Objects react to collision? (Wishlist)

Objects react to collision? // Wishlist

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Jan 15, 2005, 1:36am
I was wondering if it was possible to have a command to have some objects re
act to being touch/hit by another object, the best example would be a soccer

I'm not sure how it would work.. But if it was just for the one person to
see (much like the activate move command), it shouldnt be all that hard. If
it was to be done and show everyone, it would be quite harder, I would

I think for few reasons, it should be a seperate special command itself, so
people cannot misuse and abuse it in worlds like AW.


Jan 15, 2005, 5:53pm
[View Quote] I think the bump trigger only works when the object is touched by an
avatar. To get an object to react to another object's touch, you might
try a chain of animate (as a timer) action commands. There's an example
of chained sign commands in AW at 20007N 7779E 270 (the scrolling sign).

> If
> it was to be done and show everyone, it would be quite harder, I would
> imagine.

I think a bot could do that, even if only by creating the reaction on
the fly.


Jan 15, 2005, 6:05pm
It would be nice if objects can use something like an If.. Then command like
in BASIC. For example: If tree8m.rwx = 15w 10n Then tree4m.rwx move 10 10 0
and you can have it so you can use any command besides move.
You can also made a new command called collide or something and have: If
tree8m.rwx collides with tree4m.rwx radius = .5 then ..... radius would
be the area around each object in coordinates, that would need to get into
range to set off the If / Then command.


[View Quote]


Jan 15, 2005, 8:16pm
Opps.. I was meaning an object being hit by an avatar.
My bad.

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Jan 16, 2005, 12:39am
[View Quote] np. Well, then the bump trigger could at least initiate the process.

I'm unauthorised to use "move" in AW so I haven't played with it.
The help at http://www.activeworlds.com/help/aw36/move_command.html
says it "causes an object to move ... and then back again." It wouldn't
seem natural for a soccer ball to bounce back to where it was kicked.
No dice there.

This is an interesting problem though. It might be generalised to
avatars striking any object, like a cue ball or a baseball. Dreaming
now ... a bot could find the angle of approach of the avatar with an
arctangent function and even its velocity of approach with the
AW_AVATAR_Z/delta time) and then recreate the soccerball at its
projected landing point using sine and cosine of the aforementioned
approach angle multiplied by the impact velocity. (Lather, rinse,
repeat, accordingly.)

This seems an architype for other ball games. Has this been done
already? Maybe in that bowling game?

(I'm new here, haven't bowled yet. Sorry if this is too geeky.)

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Jan 16, 2005, 5:28am
Nothing is too geeky. The more knowledge, the better.


Jan 16, 2005, 6:31pm
Just for kicks I made an object/object collision anyway. It switches
visibility off and on instead of using the move command.

If anyone's curious, it's in AW at 20019.5N 7778E 90 . Click the green
cylinder and it knocks the red cylinder away.

I understand this doesn't resolve the original wish for an
avatar-kick-object command but maybe this will help someone else peeking
in on this thread. :-)

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sw chris

Jan 17, 2005, 8:04pm
Sounds to me like AW should license the Half-Life 2 engine. :D


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Jan 20, 2005, 3:53am
No, you're not.

[View Quote] > I'm unauthorised to use "move" in AW


Jan 28, 2005, 3:33am
Okay, well, basically if you want reactive physics entities you have to
write some physics code and then link it to a bot's position in-world. The
hardest part is that you're going to have to write the terrain, avatar, and
object collision code for this object and know enough about the math and
such to create at least semi-realistic reactions. Also, the object won't be
able to roll very realistically in all directions since pitch only goes
from -90 (facing up?!) to 90 (yes, facing down) degrees.

My suggestion is that objects and avatars be treated as their bounding boxes
(get this info from the registry), as writing a full per-triangle collision
engine is not so easy (if it was, AWI might get around to refining the one
in the browser a bit). Doing terrain collision is easy (I've got that code
around here somewhere if anyone wants it, though it's really only useful as
a "how to" since it relies on my PGC's internal data structures).

Once you've got your collision code you encapsulate it, forget about it, and
set up a simple method to handle collision events. Depending on the types
and masses of objects involved, create the appropriate reaction forces.

I'll get you started.

physEngine.collisionScan(); // execute the function that checks if any
objects are colliding with other objects here. 20 frames per second.

Sorry, I have delusions of being witty, but anyway, it's not exactly a
simple task if you want it to be realistic. If you want it to be only
semi-realistic, then things are a little easier. Instead of writing a
collision engine for all the objects, you could just use a distance check;
if the ball is within 1m or so of an avatar or another ball it's considered
to be in contact with it. Combine that with the terrain collision engine and
you have a working system for playing soccer on terrain. Getting a little
fancier, you could optionally set certain physics objects to stay only
within a certain area (for example, the soccer ball hits an invisible wall
if it tries to leave the defined soccer field area). You might then also
want to place some collision beacons which link to specific scriptable
events; in this case, goals.

If you want realism without effort, you could pick up an open source physics
engine (ODE I think it's called?) and link that up to your bot, though I
don't know how hard that would be (probably rather hard).

Suffice it to say, this *can* be done (it's much like those silly
manually-flyable plane bots I had in Proxima), but it's really a task for an
at least semi-experienced programmer. In order to actually be a playable
game, server->bot lag would have to be removed by having both on one PC, and
the avatar updates would have to be increased for more accuracy in collision
detection (a little bot-side movement prediction a la most multiplayer games
would also help here, and is easy to do; until new data has arrived from the
server, assume the player is still moving at the same velocity it was).

And there we have the physics in AW issue. If there's really interest in a
little physics model bot to play with I might think about tossing something
simple together and putting it up as open source, but it all depends on 1)
interest, 2) has it been done already? and 3) my time constraints. If anyone
cares, let me know and I might put together a soccer ball bot demo or


[View Quote]


Jan 29, 2005, 3:04pm
Fascinating stuff. Imagine orbiting bodies like a twin star or a
star-planet system. Crash your avatar into it, perturbing it, then you
can stand back and watch the whole mess restabilize into new orbits!

Also, virtual artillery! lol

[View Quote]


Feb 28, 2005, 12:46am
At AW 20017N 7784E there's a curious example of one object appearing to
react to another which in turn reacts to the one. It's a pneumatic
oscillator that could be manufactured in the real world. (If you spot
the possible problem of a piston port connecting the wrong pressure
lines, consider it could be solved by shifting the depth of alternate

[View Quote]

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