the canvas. To use a backend other than QuickDraw, you'll only need to modify this function.
A string test module puts PIDDLE's font and string handling through the paces. It illustrates the standard fonts which every backend should be able to understand (and hopefully display).
A string rotation test module exercises the drawing of rotated strings at a variety of angles (in rainbow colors, no less). Example output is shown for both QuickDraw and PIL. Note that the two have somewhat different ideas about how big a 12-point (default) font should be; this sort of discrepancy is inevitable, at least for now.

More examples are included with the distribution in the examples directory and in piddletest.py, a file which allows you to select any test, and pair it with any standard backend renderer.

Credits & Feedback

PIDDLE was initially designed and implemented by a small international team of Python coders. There is a mailing list for discussion of PIDDLE at http://www.egroups.com/list/pythonpiddle/. To get your feedback to the list send email to pythonpiddle@egroups.com .