• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Waterlimon

How would i implement friction?

9 posts in this topic

Im trying to add friction to my physics engine.

 

I know:

 

-The collision point and normal

-Properties of both bodies:

*Center of mass

*mass, inertia

*angular and linear velocity

*angular and linear forces

 

So, how would i go about implementing friction?

 

Currently i am able to apply a force to a point on a body (which translates to linear force and torque)

 

I am able to do friction for surface on surface (its a top down 2d game) where i assume the other surface to have infinite mass. However this directly modifies the velocity and im not sure how to translate that to friction from collisions.

 

The internet didnt seem very helpful on this one, anyone care to explain how to make it all work? Preferably in a way that works smoothly and wont estimate the forces wrong and cause everything to explode.

 

I tried to use my getDeltaVelocityCuzOfFriction(VelocityDifference, frictionCoeff, normalForce) method but since i dont have a method of setting force directly at a point on the body, and i dont know how to get the normal force, i couldnt get it to work. There might be other problems with my collision response that cause it to not work but i cant be sure until i know the friction itself should work.

 

Thanks.

0

Share this post


Link to post
Share on other sites

Every game tick I'd bring the velocity closer to zero.   Then have different reduction values for not touching the ground and touching it.

 

I'd probably ignore everything else like inertia, would probably even ignore how friction changes with speed(it doesn't but you're covering more distance).    To get things like terminal velocity if I needed it I would probably just "word of god" say you won't go faster than X speed.

 

EDIT:  A Lot of programmers even cheat a lot worse and just use look up tables for where a character should be in a jump in some cases.

______

 

It actually makes a lot sense why the Internet isn't being helpful to you.   Physics equations have all those exponents to keep track of totals/positions.   However you the programmer are already keeping track of the those totals by always knowing the exact position of your character at all times(well most times, and depending).

 

So if you want the 100% right and correct answer you should go looking for the derivatives of the physics equations you're looking at.

Edited by lithos
0

Share this post


Link to post
Share on other sites

I cant simplify it much since this isnt a platformer - there are no static parts.

 

I will make a "set velocity at point x" method and work with velocity instead of forces because that seemed to work for the simpler case.

 

I still need to find out how to find force of contact (ignoring gravity) and how to make it so that if a big and small object have friction between them, the big one wont move as much as the small one... hm.

0

Share this post


Link to post
Share on other sites


I still need to find out how to find force of contact (ignoring gravity) and how to make it so that if a big and small object have friction between them, the big one wont move as much as the small one... hm.

 

that's impulse and momentum and conservation of momentum, not friction. 1st year mechanics. any decent college physics book will have the info.

 

as i recall, m1*v1+m2*v2 (inital - before collision) = m1*v1+m2*v2 (final - after collision).   or something like that, better look it up.  <g>.

 

friction is a totally different set of physics formulas. 

 

with friction, the variables are mass, velocity (? been a long time), and Ks or Kd, the coefficient of static or dynamic friction, depending on whether you're sliding/skidding (dynamic) or not (static). Ks and Kd are constants that are empirically derived for two given surfaces (such as tire rubber and asphalt, ice on ice [which is about the lowest], etc).  the exact values of Ks and Kd are different for any 2 given surfaces.  but they all follow the general rule that Ks is higher than Kd (or is it always lower? <g> another one you'dd better look up). Ks and Kd essentially define the points at which you lose and regain traction, based on the speed, vehicle weight, and the type of friction surfaces.

0

Share this post


Link to post
Share on other sites
I got dynamic friction working now (seems to)

But how to implement clamping so it won't jitter ?

It seems like a rather complicated problem. I can see it being possible with 2 bodies and some lengthy calculations with inertia and all, but for more bodies i think i need one of those "solver" things physics engines are full of. Any advice?
0

Share this post


Link to post
Share on other sites

as i recall, m1*v1+m2*v2 (inital - before collision) = m1*v1+m2*v2 (final - after collision).   or something like that, better look it up.  <g>.


More or less correct. This is the conservation of momentum. The force (which is what you're calculating there) is equivalent, and gets split evenly between the colliding bodies. Calling it before and after, it should be specified that the body with larger mass will undergo the smaller acceleration.

This is essential Newtonian physics.

F = ma (force equals mass times acceleration)

Combined with the Third Law (opposite and equal reaction), you locate the point of impact, multiply the mass of each body by its acceleration (just it's velocity vector, in non-relative terms). Sum the vectors, then divide the resulting vector by 2 and apply it as a force against the objects, away from the point of impact. Remember that when applying the force F = ma applies in reverse, so you divide the force amount by the mass of the object and then just add the resulting vector to the object's existing acceleration. Edited by Khatharr
0

Share this post


Link to post
Share on other sites

I have that part correct, friction should work correctly at relatively high tangential (?) velocities.

 

However, the problem is, that at low velocities the fricition froce will be too high which causes it to reverse the direction of the tangential velocity which causes jitter, and at high velocities, more serious unstability.

 

As i understand it i need to find the force that would reverse the direction of the velocity and clamp the friction impulse to that (so if the impulse is too high, itll just zero out the relative tangential velocity instead of reversing its direction)

 

I just need some guidance as to how to find that maximum impulse, preferrably something that also works in multiple body systems (some kind of iterative solver thingie?)

 

I will attempt to find the maximum impulse for a single contact (ignoring multiple simultaneous contacts)

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0