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

Basics

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

• Positions
• Angles
• Variables

Characters

Information about specific characters and their constants, variables, their varying sizes and jump height, and also detailing how their specific moves work.

• Sonic

• Drop Dash
• Super Peel Out
• Insta-Shield

• Tails

• Flying

• Knuckles

• Gliding
• Climbing

Collision

Solid Tiles

A detailed description of how sloped terrain is constructed and detected.

• Sensors

Slope Collision

Slopes Part 1: How the Player object uses its sensor arrangement to detect and react to Solid Tiles and slopes.

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

Solid Objects

Object hitboxes, the Player's hitbox, object solidity, platforms, and other ways objects directly interact with other objects.

• Object Hitboxes
• Solid Objects
• Sloped Objects
• Jump Through Platforms
• Pushable Blocks

Physics

Slope Physics

Slopes Part 2: How the Player moves with momentum over angled surfaces, and collides with extreme slopes such as walls and ceilings.

• Moving At Angles
• Switching Mode
• Falling and Slipping Down Slopes
• Landing On The Ground

Air State

Horizontal input & general physics of the Player while they are in the air.

Running

Horizontal input & general physics of the Player while walking/running.

Jumping

Jump physics, jumping at angles, and how controllable jump height is achieved.

Rolling

Horizontal input & general physics of the Player while rolling.

Getting Hit

What happens when the Player gets hit.

Rebound

The Player's physics bouncing off enemies and other destroy-able items.

Underwater

The Player's physics underwater.

Super Speeds

The Player's 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 elemental shields.

• Spindash
• Shield Abilities

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