Softimage Blog

Have you ever used Apple’s Shake? Have you ever built macros with Shake? Have you ever wished you could create macros in XSI’s Render Tree?

Well you can, these are called Phenomenon. A Phenomenon is group of shaders exposed to the users as a single entity. You can hide or show, as you see fit, any parameter of the enclosed shaders making a Phenomenon a very powerful tool for sharing shader recipes or building tools for larger productions.

The advantages are:

1. Have a more compact and readable rendertree.
2. Allow for only a set of significant parameters to be tuned by the artist.

Let’s see how it is possible to make up a phenomenon starting from a basic rendertree.

The Goal

The following network returns red if the x coordinate of the point is lower than 1, blue elsewhere. The picture should be quite self-explanatory:

In this case study we want to make a new node enclosing the four primary shaders of the tree, and exposing only three parameters: the two colors and the “threshold” value.

Creating Our SPDL

We need to create a spdl file, which will be later registered.

For those who want a bit of a primer, a SPDL file is a file that defines how XSI will display a certain PPG or Shader. Check the wiki page on SPDL for more info.

The first part of the file contains a header and the declaration of the parameters we want to expose. All the guids must be randomly generated, except the one identifing the output (color) parameter.

SPDL
Version = "2.0.0.0";
Reference = "{19671971-1008-0000-8410-6A45FDB990DD}";
PropertySet "PhenoTest_params"
{
    Parameter "out" output
    {
        title = "PhenoTest";
        guid = "{4C6879FF-7EC8-11D0-8E3B-00A0C90640EC}";
        type = color;
    }
    Parameter "threshold" input
    {
        guid  = "{19671971-1008-0002-8410-6A45FDB990DD}";
        type  = scalar;
        value = 1.0;
        texturable = on;
    }
    Parameter "color1" input
    {
        guid = "{19671971-1010-0001-8410-6A45FDB990DD}";
        type = color;
        value = 1.0 0.0 0.0 1.0;
        texturable = on;
    }
    Parameter "color2" input
    {
        guid = "{19671971-1011-0001-8410-6A45FDB990DD}";
        type = color;
        value = 0.0 0.0 1.0 1.0;
        texturable = on;
    }
}

The bottom part is also quite standard. It just defines the parameter’s defaults and their position in the layout.

BEGIN "{24810490-56FF-11d2-BF23-00A0C982CE5D}"

Defaults
{
    threshold
    {
        Name = "Threshold";
        UIRange = -10.0 to 10.0 by 0.01;
    }
    color1
    {
        Name = "Color 1";
        UIType = "rgba",4;
        Commands = "{F5C75F11-2F05-11d3-AA95-00AA0068D2C0}";
    }
    color2
    {
        Name = "Color 2";
        UIType = "rgba",4;
        Commands = "{F5C75F11-2F05-11d3-AA95-00AA0068D2C0}";
    }
}

Layout "Default"
{
    Name;
    threshold;
    color1;
    color2;
}

Logic
{
}
END

What interests us is the middle section, where you hardcode the connections between shaders. This is, in essence, the part of the SPDL where you create your mini Render Tree.

MetaShader "PhenoTest_declare"
{
    Name = "PhenoTest";
    Type = texture;
    Renderer "mental ray"
    {
        Name = "PhenoTest";

        BeginText

        Node "vector_state"      = guid "{BDE291C7-077A-11D2-8A1A-00A0C9892542}";
        Node "vector_2_scalar"   = guid "{A4F08C3F-AA3A-11D2-AFD4-00A024191B9D}";
        Node "scalar_math_logic" = guid "{4D9E6800-AC2F-11D3-AE56-00A0C96E63E1}";
        Node "boolean_switch"    = guid "{85C16046-BCFA-11D1-90E9-0000F804EB21}";

        Connection "vector_state::mode"	    = value 2;

        Connection "vector_2_scalar::input"     = "vector_state";
        Connection "vector_2_scalar::component" = value 0;

        Connection "scalar_math_logic::input1"  = "vector_2_scalar";
        Connection "scalar_math_logic::input2"  = interface "threshold";
        Connection "scalar_math_logic::op"      = value 2;

        Connection "boolean_switch::input1"     = interface "color1";
        Connection "boolean_switch::input2"     = interface "color2";
        Connection "boolean_switch::switch"     = "scalar_math_logic";

        Connection root                         = "boolean_switch";

        EndText
    }
}

Aching for more details? Read on…

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This entry was posted on Sunday, July 2nd, 2006 at 8:00 am and is filed under Plugins, Programming / Scripting, Rendering, User Interface. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.