Sonic Physics Guide

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.

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.

• 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 these things to create an extremely accurate recreation, it can be useful to know for absolute pinpoint accuracy.

• Pixel and Subpixel
• Hex Angles

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

• Sonic
• Tails
• Knuckles

Collision

Solid Tiles
Terrain Part 1: A detailed description of the individual building blocks of terrain and how they are processed 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 its sensor arrangement to detect and react to sloped terrain.

• The Player's Sensors
• Sensor Activation
• Floor Sensors (A and B)
• Ceiling Sensors (C and D)
• Wall Sensors (E and F)

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, and 360° movement along extreme slopes such as walls and ceilings.

• 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

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