Calculate "from" "to" using Matrix?

[Atom]

Hi All,

 

I am trying to calculate the "from" "to" parameters for a Renderman light shader using the Houdini matrix information.

 

The "from" is easy, it is simply the location extracted from the matrix.

n = hou.node(light_name)
if n != None:
    mtx = n.worldTransform()
    # from
    pos=mtx.extractTranslates() 

It is the "to" value that I am having trouble with. I realize I need to use the rotation information projected along a vector to produce a new location but I am not quite sure how to do that using Houdini Python.

 

Here is an example I found in some Blender python code accomplishing the same task. How would I translate that to Houdini based Python?

    m = ob.matrix_world
    loc = m.to_translation()
    lvec = loc - (m.to_quaternion() * mathutils.Vector((0,0,1)))

Edited April 27, 2015 by Atom

[Atom]

I tried rotating it right but it did not work.

 

Does anyone know how to  calculate the "from" "to" parameters for a Renderman light shader using the Houdini matrix information?

[Atom]

Can someone help with this it has been over a week and I still need to accomplish this goal.

 

Where is the begging emoticon...?      

[symek]

n = hou.node(light_name)
if n != None:
    mtx = n.worldTransform()
    # from
    pos=mtx.extractTranslates()
    # to
    direction = hou.Vector3((0, 0, -1)) * mtx
    # and depending on your needs evantually:
    lookat  = pos + direction

I'm not sure if vector should be pointed backwards though but this is easy fix anyway.

[Atom]

Thank you Symek, I am finally getting back to this task.

 

Your code example helps a lot!