a strange thought

As I sit here at my desk at work too annoyed to do anything productive, yet too bored to do other wise it struck me how odd it is what I do. I have my development studio open  (yes visual studio, YUK) I realize that I have a code window open that is split in two with a break point across each pane,  book mark and a disabled break point. I just imagined that to a person not used to programming that this mess would be complete gibberish. Yet I am completely at home, completely familiar with the mess. The split screen actually make it easier to do my job while at the same time makes the screen resemble a cockpit from a 747 with too much going on to pay attention to.

I <3 what I do

I <3 who I am

and yes, I am a geek :D

Integrator blues

So, here I am working on the Drive train for Rigs of rods and I've got a conundrum. My typical approach to forces and integrators is that when you add a force to an object you expect it to last for the size of the time step, any longer and what ever added the force needs to keep adding it. Perhaps I should still keep to that principle.

Here is my problem, I want to hide the integration stops from anything interacting with the integrator. This comes to be a problem (for me anyways) when getting into higher order integrators such as the Runga-Kutta K4 (4th order). It seams that any integrator higher than 1st order requires steps smaller than the given time step, for example, RK4 takes 3 extra euler steps for every integrator step, it takes two steps at half the time step, and one at the full time step.

lets setup an example:

class object {
    float force;
    float x;
    float v;
public: 
    //! apply constant force for the next integration step
    object() : force(0.0f), x(0.0f), v(0.0f) {}
    void applyForce(force(float force) { this->force += force; }
    void integrate(float dt) {
        x += v*dt;
        v += force*dt;
        force =0.0f;
    }
};

so say you have two of these objects coupled together by a spring (f = -kx) now RK4 is basically

1. Get derivative @ t=0, k1
2. Advance dt/2s using k1, get derivative k2
3. Advance dt/2s using k2, get derivative k3
4. Advance dts using k3
5. Advance dts using a weighted average of the difference derivatives (k1 + 2*k2 + 2*k3 + k4)/6

Notice 2 half steps and 1 full step. When dealing with multiple bodies you can't run through steps 1-5 for each object, you need to do step 1 for all objects, steps 2 for all objects, etc.

Lets say you have a sim of with a time step of 0.001s, you have an external system that adds 100N to the object. the 100N is to be applied for 0.001s while the force from the spring needs to last for 0.0005s, then is recalculated again.

Perhaps, forces need to be distinguished between static forces and dynamic forces. Static forces are forces that depend on user input, for example a car engine, mouse movement, etc. Dynamic forces are the internal forces generated by the physics simulation. In other words Static forces are applied and last an entire time step, dynamic forces are calculated on the fly when requested.


Hmm, while typing thing I wonder an approach similiar to Ogre frame listener would be appropriate. calsses that effect an object can be registered as a "FrameListener" of sorts, there are calls to each listener that signal the start of the tiem step calculation, and one at the end of the calculations, and perhaps each intermediate time step when using higher order integrators.

Food for thought, but perhaps at a later time.

New years resolution

I don't have many ambitions but this year I have decided there are a few things I want to do

1. go on 12 MTB rides with the BOMB group
2. Finish the Samurai
3. Do the long run every morning when I walk the dog
4. Upgrade the electrical in our house, includes put the bedrooms on seperate circuits, and a 230V to the garage.

Thats all!

Holy crap, two posts!!

That's a record.

The previously posted video really got me thinking about you tube and it's importance, I have since watched the Larry Lessig TED talk:

We have to recognize [that children are] different from us. We made mixed tapes; they remix music. We watched TV; they make TV.

It is technology that has made them different, and as we see what this technology can do we need to recognize you can't kill the instinct the technology produces; we can only criminalize it. We can't stop our kids from using it; we can only drive it underground. We can't make our kids passive again; we can only make them, quote, "pirates." And is that good? We live in this weird time, it's kind of age of prohibitions, where in many areas of our life, we live life constantly against the law. Ordinary people live life against the law, and that's what I -- we -- are doing to our kids. They live life knowing they live it against the law. That realization is extraordinarily corrosive, extraordinarily corrupting. And in a democracy we ought to be able to do better. Do better, at least for them, if not for opening for business.

Talk about a profound point, one I could not agree with more. the entire making TV part is the entire point of youtube, without youtube, or similiar sites we can't make TV or remixes and all of what Larry Lessig is talking about is pointless. Sure, remixing and making TV is nothing the internet has created. Every one made home video but they stayed in the home, you tube allows them to be published to the world, allows every one to view them, that is the only real difference. Before you had to go go some where to watch or get the media, you could never share media in the same way you watch TV. Now you turn on an electronic device and start surfing youtube.

But different from legal reason there are other reason to be concerned with keeping sites like youtube alive and healthy. Oddly, it's research:



It is likely no one has heard of this person before he released this video, now he has almost 3,000,000 views and has doen a TED talk. Watch the video it speaks world more than I could, and the important part is that you has allowed him to speak out and be heard.



All in all it is simply amazing, and I fear I've taken it for granted and/or treated what I have as trivial. It takes a while to realize how important this technology is.

A Start

I watched some interesting videos tonight that made me think about my "Online" presence. I am very much an on-line person, yet at the same time not. I guess it would be more appropriate to to say I'm a pseudo techy person that limits his online social activity. After all on-line interaction isn't the same as offline interaction.

Well so start this video got me thinking:

I realize I really don't have much to add, in fact my whole opinion of [vb]logging is these people aren't so important that people will read their [vb]log. After watching that Video I more realized, it's not about the [vb]logger giving something to their audience, but rather a place to "throwup" on a page and clear your head. Get your thoughts out and move on. Well bed time, maybe later.