Comments on: Game Physics http://gafferongames.com Glenn Fiedler, an Australian Game Developer in Los Angeles Mon, 15 Mar 2010 23:43:56 +0000 http://wordpress.com/ hourly 1 By: Glenn Fiedler http://gafferongames.com/game-physics/#comment-11918 Glenn Fiedler Thu, 12 Nov 2009 23:53:22 +0000 http://www.gaffer.org/game-physics/#comment-11918 it is generally necessary to renormalize the quaternion after you integrate it, provided that it is a certain distance from length 1.0, this may help. it is generally necessary to renormalize the quaternion after you integrate it, provided that it is a certain distance from length 1.0, this may help.

]]> By: dynamically challenged http://gafferongames.com/game-physics/#comment-11917 dynamically challenged Thu, 12 Nov 2009 23:50:18 +0000 http://www.gaffer.org/game-physics/#comment-11917 I'm trying to simulate simple drifting of an object in a water flow. So, I start with a stationary object and expect it to speed up and reach steady state at the same speed as the current. It seems to do this but after reaching steady state, an oscillation develops that eventually diverges. I noticed that after a couple uses of coordinate transformations using quaternions, some of the x,y forces bleed into the z axis (which is a no-no for my 3dof sim). Do I need to normalize occasionally or take some action to prevent angular momentum from being developed somehow? The cube demo seems to have an angular velocity damping term added to prevent this from being a problem.. is it necessary because of precision issues with the implementation? Thanks for the discussion. I’m trying to simulate simple drifting of an object in a water flow. So, I start with a stationary object and expect it to speed up and reach steady state at the same speed as the current. It seems to do this but after reaching steady state, an oscillation develops that eventually diverges. I noticed that after a couple uses of coordinate transformations using quaternions, some of the x,y forces bleed into the z axis (which is a no-no for my 3dof sim). Do I need to normalize occasionally or take some action to prevent angular momentum from being developed somehow? The cube demo seems to have an angular velocity damping term added to prevent this from being a problem.. is it necessary because of precision issues with the implementation? Thanks for the discussion.

]]> By: Glenn Fiedler http://gafferongames.com/game-physics/#comment-11913 Glenn Fiedler Thu, 12 Nov 2009 01:55:51 +0000 http://www.gaffer.org/game-physics/#comment-11913 I really cannot comment without knowing more details about your simulation, what exactly are you trying to do? I really cannot comment without knowing more details about your simulation, what exactly are you trying to do?

]]> By: dynamically challenged http://gafferongames.com/game-physics/#comment-11912 dynamically challenged Thu, 12 Nov 2009 01:03:07 +0000 http://www.gaffer.org/game-physics/#comment-11912 Thanks for being so generous with the source code AND dynamics simulation explanations. I've tried using your example code to model a real dynamic system and run into the dreaded divergence 'explosion'. Even though the dynamics are 'low' and the 100hz timestep should be plenty small enough (I think), it's not easy sorting out the cause.. Any suggestions for diagnosing this general type of problem? Is there a general series of diagnostic steps that you'd recommend for resolving divergence? (I started by cutting the timestep down by a factor of 10 but it just pushed the divergence further out in time). Since everything is done as a float is there a potential for things to become denormalized/inconsistent that requires frequent action? Thanks for being so generous with the source code AND dynamics simulation explanations. I’ve tried using your example code to model a real dynamic system and run into the dreaded divergence ‘explosion’. Even though the dynamics are ‘low’ and the 100hz timestep should be plenty small enough (I think), it’s not easy sorting out the cause.. Any suggestions for diagnosing this general type of problem? Is there a general series of diagnostic steps that you’d recommend for resolving divergence? (I started by cutting the timestep down by a factor of 10 but it just pushed the divergence further out in time). Since everything is done as a float is there a potential for things to become denormalized/inconsistent that requires frequent action?

]]> By: Glenn Fiedler http://gafferongames.com/game-physics/#comment-11812 Glenn Fiedler Thu, 15 Oct 2009 04:04:42 +0000 http://www.gaffer.org/game-physics/#comment-11812 it is fixed, thank you! it is fixed, thank you!

]]> By: scragar http://gafferongames.com/game-physics/#comment-11810 scragar Thu, 15 Oct 2009 00:51:50 +0000 http://www.gaffer.org/game-physics/#comment-11810 On the spring physics page there's a link tag around the text "next article" but it's not linked to anything. On the spring physics page there’s a link tag around the text “next article” but it’s not linked to anything.

]]> By: James http://gafferongames.com/game-physics/#comment-11806 James Mon, 12 Oct 2009 16:15:50 +0000 http://www.gaffer.org/game-physics/#comment-11806 Thanks Glenn, It looks pretty good. I'll give it a read, James Thanks Glenn, It looks pretty good. I’ll give it a read,

James

]]> By: Glenn Fiedler http://gafferongames.com/game-physics/#comment-11805 Glenn Fiedler Mon, 12 Oct 2009 01:59:54 +0000 http://www.gaffer.org/game-physics/#comment-11805 Hello James, well I was going to write one about collision detection, but then I found out about "Real Time Collision Detection" by Christer Ericson. This is *the* book you want to get. Any article I would write would just be inferior to this. cheers mate Hello James, well I was going to write one about collision detection, but then I found out about “Real Time Collision Detection” by Christer Ericson. This is *the* book you want to get. Any article I would write would just be inferior to this.

cheers mate

]]> By: James http://gafferongames.com/game-physics/#comment-11804 James Sun, 11 Oct 2009 13:46:23 +0000 http://www.gaffer.org/game-physics/#comment-11804 Hi Glen. I am loving the articles you've written so far. They're very informative and have given me some great ideas for building my own physics engine. I was wondering if you have any plans to write an article about collision detection (or if you've already written one). Thanks again! Hi Glen. I am loving the articles you’ve written so far. They’re very informative and have given me some great ideas for building my own physics engine. I was wondering if you have any plans to write an article about collision detection (or if you’ve already written one).

Thanks again!

]]> By: Glenn Fiedler http://gafferongames.com/game-physics/#comment-10515 Glenn Fiedler Sat, 28 Feb 2009 04:44:28 +0000 http://www.gaffer.org/game-physics/#comment-10515 i'm a self taught programmer, i have no degree but i've gone to a few university courses to brush up on some more mathematics - and i did advanced math in highschool, so i have decent background, but really *nothing* on somebody who went through actual physics or electrical engineering maths in otherwords, i have "programmer mathematics", meaning i learn what i need to do what i want to do, and not much more so i don't do calculus daily, just when i need it. and usually, it's very VERY slow :) but a key thing is that i always try to understand, as deep as i can what i am working on... so I do know the taylor's theorem basis for RK4 and understand it, and i can derive it if necessary. the only thing i'm a bit fuzzy on in the whole physics articles is how to calculate the spin quaternion to integrate the orientation from angular velocity. i don't fully understand the mathematics behind that, but the rest i'm pretty solid on. if you want to study something to get a deeper meaning of the physics equations, i highly recommend taking a look at baraff's siggraph courses on physics simulation (google for it) - this is a good place to get a good understanding of the mathematics and ideas behind physics simulation in fact really, you could just look at my articles as a poor man's version of his papers, covering much the same material, but with a programmer focus instead of a mathematics focus cheers i’m a self taught programmer, i have no degree but i’ve gone to a few university courses to brush up on some more mathematics – and i did advanced math in highschool, so i have decent background, but really *nothing* on somebody who went through actual physics or electrical engineering maths

in otherwords, i have “programmer mathematics”, meaning i learn what i need to do what i want to do, and not much more

so i don’t do calculus daily, just when i need it. and usually, it’s very VERY slow :)

but a key thing is that i always try to understand, as deep as i can what i am working on… so I do know the taylor’s theorem basis for RK4 and understand it, and i can derive it if necessary. the only thing i’m a bit fuzzy on in the whole physics articles is how to calculate the spin quaternion to integrate the orientation from angular velocity. i don’t fully understand the mathematics behind that, but the rest i’m pretty solid on.

if you want to study something to get a deeper meaning of the physics equations, i highly recommend taking a look at baraff’s siggraph courses on physics simulation (google for it) – this is a good place to get a good understanding of the mathematics and ideas behind physics simulation

in fact really, you could just look at my articles as a poor man’s version of his papers, covering much the same material, but with a programmer focus instead of a mathematics focus

cheers

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