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Thread: Function Nodes not effecting bump

  1. #1

    Function Nodes not effecting bump

    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

  2. #2
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    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.

  3. #3
    Ahh, no, ok, I didn't know that. Ok thanks Denis, I'll give that a try!

  4. #4
    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...

  5. #5
    Goes bump in the night RebelHill's Avatar
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    try using wither the Tools>Limiter, or the Math>Scalar>Clamp nodes, either of those should likely do the trick.

  6. #6
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    Quote Originally Posted by Mattoo View Post
    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:

    Click image for larger version. 

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    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:

    Click image for larger version. 

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

    Denis.

  7. #7
    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

  8. #8
    Copy the node and use the color output of node 1 to bump-amplitude the original one.

  9. #9
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    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.

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