PDA

View Full Version : Function Nodes not effecting bump



Mattoo
06-12-2008, 05:03 AM
I have a simple Crumple procedural as a bump and I want to plug a function node (tried a bias and Boxstep) into it. It works fine if I output straight into the colour, but the Function node has no effect on the Bump of the crumple!

I'm using LW 9.3.1


Strangely the IFW2 nodes work fine doing this, it's just the Lightwave nodes that are apparently broken.

If anyone has any suggestions I'd be very pleased to hear them.


tnx
Matt

dpont
06-12-2008, 06:43 AM
Actually the Function input do a modification only
the opacity channel and so color output is modified too,
but as you know Bump output is only relied to
the Bump Amplitude channel not the opacity and
will not be affected by the input function.
There's a workaround a bit slower, use a color
or alpha output and convert it to a bump output
with the DP_Kit' ScalarToBump node, to get benefit
of the function input.

Denis.

Mattoo
06-12-2008, 07:31 AM
Ahh, no, ok, I didn't know that. Ok thanks Denis, I'll give that a try!

Mattoo
06-12-2008, 09:11 AM
I tried Scalar2Bump from the alpha (on crumple) and it produces a very different effect from the standard bump output.

What I'm trying to do is clamp the upper range of an inverted crumple to make dry cracked ground. Previously I would have used a gradient set to 'Previous Layer' to control a bump in this way. The Function nodes seemed to do similar things, but as I've learned they only work on the RGB... :grumpy:

RebelHill
06-12-2008, 04:18 PM
try using wither the Tools>Limiter, or the Math>Scalar>Clamp nodes, either of those should likely do the trick.

dpont
06-13-2008, 02:24 AM
I tried Scalar2Bump from the alpha (on crumple) and it produces a very different effect from the standard bump output...

I think that the bump formulae is not always exactly the same
than the one used for alpha and color in a procedural texture.

Here the original Crackel node output Bump with default values:

59729

Here the Color of Crackel node input in a Scalar2Bump node,
Small Scale decrease to half value, Bump Amplitude
set to 200% in Scalar2Bump node:

59728

...But less easy for matching results in Crumple node.

Denis.

Mattoo
06-14-2008, 04:09 PM
Thanks Denis. My attempts to replicate via scalar2bump were with Crumple, so that explains why I dismissed this avenue.

RebelHill: Thanks, that's what I did in the end!


cheers
Matt

Thomas M.
06-15-2008, 02:51 AM
Copy the node and use the color output of node 1 to bump-amplitude the original one.

dpont
06-15-2008, 06:48 AM
Depends of which function you are using, but this
is an approximate solution to get the function in the bump
output.

A bump amplitude is strictly a scale/multiply factor applied
to the resulted bump vector, instead the function should be
applied to the samples before building the bump vector
but the most important thing is that a function is not necessary
a scale factor but could be an inversion (0 become 1)
or even a replacement value, currently it could output
anything based on the value intercepted in the procedural,
(also this value could be intercepted anywhere in the
procedural evaluation, most current case is the scalar
result of the algorithm),
this is something you could not fake through a simple
scaling modification.

In the case of an inversion function for alpha you get:
alpha 0-> function 1 ->alpha 1 = 1
if you input the color or alpha of the first node to the bump amp:
alpha 0-> function 1 ->bump amp 1 x alpha 0 = 0

That's why also the function is not assimilated to a scalar
input with its yellow color.

Denis.