Emitting particles one by one ... 2003-12-12 - By John Cassella
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Hey Gary,
use the positon of the center of your gun barrel geometry and the locator at
the end of the gun
barrel to derive the aim vector like this: (mind the word wrap)
//BEGIN MEL:
float $posLoc[] = `xform -q -ws -t locator1`;
float $posGun[] = `xform -q -ws -t gun`;
float $dir[] = {($posLoc[0] - $posGun[0]),($posLoc[1] - $posGun[1]),($posLoc[2]
- $posGun[2])} ;
vector $normalized = <<$dir[0], $dir[1], $dir[2]>>;
$normalized = `unit $normalized`;
//vector $velocityVector = $normalized; // this is your velocity vector !!!!
//now you can multiply the $velocityVector by a speed multuplier to make your
bullets go faster or
//slower or even add a little random speed by multiplying a small random
(rand(.01,.1)) against
//the velocity vector.
emit -object particle1
-position $posLoc[0] $posLoc[1] $posLoc[2]
-attribute velocity -vectorValue ($normalized.x) ($normalized.y) (
$normalized.z) ;
// END MEL
you normally need to feed the emit command a set of 3 floats to represent a
velocity vector
I convert the $dir value to a vector so I can normalize it and then multiply a
speed value to it
easier. but you could also just multiply your speed value by each of the 3
float array members and
use the normalize command on a set of 3 floats as well.
Hope this helps!
-john
garyc wrote:
> Hi John, right, I setup the "emit" command in my expression and it works
> just fine, I have taken the position data from a null that I have parented
> to the gun barrel, so I have the particles starting off in the right place.
> My only problem (well be it more a lack of knowledge) is how can I get a
> vector (i.e. a direction) for the particle when the barrel is moving around.
> Like I say I currently have a null parented to the barrel that gives me the
> position but I have the particle vector set to <0,0,50> so my particles
> always shoot off down "z" regardless of the guns orientation. Is there some
> way I can generate a correct vector from the same null that gives me my
> position, its "z" axis always (as its parented) points the right way, I just
> need that as a vector to plug into the emit command.
>
> PS: sorry if this is a no brainer questin for the maths guys out there, I am
> just trying to get my head around the maths thats goes with Maya ;)
>
> cheers gary.
>
>
>
>>Best bet is the "emit" command. set up an expression that gets the
>
> direction of the gun and
>
>>positon, for the velocity vector of the particle and muzzle position.
>>
>>then plug those numbers into the expression with the emit command to emit
>
> a particle
>
>>per frame.
>>
>>if you want more than one "shot" per frame (machine gun)
>>you can offset the position of the "bullets" up and down the velocity
>
> vector with some
>
>>random value. and loop on the emit command
>
>
>
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--
John Cassella (aka redpaw)
3d Animator
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redpaw@(protected)
direct line 323-308-3018
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"Where the heck is the ceiling?"
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