OpenGL programming in Python: pyglpainter

This was a recent hobby programming project of mine for use in a CNC application, using Python and OpenGL. The source code is available at https://github.com/michaelfranzl/pyglpainter .Simple OpenGL output using pyglpainter library

This Python module provides the class PainterWidget, extending PyQt5’s QGLWidget class with boilerplate code neccessary for applications which want to build a classical orthagnoal 3D world in which the user can interactively navigate with the mouse via the classical (and expected) Pan-Zoom-Rotate paradigm implemented via a virtual trackball (using quaternions for rotations).

This class is especially useful for technical visualizations in 3D space. It provides a simple Python API to draw raw OpenGL primitives (LINES, LINE_STRIP, TRIANGLES, etc.) as well as a number of useful composite primitives rendered by this class itself ( Grid, Star, CoordSystem, Text, etc., see files in classes/items). As a bonus, all objects/items can either be drawn as real 3D world entities which optionally support “billboard” mode (fully camera-aligned or arbitrary- axis aligned), or as a 2D overlay.

It uses the “modern”, shader-based, OpenGL API rather than the deprecated “fixed pipeline” and was developed for Python version 3 and Qt version 5.

Model, View and Projection matrices are calculated on the CPU, and then utilized in the GPU.

Qt has been chosen not only because it provides the GL environment but also vector, matrix and quaternion math. A port of this Python code into native Qt C++ is therefore trivial.

Look at example.py, part of this project, to see how this class can be used. If you need more functionality, consider subclassing.

Most of the time, calls to item_create() are enough to build a 3D world with interesting objects in it (the name for these objects here is “items”). Items can be rendered with different shaders.

This project was originally created for a CNC application, but then extracted from this application and made multi-purpose. The author believes it contains the simplest and shortest code to quickly utilize the basic and raw powers of OpenGL. To keep code simple and short, the project was optimized for technical, line- and triangle based primitives, not the realism that game engines strive for. The simple shaders included in this project will draw aliased lines and the output therefore will look more like computer graphics of the 80’s. But “modern” OpenGL offloads many things into shaders anyway.

This class can either be used for teaching purposes, experimentation, or as a visualization backend for production-class applications.

Mouse Navigation

Left Button drag left/right/up/down: Rotate camera left/right/up/down

Middle Button drag left/right/up/down: Move camera left/right/up/down

Wheel rotate up/down: Move camera ahead/back

Right Button drag up/down: Move camera ahead/back (same as wheel)

The FOV (Field of View) is held constant. “Zooming” is rather moving the camera forward alongs its look axis, which is more natural than changing the FOV of the camera. Even cameras in movies and TV series nowadays very, very rarely zoom.