Lagging and glitching

This guide aims to provide an overview of what we know now about lagging and glitching the game. First some definitions:
* **Lagging** means making the game stop processing for a duration of time. Most commonly done by pressing S or PrintScreen on the keyboard. There are other methods, however, like dragging the game window around
* **Glitching** refers to making the game behave in an unintended way. Lagging can be used to do this

# Currently known glitches:
1. Superjump
2. In-game timer manipulation
3. Tree warp

## Superjump
The oldest known glitch, found in 2016 by Nimanao. It allows you to jump a lot higher than normally possible. Demonstration: https://youtu.be/Sk4jJM279Fw (instructions in the video description)

## In-game timer manipulation
This glitch makes the game display a lower end time than is accurate. Previously known as a side effect of the superjump, Galanga used it without the jump to set a 0.02s time on Bunny Hill in December 2020. Demonstration: https://youtu.be/Gx5C70SDEzc (instructions in the video description)

## Tree warp
Found in February 2021 by TripleBuffered, this glitch allows you to warp through trees at the side level boundaries. Demonstration: https://youtu.be/mJdY0OpfsEk (instructions in the video description)

# Why does lagging cause these glitches?
The game has a main loop that processes keyboard input, calculates game physics (Tux's movement) and draws the results to your screen every frame the game runs. Normally, this happens 60 times a second. However, when you lag the game, this loop stops processing for a while. Once it resumes, all missed input is processed, then all the physics calculations for the missed time are done in one go, and then the final result of that is drawn to your screen.

The glitches are caused by differences in the physics calculations. For the most part, these calculations don't change much when the game is lagged, as the game's ODE solver will just chop up the long duration in small timesteps and process each of those in turn. Collision detection, terrain type and slope processing, force calculations and so on still happen normally. However, there are two important actions that are only done once per frame, no matter how long lagging has made that frame:
1. Updating game time
2. Clipping Tux back in bounds

## Updating game time
Game time (the time that has passed since the current race started) is stored in the global variable *g_game.time*. It is updated once per frame, after all the physics calculations are done. This means that any calculation that depends on game time will give different results when a frame is lagged. And that, in turn, causes the superjump. When jumping, the game applies an upward force to the character for a short duration of time. To check if that time duration is over, game time is used. So if the game time falls in that duration at the start of the lagged frame, the upward force will be applied during the entire length of the frame, no matter how long that frame is.

Additionally, game time is not updated if the global variable *g_game.finish* is true. On certain levels, this variable is set to *true* if the physics calculations detect that the finish line barrier was crossed. If that happens on a lagged frame, the game time will keep the value that was set at the end of the previous frame, which may be a long time ago. This causes the in-game timer manipulation glitch. Levels on which this is possible: Bunny Hill, Twisty Slope, Bumpy Ride and Frozen River.

## Clipping Tux back in bounds
The physics calculations make sure Tux is clipped back in bounds if he is out of bounds, but they only do so once each frame, after the ODE solver has finished processing. While the ODE solver is processing Tux's movement in small timesteps, his position can be out of bounds. This causes the tree warp glitch. If you create enough lag to give Tux time to pass the tree(s) out of bounds before he is clipped back in, there will be no collision and no speed loss.

# Glitchcam
In March 2021, TripleBuffered modified the game code to add a glitchcam. This way, you can see the physics calculation steps the game does when recovering from lag, and you can see the glitches happening.

## Superjump
https://youtu.be/_k7RcNdhKZs

## In-game timer manipulation
https://youtu.be/rLa9ZZcPFJs

## Tree warp
https://youtu.be/BD6-Ph5S0g8

Movement Basics

1) Make sure to start paddling (Up arrow key) right after the race starts. Note that starting the race "eats" your input, so if you press Up while Tux is walking toward the line, he will not paddle until you release Up and press it again. I solve this by pressing Enter to start the race, then immediately pressing Up

2) Zigzagging helps you accelerate faster, especially at the start. It's a rhythm to learn, but it can easily save 2 seconds. Just press Left-Right-Left-Right-Left-Right and so on, try to do it in such a way that you keep going in the same overall direction.
The top records on Frozen Lakes Any% No Game Lag ( https://www.speedrun.com/extreme_tux_racer/Frozen_Lakes#Any_No_Game_Lag ) show very effective zigzagging at the start. Notice how they reach 60 km/h in 4.x or 5.x seconds. Without zigzagging, it takes well over 7 seconds to reach 60 km/h

3) Make sure to stop paddling once you reach 60 km/h. Above that speed, paddling only slows you down

4) Building and preserving speed is generally more important than tight lines, because acceleration is very slow. You accelerate much faster on ice, so try to hit ice patches if they're not too hard to include in your route. Avoid or mitigate route parts that lose a lot of speed

5) Pressing the Up arrow key while airborne will make Tux flap, which makes you fall down a bit slower and allows you a tiny bit of air steering with Left and Right. If your keyboard allows it, you can gain sharper air steering by pressing Up + Down + (Left or Right)

Update 2021-12-07:
- Updated the link to examples of zigzagging
- Added a sentence about sharper air steering
- Removed the sentence about the guide probably needing updates in the future :)

Slow down skip

If you hit a tree your speed decreases to almost 0 and if you hit it at the end of the stage when you lose control, you don't have to wait until the penguin slows down and you can select the next stage.
This can be achieved easily if you jump to the tree because the penguin will rotate to the center of the finish if you don't.
This can save up to 2 seconds per stage.

[A demonstration using this technique](https://www.youtube.com/watch?v=SdAbnnunrcM)

Super Jump Glitch

To do this, hold down spacebar and once it's fully charged, release spacebar and quickly tap s.
The screen freezing before the jump isn't a recording error, the game actually does that (because default "S" button serves to screenshots)

Capuno

kompowiec2

TripleBuffered

Extreme Tux Racer

Bunny Hill

Twisty Slope

Inception

Rock'n'Roll

Wild West Chute Out

Teromate

ReedSpun

EUR / PAL

Not Mirrored

Mirror

Mirrored

Linux

Full-Game Runs and Sound 22-07-2021

Rules Clarification 15/02/2021

"Who says penguins can't fly" as a new category.

Mutual discord

Resetting progress

pomelux

SixRock

InstaSim

VictorianKestrel

planckcons

名称	作者
Lagging and glitching	TripleBuffered 4 years ago
Movement Basics	TripleBuffered 3 years ago
Slow down skip	Capuno 6 years ago
Super Jump Glitch	kompowiec2 7 years ago