[ODE] Simple character control

[Megan Fox]

> > And an addenum... what about animation?
>
> You're note setposition-ing anything in ODE; you're extracting
> position to determine where to draw the mesh.
>
> Note that animation is totally different from simulation in most
> games. You animate by using a high-resolution character skeleton,
> but you usually don't simulate that entire skeleton. Instead, you
> measure how far you've traveled across ground since last frame,
> and advance the walk cycle by that much; this avoids foot sliding
> on even ground; the IK takes care of the uneven ground case.
>
> The extreme end of realism would be to simulate the skeleton as a
> rag doll, with forces applied to the joints to create the walk
> cycle. However, that doesn't qualify as "simple" at all :-)

If you separate animation data from collision data, you seemingly open
yourself to any number of inconsistent interactions.  Player sphere is too
big, so the player can't actually "touch" the wall, player sphere is too
small, so the player's arm can clip through the wall if the animation is at
the wrong point at the time, player's tall hat clips through a low archway
because it isn't physically modelled, player's long staff weapon clips
through a wall (and 3 cups on a table) during attack, etc.


On the other hand, a ragdoll-modelled character mesh being keyframe animated
seemingly gives you properly accurate collision regardless of animation
frame, will always generate the contact data you need to adjust the
animation (if an arm is hitting the wall, stop the animation or similar),
assures proper physical response regardless of player's stance or animation
(a character's pointing arm knocks the cup off the table in front of her),
etc.  It even gives you "damage zones" - if an object collides with the
player at high speed, you can decide what effect it has based on the body
part it hits.


I see that the docs suggest not using setposition and setorientation... but
why?  It seems absolutely ideal for when you want the entity's movement
assertive over the environment, and it should be fairly easy to handle the
contact joints yourself to resolve collisions (and enable ragdoll if the
forces get too high, or whatever).  Is the only reason that many won't pay
attention to the contact joints, and the general instability you get from
warping objects inside other objects (only a big problem if your step size
is too large)?


-Megan Fox