Thanks Graham, it's all changed now anyway.  I'm trying to scatter a bunch of 
objects in an area that is centralized around the highlight of a light (null 
attached) and am using a weight map to adjust the particle density in that 
area.  I forgot to take into account the fact that the highlight position needs 
to take into account both the camera and the null instead of just the null.  
Any ideas on how I would need to modify my tree to achieve this?

From: softimage-boun...@listproc.autodesk.com 
[mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Grahame Fuller
Sent: April-27-12 8:34 AM
To: softimage@listproc.autodesk.com
Subject: RE: Evaluating ice weight map gen per frame

I just realized you can get away with a lot fewer calculations if you just 
convert the null's position to the sphere's reference frame. You just need to 
multiply null.kine.global.pos by the inverse of sphere.kine.global, then you 
can get rid of all the other coversions.

gray

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Simon Van de 
Lagemaat
Sent: Thursday, April 26, 2012 07:47 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

I'm sure I'll be calling you again :-)  I'm having some issues with the 
instances on my sphere changing orientation when the sphere rotates.  If I 
can't get it working by tomorrow I'll post an example.

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Grahame Fuller
Sent: April-26-12 4:36 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

Glad to help :)

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Simon Van de 
Lagemaat
Sent: Thursday, April 26, 2012 07:33 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

That did the trick good sir!

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Grahame Fuller
Sent: April-26-12 4:06 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

I suspected there might be normals involved. When converting reference frames 
of "true" vectors as opposed to positions, you need to treat them differently 
(i.e. ignore any translation). There are a few ways to do this e.g.:

- Plug sphere.global.kine.ori and .scl into SRT to Matrix, plug that into a 3x3 
matrix (to force the data type), and use that to multiply the normals before 
the dot product.

- Convert the normals to 4D vectors with W=0, multiply them by 
sphere.global.kine as before, and convert back to 3D vectors before taking the 
dot product.

Note that the above works for "true" vectors in general but normals are even 
more special. If there's any possiblity that there might be non-uniform scaling 
involved, then instead of just using sphere.global.kine you need to plug it 
into a Transpose node and then an Inverse node first. That's not necessary for 
uniform scaling because in that case the inverse of the transpose is the same 
as the original matrix.

And all the above applies only to vectors and normals, not positions.

Good luck!

gray

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Simon Van de 
Lagemaat
Sent: Thursday, April 26, 2012 06:39 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

I kludged this together from wathcing a tutorial on something unrelated to 
weight map gen but it seems to work :-)   I'm in no way experienced with ICE so 
I'm sure I'm messing something up.

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Grahame Fuller
Sent: April-26-12 3:29 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

No, they should work. Can you post a screengrab or scene?

gray

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Simon Van de 
Lagemaat
Sent: Thursday, April 26, 2012 06:21 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

Thanks Graham!  I can now get transform changes on the sphere working but 
orientation changes to the sphere still seem to be borked.  I'm guessing that 
the orientation values aren't included in all of this?

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Grahame Fuller
Sent: April-26-12 2:42 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: RE: Evaluating ice weight map gen per frame

Use Multiply Vector by Matrix to multiply sphere.PointPosition by 
sphere.kine.global first. Then calculate the dot product.

When you get attributes like Sphere.PointPosition by explicit reference (i.e. 
not reading at locations), you get the raw values, which are expressed relative 
to the object centre. Multiplying by the global transform converts to them to 
the global reference frame.

gray

From: 
softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com>
 [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Simon Van de 
Lagemaat
Sent: Thursday, April 26, 2012 05:27 PM
To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com>
Subject: Evaluating ice weight map gen per frame

I'm generating a weight map on a mesh using a simple dot product of a null and 
the surface points on the sphere.  When I animate the sphere the weight map 
generation is ignoring the transforms and acting as if the mesh is in a rest 
state.

How can I get the weight map tree to eval the mesh and its transforms on every 
frame?  I created a simulated ice tree but no luck.

Cheers

Reply via email to