Detailed documentation for Half-Life physics
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_templates
images
static
.gitignore
Makefile
README.md
algorithms.rst
automation.rst
basicphy.rst
casestudies.rst
conf.py
damage.rst
deploy
duckjump.rst
entity.rst
explosions.rst
funcs.rst
game.rst
glossary.rst
gravitymotion.rst
index.rst
ladder.rst
monsters.rst
movement.rst
player.rst
practical.rst
snippets.rst
strafing.rst
surfing.rst
triggers.rst
weapons.rst

README.md

Half-Life Physics Documentation

Build Status

This repo contains the source files for the Half-Life physics documentation hosted at

Building

Install Sphinx, then run

make html

The generated files will be in _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.

Quality in research is paramount.

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
Reproducing HL21's gonarch Very high
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