Graphix Module - Collision Detection Extension

A collision detection extension for the University of Portsmouth's graphix module, adding axis-aligned bounding box (AABB) collision detection with normal vector calculations.

Overview

This contribution integrates collision detection directly into the move() method of graphical objects, enabling real-time collision detection and physics-based responses for games and simulations.

Features

• AABB Collision Detection: Efficient axis-aligned bounding box collision detection for rectangles, ovals, and circles
• Normal Vector Calculation: Returns collision normal vectors for physics-based responses (bouncing, sliding, etc.)
• Integrated Move Method: Collision detection happens automatically during movement
• Simple API: Enable collision detection with a single property

Installation

1. Replace your existing graphix.py with the modified version
2. No additional dependencies required - works with standard Python and Tkinter

Usage

Basic Collision Detection

from graphix import Window, Rectangle, Point

win = Window("Collision Demo", 400, 400)
a = Rectangle(Point(50, 50), Point(150, 150))
b = Rectangle(Point(200, 200), Point(300, 300))

a.collision = True
b.collision = True

a.draw(win)
b.draw(win)

collision, normal = a.move(10, 10)
if collision:
    print(f"Collision detected! Normal vector: {normal}")

Methods

move(dx: int, dy: int) -> tuple[bool, tuple[int, int]]

Moves the object and checks for collisions.

Parameters:

• dx: Units to move in x direction
• dy: Units to move in y direction

Returns:

• tuple[bool, tuple[int, int]]: (collision, normal_vector)
  • collision: False if no collision occurred, True if collision detected
  • normal_vector: (nx, ny) - Normal vector at collision point (for physics calculations)

Examples

See sample/ball.py for a complete bouncing ball simulation demonstrating collision detection with normal vectors.

Understanding Normal Vectors

Normal vectors indicate the direction perpendicular to the collision surface. They are essential for:

• Bouncing: Reflect velocity using the normal vector
• Sliding: Project movement along surfaces
• Physics simulations: Calculate collision responses

Recommended Reading

• Vector Mathematics for Game Developers
• 2D Collision Response
• AABB Collision Detection Explained

Limitations

Not Supported

• Rotated objects: Collision detection only works for axis-aligned shapes (no rotation)
• Concave polygons: Requires convex collision detection (not yet implemented)
• Collision groups: Not yet implemented (planned for future release)

Supported Objects

• Rectangle
• Oval
• Circle

Roadmap

• Collision groups (objects only collide with specific groups)
• Polygon collision support
• Rotated object support (OBB - Oriented Bounding Boxes)

Contributing

This is an open-source contribution! Feel free to:

• Fork and extend functionality
• Add new collision mechanics
• Improve performance
• Fix bugs
• Add tests

Credits

Please maintain attribution to original contributors when forking or extending this work.

License

This extension follows the same license as the original graphix module (GPL).

Acknowledgments

• Original graphix module by John Zelle
• Modified for University of Portsmouth M30299 Programming module
• Collision detection extension contributed to the community

Support

For issues, questions, or suggestions:

• Open an issue on the repository
• Contact me on the University Discord

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