Maya 2020 fundamentals - modelling the real world
Get halfway through a model and find it's an unworkable mess? Can't add edge loops where you need them? Can't subdivide a mesh properly? If any of this sounds familiar check this course out.
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1
14-07-2004
, 11:23 PM
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Join Date: Feb 2003
Join Date: Feb 2003
Location: Los Angeles
Posts: 695
rain splotches
I have this rain falling in a canyon and the camera is a crane shot. Now the canyon is actually made out of a light colored sand, so when the rain hits, besides little splashes I want to have the sand get darker in those spots. I've got it working that on the collision event, and particle with an instanced object is created it that spot with no movement, and I plan to get it looking right in the composite. This part all works fine.
Here's where I'm stuck. The little instanced planes are always pointing up. This would work well if the canyon were flat, but it's not. When a rain drop hits the walls, the splotch still points up rather than having the appropriate perspective. What I think I need to do is figure out a way to read the tangent at which the drop hit the wall, and the set the aim direction of the instanced particle to be perpendicular to it. This is the part I have no idea how to do.
My guess is no one here will know either, but I figured it was worth a shot.
Thanks,
-dann
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2
15-07-2004
, 12:27 PM
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Location: London, UK
Posts: 2,800
I'll get back to you when I figure it out. i know what to do but I can't get the info I need back from maya at the moment.Alan
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3
15-07-2004
, 06:40 PM
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4
16-07-2004
, 11:38 AM
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1. create a particle emitter.
2. create a small nurbs plane (to be instanced) and a large one (to collide with). Deform the big on e a bit so you can see this in action.
4.create some gravity for the particles.
5. make the large plane and the emitter collied together.
6.instance the small plane onto the particles.
7. add the collisionU and collisionV particle attributes. Add two more vector attributes (per particle arrays) one called normal and one called inverseNormal. These are th normals of the point of collision.
8. put this expression on the particleShape
//CODE---------------------------------------
//object to collide with
string $obj = "nurbsPlane2";
//dont really need to do this but it's easier
float $cV = particleShape1.collisionV;
float $cU = particleShape1.collisionU;
//when collision occurs these values change so only do the next bit when they do!
if($cU != -1 || $cV != -1)
{
//build up our pointone surface command. Which will return the xyz of the uv collision point
string $tmp = "pointOnSurface -u "+ particleShape1.collisionU +" -v "+ particleShape1.collisionV +" -position nurbsPlane2";
//eval it
float $collInfo[] = eval($tmp);
//build up another command to do the same for the normal
$tmp = "pointOnSurface -u "+ particleShape1.collisionU +" -v "+ particleShape1.collisionV +" -nn nurbsPlane2";
//eval it
float $iNormal[] = eval($tmp);
//assign the values to the vector attributes created earlier
particleShape1.inverseNormal = <<$iNormal[0] * -1, $iNormal[1] * -1, $iNormal[2] * -1>>;
particleShape1.normal = <<$iNormal[0], $iNormal[1], $iNormal[2]>>;
}
//CODE---------------------------------------
9.set the particle instance options in the particleshape to be
aimdirection: iNormal
aimAxis: normal
10. Hit play... it's should work.
check out the attatched scene file to see it working
post again if it doesnt work.
Alan
oh ye of little faith!!!My guess is no one here will know either, but I figured it was worth a shot.
