[ODE] questions regarding physically based camera modeling using ODE

[Jon Watte]

> Question 1: How do most games nowadays do it? Is the approach to generally 
> model the cameras as physical objects that the physics system controls? Or 
> is it usually one independant of a physics system. It seems to me like 
> physical modeling of the camera is the way to go since the gravity, and 
> collision detection stuff will be handled automatically, but it presents 
> other challenges...

I think it ranges all over. There calculates a desired position based 
on firing a bunch of rays from the desired subject (usually your avatar) 
and then picking the best, unobstructed view position; then a simple 
first-order filter pulls the camera towards the desired position. (There 
is a preference towards not moving the camera if possible)

In some stuff I'm experimenting with (based on ODE), I model the camera 
as a sphere with a radius that's about 1.5x the near clipping plane 
distance. That way, it doesn't clip through geometry, which is always 
nice :-) The problem is that you get all the kinds of problems that you 
will get with an integrator system: fishtailing, bobbing, springy 
response, and all that. If you make it too stiff, you get vibration or 
possible explosion.

I actually let the sphere rotate freely, and place the camera in the 
center of the sphere, but orient it according to a desired up vector and 
desired look-at target, rather than trying to use the sphere's 
orientation.

> Question 3: If I go with physical modeling, how does this tie in with 
> multiplayer support? the problem is If I allow the physics system to control 
> camera movement and collision response, what data do I send to the networked 
> players in the game, and extrapolate expected positions using a curve fit?  
> This puzzles me....

I use the category/collision bits to mark the camera as something that 
collides against other things, but doesn't affect other things. I e, 
when the camera collides with something, I attach the contact joint to 
the static environment and the camera; the other object is unaffected.

> Question 4: Pardon my ignorance, but what is an inertial tensor? I have a 
> feeling this has something to do with question 2 mentioned above...

An inertial tensor is a representation of how mass is distributed around 
the center of gravity of some object. It's what gives you the ability to 
wobble, and then to settle around one of the three main axes for a block, 
but a sphere will just spin smoothly wherever it's spinning.

Once you know vectors and matrices (basic linear algebra), tensor calculus 
is a logical progression from there.

Cheers,

			/ h+