Sonic Physics Guide
From Sonic Retro
ROM Hacks make the process of developing a functional Sonic game with unique art, enemies, and modifications much easier, since the game engine and basic mechanics are already functional. However, if the game requires a different game engine, modifying existing low-level assembly may be inappropriate, and some game designers might choose to program their own unique game engine. The physics of a game engine are rules that describe how to transform the Player's input (either in the form of buttons, keyboard, or even a mouse if the designer feels inclined) into appropriate changes in the position of the sprites in the game (such as the Sonic sprite, or alternatively, how enemy sprites will respond). These physics guides will hopefully make the process of simulating the rules used in Sonic games easier.
Since the rules themselves are independent of how they are implemented, many people choose programming languages such as Java, C, C++, Python, or a Lisp dialect to implement game physics. In addition, people can choose to use more specialized applications like Adobe Flash (Animate), GameMaker Studio 2, or a Clickteam program like Multimedia Fusion 2.
Hopefully, these guides will provide adequate information to facilitate implementation.
Contents
Physics Guides
General
Basics
A prerequisite for much of the info on this guide, including common variables, how angles work, how object sizes are displayed, and more.
Calculations (Technical)
A detailed explanation of how values like speeds, positions, and angles are stored and calculated in the original games. While it is not necessary to emulate these things to create an extremely accurate recreation, it can be useful to know for absolute pinpoint accuracy.
Characters
Information about specific characters and their constants, variables, sizes, and jump height.
Collision
Solid Tiles
Terrain Part 1: A detailed description of the individual building blocks of terrain and how they are processed detected.
- Terrain Part 2: How Solid Tiles and collison layers are used to construct slopes, loops, and other structures.
Slope Collision
Slopes Part 1: How the Player object uses its sensor arrangement to detect and react to sloped terrain.
Hitboxes
Object hitboxes, the Player's hitbox, and other ways objects directly interact with the player other than solidity.
Solid Objects
Object solidity, jump through platforms, and sloped variants of each.
Physics
Slope Physics
Slopes Part 2: How the Player moves with momentum over angled surfaces, and 360° movement along extreme slopes such as walls and ceilings.
Running
Physics & control of the Player while walking/running.
Rolling
Physics & control of the Player while rolling.
Air State
Physics & control of the Player while they are in the air.
Jumping
Physics & control while Jumping, how controllable jump height is achieved, and jumping at angles.
Getting Hit
What happens when the Player gets hit or dies.
Rebound
Physics when bouncing off enemies, bosses and other destroy-able items.
Underwater
Physics underwater, and how their remaining air is depleted.
Super Speeds
The Player's speeds and abilities when super.
Gameplay
Main Game Loop
The order that objects update each frame, and order of specific events like Player collision and movement.
Game Objects
Mechanics and sizes for things like rings, pushable blocks, buttons, and springs. How they are constructed, function, and interact with the Player.
Game Enemies
Badnik and bosses behaviour, collision, and specific interaction with the Player.
Ring Loss
Ring dispersal mechanics and physics when lost.
Special Abilities
General special abilities such as spindashing, and also detailing how character specific moves work.
Elemental Shields
Elemental Shield abilities, powers, and moves.
Special Stages
Special stages including the rotating mazes from Sonic 1.
Presentation
Camera
Camera mechanics when following the Player.
Animations
Animations system, and specific animation timings & rules.
Special
Overlay Scripts
Lua scripts which overlay the game in an emulator for an interactive visual of collision.