SPG:Underwater

Sonic Physics Guide
Basics Positions And Speeds Angles Variables Calculations (Technical) Pixel and Subpixel Hex Angles Characters Sonic Tails Knuckles
Collision
Solid Tiles (Terrain Part 1) Sensors Solid Terrain (Terrain Part 2) Layers Loops Slope Collision (Slopes Part 1) The Player's Sensors While Grounded 360 Degree Collision While Airborne Hitboxes The Player's Hitbox Trigger Areas Solid Objects Solid Objects Sloped Objects Jump Through Platforms Pushable Blocks Item Monitor
Physics
Slope Physics (Slopes Part 2) Moving Along Slopes 360 Degree Movement Falling and Slipping Down Slopes Landing On The Ground Air State Running Jumping Rolling Getting Hit Rebound Underwater Air Physics Super Speeds
Gameplay
Main Game Loop Game Objects Game Enemies Badniks Bosses Ring Loss Special Abilities Spindash Super Peel Out Drop Dash Insta-Shield Flying Gliding Climbing Elemental Shields Flame Shield Bubble Shield Lightning Shield Player 2 Player 2 CPU Respawning Special Stages Rotating Maze
Presentation
Camera Animations Animation System Variable Speed Animation Timings Normal Animation Timings Animation Rules
Special
Overlay Scripts Sonic 1 Overlay Sonic 2 Overlay

Notes:

• The research applies to all four of the Sega Mega Drive games and Sonic CD.
• When Sonic is underwater he moves much more slowly, but otherwise his physics are largely the same. This is achieved mostly by halving the pertinent variables, but some, like gravity and initial jump velocity, are not exactly half.

Underwater Constants

 acceleration_speed: 0.0234375 (half of 0.046875)
 deceleration_speed: 0.25 (half of 0.5)
 friction_speed:  0.0234375 (half of 0.046875)
 top_speed: 3 (half of 6)
 
 air_acceleration_speed:  0.046875 (half of 0.09375)
 
 roll_friction_speed: 0.01171875 (half of 0.0234375)
 roll_deceleration_speed: 0.125 (unchanged)

 gravity_force: 0.0625 (instead of 0.21875)
 jump_force: 3.5  (3 for knuckles) (instead of 6.5  (6 for knuckles))
 jump_release: -2 (instead of -4)

Getting Hit

When getting hit underwater, the Player will fly back with an X Speed of 1 (or -1) and a Y Speed of -2, half that of normal.

Bubbles

When the Player gets a bubble underwater, their X Speed and Y Speed are both set to 0.

Entry & Exit

When the Player enters the water, their X Speed is multiplied by 0.5 and their Y Speed is multiplied by 0.25 (this occurs after gravity_force is added to Y Speed). Conversely, when the Player exits the water, their Y Speed is doubled (after water gravity_force has been added), (however, X Speed is not affected when leaving the water).

Drowning

When the Player drowns, their X Speed and Y Speed are both set to 0, and the gravity_force remains set to the lower water gravity.

Speed Shoes

When in possession of Speed Shoes, but also underwater, the underwater variables take over, effectively nullifying the Speed Shoes altogether. No calculations, such as multiplying by 0.5, take place.

Animation Speeds

Being submerged doesn't affect the speed of the Player's animations at all. Variable Speed Animations will be attenuated by the same proportion automatically.