The code behind Quake's movement tricks explained (bunny-hopping, wall-running, and zig-zagging)

Summary

This video explores the evolution of player movement techniques in the Quake game series, highlighting three key techniques: zigzagging, wall running, and bunny hopping. These techniques, all stemming from a single piece of code, revolutionized gameplay and influenced the genre. The script delves into the mechanics, explains how players exploit the velocity update rule for speed boosts, and showcases advanced strategies used in tool-assisted speedruns for maximum efficiency.

Takeaways

• 😲 Quake's player movement techniques have evolved significantly over the years, impacting the way the game is played.
• 🔄 The earliest trick, zigzagging, involves rapid alternation of strafe keys while moving forward to gain speed.
• 🏃‍♂️ Wall running is performed by strafing into a wall while running parallel to it, another technique for boosting speed.
• 🐰 Bunny hopping or strafe jumping is a technique that has evolved and is used to maintain speed during gameplay.
• 🌐 All three movement techniques originate from the same piece of code, showcasing the game's influence on the genre.
• 🔑 The 'wishder' is a key concept, representing the player's intended movement direction, formed by combining forward and side vectors.
• 🔄 The player's velocity in the horizontal plane is updated based on the wishder, with vertical velocity calculated through a gravity model.
• 🔧 A loophole in the velocity calculation allows manipulation of the current speed, leading to the development of speed techniques.
• 📉 Friction affects speed, with different handling on the ground versus in the air, influencing how speed techniques are executed.
• 🛠️ Tool-assisted speedruns exploit these mechanics further, using scripting for inputs to achieve record times unattainable by human players.
• 👨‍💻 The video explains the original Quake source code and how it gives rise to these movement techniques, with references for further reading.

Q & A

How have player movement techniques in Quake evolved over the years?

Player movement techniques in Quake have evolved from simple tricks to elaborate routines, including zigzagging, wall running, and bunny hopping or strafe jumping, which have significantly changed the gameplay.

What is zigzagging in the context of Quake?

Zigzagging is an early trick in Quake where a player rapidly alternates the strafe keys while running forward to gain a speed boost.

What is wall running and how is it performed in Quake?

Wall running is performed by strafing into a wall while running parallel to it, allowing the player to maintain a constant wish-to-velocity angle and gain a speed boost.

What is bunny hopping or strafe jumping, and how has it evolved?

Bunny hopping or strafe jumping is a technique that involves holding a strafe key and turning the mouse to stay in an acceleration zone, and it has evolved to maximize speed in Quake.

How is the player's intended movement direction represented in Quake?

The player's intended movement direction is represented by a 'wishder', which is formed by adding a scaled forward vector to a scaled side vector and normalizing the result.

What is the role of the wishter in updating the player's velocity in Quake?

The wishter is used to update the player's velocity in the horizontal plane, while the vertical velocity is calculated according to a simple gravity model.

How does the velocity update function work when the player is on the ground in Quake?

When on the ground, the velocity update applies friction to scale the speed, and then updates the velocity by adding the wish scaled by an 'add speed' factor, which depends on the current speed and the maximum intended speed.

What loophole in the velocity calculation allows for speed manipulation in Quake?

The loophole lies in taking the current speed as the scalar projection of the velocity onto the wishter, rather than the length of the velocity vector, allowing players to manipulate the wishter relative to the velocity to make the current speed as large or small as desired.

How does zigzagging exploit the velocity update rule to increase speed in Quake?

Zigzagging gains speed by changing the strafe direction against the current movement direction, causing the velocity to move towards the wishter and then switching strafe direction to repeat the process.

What is the significance of the wish-to-velocity angle in strafe jumping?

In strafe jumping, the wish-to-velocity angle is kept close to 90 degrees by holding a strafe key and turning the mouse to stay in the zone of acceleration, allowing for continuous speed increase.

How does tool-assisted speedrunning in Quake differ from human speedrunning?

Tool-assisted speedrunning uses scripting of inputs to overcome human reaction and dexterity limitations, allowing for continuous selection of the wishter and alternate direction on every frame for maximum speed increase.

Outlines

00:00

🎮 Evolution of Player Movement in Quake

This paragraph discusses the evolution of player movement techniques in the game Quake, from simple tricks to complex routines that have transformed gameplay. It introduces three key movement techniques: zigzagging, wall running, and bunny hopping or strafe jumping. These techniques provide speed boosts and originate from the same piece of code, which has influenced many other first-person shooter games. The script explains the player physics logic, starting with the conversion of key presses and mouse movements into a 'wish der', which is used to update the player's velocity in the horizontal plane. The vertical velocity is calculated using a gravity model. The paragraph also delves into the mechanics of speed manipulation through the loophole in the velocity calculation, which is central to executing advanced movement techniques.

05:00

🔧 Exploiting Velocity Mechanics in Quake

The second paragraph delves deeper into how players exploit the velocity mechanics in Quake to achieve high-speed movement. It explains how techniques like zigzagging, strafe jumping, and wall running are executed, with a focus on the importance of the wish-to-velocity angle. The paragraph provides a detailed analysis of how these techniques are applied in the game, including the use of mouse movements and key presses to manipulate the wish der relative to the velocity for speed gains. It also touches on the use of tool-assisted speedruns, where scripting inputs allow for continuous selection of the wishter and maximize speed increases, resulting in record-breaking completion times. The video script concludes with an invitation for viewers to like, subscribe, and comment with any questions they may have.

Keywords

💡Zigzagging

Zigzagging is a movement technique in the game Quake where players rapidly alternate the strafe keys while running forward. It is one of the earliest tricks discovered and contributes to the speed boost in gameplay. As mentioned in the script, it involves changing the strafe direction against the current movement direction, causing the velocity to move towards the wish direction and pushing the player into a zone of deceleration, which is then followed by a strafe direction change to continue the speed gain cycle.

💡Wall Running

Wall Running is another movement technique in Quake where players strafe into a wall while running parallel to it. This technique allows players to maintain a constant wish to velocity angle by moving into the wall at a steady angle, providing a speed boost. The script explains that collisions with walls are handled by clipping the velocity to be parallel to the wall, which is crucial for the successful execution of wall running.

💡Bunny Hopping

Bunny Hopping, also known as strafe jumping, is a technique that has evolved over the history of Quake. It involves a series of jumps that minimize the time spent on the ground, thus reducing the impact of friction on the player's speed. The script describes how this technique is performed by holding a strafe key while turning the mouse to maintain the wish to velocity angle close to 90 degrees, which is essential for continuous acceleration.

💡Wish Vector

The wish vector, or wish direction, is a concept in Quake's player physics logic that represents the player's intended movement direction. It is formed by adding a scaled forward vector to a scaled side vector and then normalizing the result. The wish vector is crucial for updating the player's velocity in the horizontal plane, as it is used to calculate the speed changes during movement techniques like zigzagging and bunny hopping.

💡Velocity Update

Velocity update refers to the process of adjusting a player's speed in Quake based on their current movement and the wish vector. The script explains that when on the ground, velocity is updated by applying friction and then adding the wish vector scaled by a factor known as add speed. This process is key to understanding how movement techniques can exploit the game's physics to achieve higher speeds.

💡Strafe Jumping

Strafe Jumping is a technique that involves changing the view angle while holding forward and strafe keys to maintain the wish velocity angle in a 'sweet spot' for continuous acceleration. The script illustrates this by describing how players perform a pre-strafe or circle jump to gain initial speed before transitioning to the inner part of the jump, where the wish vector is manipulated to keep the player in a zone of acceleration.

💡Friction

Friction in the context of Quake's player movement is a force that opposes the player's speed, causing deceleration. The script mentions that when on the ground, friction is applied during the velocity update process, which affects how quickly a player can gain or lose speed. Minimizing the time spent on the ground is a strategy to reduce the impact of friction.

💡Acceleration Zone

The acceleration zone refers to the angle between the wish vector and the velocity where the player can gain speed. The script explains that to stay in this zone while strafe jumping, players must keep the wish to velocity angle close to 90 degrees, allowing for continuous acceleration despite the limitations imposed by the game's physics.

💡Tool-Assisted Speedruns

Tool-Assisted Speedruns are a type of speedrun that allows the use of scripts to input commands, overcoming human reaction and dexterity limitations. The script describes a world record run that completes the game significantly faster than any human record, achieved by using joystick-like inputs to continuously select the wish vector and maximize speed increases.

💡CL Forward Speed and CL Side Speed

CL Forward Speed and CL Side Speed are variables in Quake that adjust the length of the forward and side vectors in the wish direction. The script mentions that these variables can be used to fine-tune the player's movement speed and affect the execution of movement techniques such as zigzagging and strafe jumping.

Highlights

Quake's player movement techniques have evolved significantly over the years, impacting the game's playstyle.

Early tricks like zigzagging were discovered, involving rapid alternation of strafe keys while moving forward.

Wall running technique involves strafing into a wall while running parallel to it.

Bunny hopping or strafe jumping has seen its own evolution in the history of Quake.

All three movement techniques provide a speed boost to the player.

The techniques originate from the same short piece of code, influencing the design of many first-person shooters.

The player physics logic converts key presses and mouse movements into a wish vector for intended movement direction.

The wish vector is formed by adding scaled vectors and normalizing the result, influenced by directional keys and speed variables.

A loophole in the velocity calculation allows manipulation of the current speed, leading to speed boosts.

Zigzagging gains speed by alternating strafe direction against the current movement, demonstrated with slow motion analysis.

Strafe jumping involves a pre-strafe or circle jump to gain initial speed before空中 transitioning to the inner part of the jump.

Wall running is performed by running along a wall while strafing into it, with velocity clipped to be parallel to the wall.

In-air velocity update is similar to ground, with no friction and a reduced nominal maximum speed.

Strafe jumping requires keeping the wish-to-velocity angle close to 90 degrees for continuous acceleration.

Speed runners tap forward when approaching the ground to momentarily reduce the wish-to-velocity angle and maintain acceleration.

Tool-assisted speedruns exploit joystick-like inputs for continuous selection of the wish vector, maximizing speed increases.

The video explains different ways Quake's player movement and acceleration are exploited for speedrunning.

Transcripts

over the years quake's player movement

techniques have evolved from simple

tricks

through to elaborate routines that have

completely changed the way the game is

played

one of the earliest tricks discovered

was zigzagging a rapid alternation of

the strafe keys while running forward

next came wall running which is done by

strafing into a wall

while running parallel to it finally

there is bunny hopping or strafe jumping

a technique that has gone through its

own evolution over the history of quake

all three give the player a speed boost

and amazingly all three are born from

the same short piece of code

being the progenitor of a vast family of

first-person shooters

quake's player movement dna can be found

in many other games across the genre

for example any other game that features

strafe jumping of some kind

likely has the same short piece of code

or something very similar

at its heart we have explored strafe

jumping

specifically related to quake 3 in

another video linked here

in this video i'm going to dive into the

original quake source and explain how a

relatively small piece of code gives

rise to all three of these techniques

rather than showing the c code directly

i've translated it into pseudopython for

clarity

however i've also included references to

the c code if you wish

to read further the player physics logic

starts by converting key presses and

mouse movements into what's known as a

wish der

as the name suggests this gives the

player's intended movement direction

it's formed by adding a scaled forward

vector to a scaled side vector

and then normalizing the result which

components are included depends on the

directional keys that are being pressed

in addition the length of the forward

and side vectors can be adjusted with a

cl forward speed and cl side speed

variables

we'll come back to these later

the wishter is used to update the

player's velocity in the horizontal

plane

the vertical velocity is calculated

according to a simple gravity model

when on the ground the velocity update

looks like this

first of all some friction is applied

which scales the speed

the rest of the function updates the

velocity by adding on the wish to

scaled by some factor which i've called

add speed

the amount of speed to add depends on

the current speed and the developer

intended maximum speed

so far so good however it's in the

calculation of the current speed that

the loophole lies

rather than taking the current speed as

the length of the vowel vector it is

taken as the scalar projection of the

velocity onto the whisper

by using the keys and mouse to

manipulate the wish der relative to the

velocity

you can make current speed as large or

as small as you like

the add speed is then just the

difference of the current speed and the

nominal maximum speed

clipped to be between zero and a

constant intended to limit the player's

acceleration

whenever the add speed is being limited

by the max acceleration constant you can

make the speed on the next step faster

by bringing the whistler closer to the

velocity's angle

fully exploiting this bug then usually

requires having the current speed lag

behind the max speed by this

acceleration limit

let's see how this theory can be

exploited in the game with some slow

motion analysis of a few speed running

tricks

since the speed increase for a given

frame depends only on the wish angle

relative to the velocity

we can make a plot of hypothetical speed

increases

the blue bar here corresponds with the

selected wister

so the point where it crosses the curve

gives the actual speed increase

the technique shown here is known as

zigzagging which gains speed by changing

the strafe direction against the current

movement direction

the velocity then moves towards the

whistler pushing us into a zone of

deceleration

but then the player switches strafe

direction changing the whistler relative

to the movement direction once more

and so the process repeats with the

player gaining speed

until the speed gained by manipulating

the angle is balanced out by the speed

lost through friction

strafe jumps usually start with a move

on the ground where forward and a strafe

key are held while swinging the mouse

known as a pre-strafe or circle jump

this gains some initial speed before

transitioning to the inner part of the

jump

like zig zagging the whistler is

continually changed to keep the wished

velocity angle in the sweet spot

although this time it's done by changing

the view angle rather than the keys

here's an illustration of wall running

which is performed by running along a

wall while strafing into it

collisions with walls are handled by

clipping the velocity to be parallel to

the wall

this means that the wish to velocity

angle can be kept constant

simply by moving into the wall at a

steady angle as with the other

techniques

doing this at just the right angle gives

a speed boost note that when looking at

the wall

extra friction is applied so wall

running is best performed by strafing

into the wall

rather than running into the wall with

just the forward key

when in the air the velocity is updated

in a very similar way to on the ground

the only differences are that no

friction is applied and that the nominal

maximum speed is only 30 units a second

reducing the nominal maximum speed means

that to accelerate

the player's wish to velocity angle must

be close to 90 degrees

much less and current speed exceeds the

new limit and therefore add speed is set

to zero by the lower bound in the clip

call

much more and wish the points back on

vel enough that the total vector does

not get longer

when strafe jumping the angle is kept

close to 90 degrees by holding a strafe

key while turning the mouse to stay in

the zone of acceleration

to stay on a straight path the strafe

direction and turning direction can be

changed which places the angle near the

sweet spot on the opposing side

typically the player will chain together

a series of these jumps minimizing time

spent on the ground and subject to

friction

nevertheless there is still exactly one

frame between each jump when the ground

physics apply

this means that the acceleration zone

briefly moves to a more moderate angle

to deal with this the best speed runners

will tap forward when approaching the

ground

momentarily reducing the wish to

velocity angle

the exact angle is determined by the

ratio of the cl forward speed and cl

side speed variables

default values work pretty well provided

that the always run option isn't used

which doubles just the forward speed

instead the run key should be held or

plus speed issued at the console

which increases the forward speed and

side components in the same ratio

this covers all the ways that people

have exploited the velocity update rule

in quake

but is there another technique to move

faster it turns out there is

but it's only exploited in tool assisted

speedruns that is

speedruns that permits scripting of

inputs to overcome limitations of human

reactions and dexterity

here's a clip from the current tool

assisted world record which completes

the game in 9 minutes and 35 seconds

over 2 minutes faster than the human

record there's no side to side movement

as you'd normally see with strafe

jumping

yet nevertheless the player is still

gaining phenomenal speed

what's actually happening is joystick

like inputs are being used rather than

keyboard inputs

using inputs like this allows continuous

selection of the wishter

the script driving this run can then

select the wish to velocity angle on

each frame to maximize the speed

increase

being computer controlled the script can

alternate direction on every frame

resulting in a virtually straight path

unlike a regular strafe jump the view

remains stable as the mouse is no longer

required to influence the whistle

i hope this video has helped to explain

the different ways in which quake's play

or acceleration is exploited

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as always if you have any questions

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