Sonic Physics Guide

Introduction

Welcome to the Sonic Physics Guide, a comprehensive resource dedicated to describing the inner workings of the classic Genesis & Sega CD Sonic games, along with Sonic Mania. Here, the intricate details of how the game's physics function are thoroughly explored, providing in-depth explanations about the exact values and rules and precise speed values governing Sonic's movements, 360 slope physics, Badnik & object behaviour, all the way to the construction of the sloped terrain. The guide will shed light on exactly how every aspect, from navigating slopes and loops to interacting with Springs, contributes to the gameplay.

Whether you're a curious newcomer, an experienced fan game developer, or a seasoned Sonic fan seeking a deeper understanding of the games, this guide aims to present the information in an accessible manner, providing clear and concise breakdowns of the underlying concepts.

This guide will present these physics rules in an engine-agnostic manner, focusing on the tangible results of the game logic instead of delving into the minutiae of how the original 68k assembly code operated. As a result, these rules can be applied to modern programming languages such as Java, C, C++, Python, or a Lisp dialect when implementing the physics described in this guide. Moreover, individuals using this guide will be able to easily utilise specialised engines/IDEs such as GameMaker, Unity, Godot, Clickteam Fusion, or Love2D to implement the described game rules. Nevertheless, it is important to note that this guide will still acknowledge the quirks, limitations, and workarounds that were necessary for the original game due to its utilisation of a low-level programming language.

Physics Guides

General

Basics
A prerequisite for much of the info on this guide, including common object variables, how angles work, how object sizes are displayed, and more.

• Positions And Speeds
• Angles
• Variables

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 things for an extremely close recreation, they are necessary for absolute accuracy

• Pixel and Subpixel
• Hex Angles

Characters
Information about specific characters and their constants, variables, sizes, and jump height.

• Sonic
• Tails
• Knuckles

Gameplay

These guides will explain what happens during gameplay scenarios, such as slope collision, player movement, and object interactions.

Collision

Solid Tiles
Terrain Part 1: A detailed description of the individual building blocks of terrain, and how they are processed and detected.

• Sensors

Solid Terrain

Terrain Part 2: How Solid Tiles and collison layers are used to construct slopes, loops, and other structures.

• Layers
• Loops

Slope Collision
Slopes Part 1: How the Player object uses their sensor arrangement to detect and react to terrain, including 360° slopes such as walls and ceilings, and collision while airborne.

• The Player's Sensors
• While Grounded
  • 360 Degree Collision
• While Airborne

Hitboxes
Object hitboxes, the Player's hitbox, and other ways objects directly interact with the player other than solidity.

• The Player's Hitbox
• Trigger Areas

Solid Objects
Object solidity, jump through platforms, and sloped variants of each.

• Solid Objects
• Sloped Objects
• Jump Through Platforms
• Pushable Blocks
• Item Monitor

Physics

Slope Physics
Slopes Part 2: How the Player moves with momentum over angled surfaces.

• Moving Along Slopes
• 360 Degree Movement
• Falling and Slipping Down Slopes
• Landing On The Ground

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.

• Air
• Physics

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.

• Badniks
• Bosses

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.

• Spindash
• Super Peel Out
• Drop Dash
• Insta-Shield
• Flying
• Gliding
• Climbing

Elemental Shields
Elemental Shield abilities, powers, and moves.

• Flame Shield
• Bubble Shield
• Lightning Shield

Player 2
How the second Player will follow you throughout stages, and how they respawn when they fall offscreen.

• Player 2 CPU
• Respawning

Special Stages
Special stages including the rotating mazes from Sonic 1.

• Rotating Maze

Presentation

Camera
Camera mechanics when following the Player.

Animations
Animations system, and specific animation timings & rules.

• Animation System
• Variable Speed Animation Timings
• Normal Animation Timings
• Animation Rules

Special

Overlay Scripts
Lua scripts which overlay the game in an emulator for an interactive visual of collision.

• Sonic 1 Overlay
• Sonic 2 Overlay