Half-Life Physics Reference

This repo contains the source files for the Half-Life physics documentation hosted at https://www.jwchong.com/hl/.

Building

Install python. Then first create a python venv folder:

$ python -m venv venv

Activate the venv:

$ . ./venv/bin/activate

Then install the packages:

$ pip install -r requirements.txt

Install the node packages needed for the MathJax rendering script:

$ yarn install

To build the HTML files, run

$ python build.py build

How to contribute

You are encouraged to help out this documentation by researching and writing. You will be credited. This project will be kept online for as long as I'm alive. You can begin by checking out the list of topics below and research the ones you find interesting, or simply look at the empty sections of the documentation and contribute to research and writing for it.

Difficulty	Meaning
Low	Requires a few hours worth of effort to gain a thorough understanding
Medium	Requires a few days worth of focused effort to gain a thorough understanding
High	Requires a few days to a few weeks worth of focused effort, while possessing prerequisite knowledge and skills, to gain a reasonable level of understanding
Very high	Requires a few weeks to a few months worth of focused effort, while possessing deep prerequisite knowledge and skills, to gain a reasonable level of understanding
Extremely high	Requires months or years of focused effort, while possessing expert-level understanding of relevant Half-Life physics and very well trained on specific mathematical skills, to make meaningful contributions

Engine internals

Engine internals are generally tedious to research on due to the unavailability of source code.

Topic	Issues	Difficulty
Loading, saving, level change		High
Save warping		Medium
BSP collision structure in memory		High
Tracing		High
Frame walkthrough		High
0ms frames		Medium
Network messages and DELTA		Medium
Demos		Medium

Movement physics

Naturally, movement physics are some of the most maths-heavy parts of Half-Life physics, and thus some of these topics may be very difficult and require a high level of skill and knowledge.

Topic	Issues	Difficulty
Surfing		Extremely high
Ducktapping on stairs		High
Entity movements		Medium
Base velocity		Medium
Optimal ladder side exit		High
Optimal tight strafing		Very high
Optimal vent movement with bunnyhop cap		High
Optimal damage boost timing		High
Computing optimal route		Extremely high
Constrained vectorial compensation		High
Implementation of autoactions		High
Characterising human strafing		Very high

Weapons

Some of these topics may require some mathematics, and others may require an understanding of engine internals.

Topic	Issues	Difficulty
Optimal snark climbing		Very high
Hornet manipulation and penetration		Medium
Crowbar		Low
Exact selfgauss conditions		High
Exact nuking conditions		High
Tripmines		Low
Rockets		Medium
Mid-air projectile collisions		Very high

Entities

Understanding entities may require venturing into the engine, which again, may be tedious.

Topic	Issues	Difficulty
func_wall vs worldspawn		Medium
trigger_once and trigger_multiple		Medium
trigger_push		Medium
How moving platforms carry entities		Medium
func_rotating (and friends) crushing mechanism		Medium
Multimanager and scripting		Medium

Monsters

A monster refers to an entity that has an AI, both friendly and unfriendly. Researching on AI can be very tedious due to the complex interactions between different parts of the code.

Topic	Issues	Difficulty
Node graphs and monster movements		High
Enemy behaviour		High
Talkmonster behaviour		High
Why models affects behaviour		High
Ammo duplication with save loading, and reportedly without		High

TAS

TAS topics are generally long term.

Topic	Issues	Difficulty
Better TAS process and tools		Very high
Application of ML		Extremely high

Licence

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.