Collision Detection in Game Design

Teaching material for C++4 in Game Design, covering discrete and continuous 2D collision detection through interactive Raylib visualizers and two practical workshops.

• Author: Eliel Camargo-Molina
• Course: C++4 in Game Design
• Original course edition: September–October 2025
• Repository edition: 1.0.0

What is included

Order	Module	Main ideas	Student activity
1	Discrete collision lecture	MTVs, circles, AABBs, OBBs, convexity, SAT	Explore five interactive visualizations
2	Breakout SAT workshop	Circle–convex SAT and collision response	Implement one SAT narrow-phase function
3	Continuous collision lecture	TOI, slabs, quadratics, relative motion, Minkowski sums, swept AABBs	Explore six CCD visualizations
4	Plinko CCD workshop	Broad phase, narrow phase, earliest collision	Assemble a CCD collision pipeline

The repository includes both starter and solution executables for each workshop. See TEACHING_GUIDE.md for suggested delivery.

Prerequisites

• A C++17 compiler
• CMake 3.20 or newer
• Git and an internet connection during the first configuration

Raylib 5.5 is downloaded automatically by CMake. No global Raylib installation is required.

Build everything

cmake -S . -B build
cmake --build build --parallel

Executables are placed in build/bin (build/bin/Debug with some multi-configuration generators):

• lecture1_visualizer
• breakout_starter
• breakout_solution
• lecture2_visualizer
• plinko_starter
• plinko_solution

To build only one target:

cmake --build build --target breakout_starter

Workshop workflow

The starter targets deliberately compile with incomplete student functions:

• Breakout: implement CirclePoly_SAT_MTV in workshops/01-breakout-sat/collision_engine.cpp.
• Plinko: implement FindEarliestCollision in workshops/02-plinko-ccd/workshop.cpp.

Completed versions are kept in separate *_solution.cpp files. They are not needed by the starter targets.

Shared conventions

• Touching counts as a collision.
• Collision normals point from the first object (A) toward the second (B).
• To move A out of B, use -normal * depth.
• CCD times are normalized to the current frame: t is in [0, 1].
• All polygon SAT examples assume convex polygons.

Scope and limitations

These are teaching examples, not a production physics engine:

• Breakout uses discrete collision detection and can tunnel at extreme speeds.
• The examples resolve one selected contact at a time rather than constructing a full contact manifold.
• Plinko stops at the first impact in a frame and does not consume the remaining frame time after the bounce.
• The broad phase in Plinko scans all pegs; the swept bounds reduce expensive narrow-phase tests but are not a spatial acceleration structure.

Attribution, citation, and licenses

The teaching material was created by Eliel Camargo-Molina for C++4 in Game Design. See ATTRIBUTION.md for third-party notices and CITATION.cff for citation metadata.

• C++ source and build files: MIT License
• Notes and teaching documentation: CC BY 4.0

See LICENSE.md for the file-by-file license mapping.