What Is An Args File?

Args files are XML files that provide the user interface for shader parameters. RenderMan for Katana looks for Args files in one of the following directories:

1. Args subdirectory of the shader directory. This is recommended.
2. ../Args directory relative to the shader directory.
3. Args subdirectory of $KATANA_RESOURCES.

Args files are required for plugin (C++) shaders; they are the only source for information to the DCC about the shader parameter types, defaults, etc. (Note, however, that RenderMan itself does not read the Args file; it gets this information from the parameter table of the shading plugin). The name of the Args file must have the same base name as the shader, e.g. PxrBump.args for PxrBump.so, PxrRectLight.args for PxrRectLight.so, etc. The order of the shader parameters in the Args file represents the order in which they will appear in the user interface.

How To Create An Args File

An Args file is an ASCII file that can be created manually using any text editor.

Note:  If you are using RenderMan for Katana some aspects the user interface can be edited interactively then exported to the Args file. Refer to the documentation in your Katana installation for more details ($KATANA_HOME/docs/pdf/ArgsFiles.pdf).

Args File Format

The basic format for an args file is as follows:

<args format="1.0">
    <param name="someParameter"/>
    <param name="anotherParameter">
</args>

Shader Type

PRMan extension

The type of shader is specified using the shaderType element. This is necessary for plugin shaders as there is no mechanism by which to query the shader type. An example for a pattern plugin would be:

<shaderType>
    <tag value="pattern"/>
</shaderType>

Basic Elements

param

Elements of type param describe the presence and order of parameters within the shader UI. Each param element is required to have a name property; all other properties are optional. See below for a detailed list of param properties.

page

Parameters may be grouped into pages via page properties, either as a stand-alone page or nested via dot-delimited values:

<param name="someParameter" page="Lighting" />
<param name="anotherParameter" page="Lighting.Advanced"/>

Page grouping may also be specified via enclosing page elements:

<page name="Lighting">
    <param name="someParameter"/>
    <page name="Advanced">
        <param name="anotherParameter"/>
    </page>
</page>

Parameters within a page group are collected in the UI under a group widget pane that can be "open" or "closed". By default the group is closed but this behavior can be modified using the open property on the page element:

<page name="Advanced" open="True">
    <param name="anotherParameter"/>
</page>

help

Embedded documentation may be specified with either a property or a child element of type help:

<param name="someParameter" help="This parameter increases render time."/>

When using a child help element, its contents are interpreted as XHTML for more sophisticated formatting:

<param name="anotherParameter">
    <help>
        <p>
        This parameter is <b>very</b> important.
        </p>
        <i>Please be careful when setting it.</i>
    </help>
</param>

Both forms are also supported on args and page elements. For more details on embedded documentation and other features of the help element please see the  Args File UI Hinting  document.

Comments

Comments are the same as they are in HTML and XML:

<!-- Useful commentary goes here. -->

Elements and Properties

Args files were originally created as a way of providing UI hinting for shaders in Katana. PRMan has since adopted and extended this format. Katana's set of elements, parameters and tags are described in detail in the Katana documentation and in the Args File UI Hinting document. Below is a summary of the most commonly used components for the built-in PRMan shaders. Portions that have been adopted specifically for PRMan and RenderMan for Katana and Maya are noted.

<param name="resolution" type="float"
       arraySize="2" default="1024 1024"/>

<param name="layers" isDynamicArray="1"
       arraySize="-1" widget="dynamicArray"/>

<param name="diffuseColor" widget="default"/>

<param name="channel" type="string" widget="popup" options="R|G|B|A"/>

<param name="stops" label="Stops" type="float"
       default="0.0" min="-10" max="10"
       slider="True" slidermin="-4" slidermax="4"
       widget="float">

<param name="atlasStyle" type="int" default="0" widget="mapper">
    <hintdict name="options">
        <string name="None"   value="0"/>
        <string name="MARI"   value="1"/>
        <string name="Mudbox" value="2"/>
    </hintdict>
</param>

<param name="filename"
       label="Filename"
       type="string"
       default=""
       widget="assetIdInput"
       options="texture"
       connectable="False">
</param>

<page name="Color Ramp" open="False">
        <param name="colorRamp"
               label="Color Ramp"
               type="int" widget="colorRamp" default="4"
               colorBarHeight="25" restrictComponents="True">
        </param>
        <param name="colorRamp_Knots"
               type="float"
               widget="null"
               default="0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1" arraySize="16"/>
        <param name="colorRamp_Colors"
               type="color"
               widget="null"
               default="1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1" 
               arraySize="16"/>
        <param name="colorRamp_Interpolation"
               type="string"
               default="linear"
               widget="null" options="linear|catmull-rom|bspline|constant"/>
 </page>

<page name="Falloff" open="False">
        <param name="falloff"
               label="Fall Off"
               type="int" widget="floatRamp" default="6"
               connectable="False"
               bgColor="0.25 0.25 0.25" underSplineColor="0.5 0.5 0.5">
            <help>falloff: Controls the transition from the core to the edge.</help>
        </param>
        <param name="falloff_Knots"
               type="float"
               widget="null"
               default="0 0 0.3 0.7 1 1 1 1 1 1 1 1 1 1 1 1" 
               arraySize="16"/>
        <param name="falloff_Floats"
               type="float"
               widget="null"
               default="0 0 0.2 0.8 1 1 1 1 1 1 1 1 1 1 1 1" 
               arraySize="16"/>
        <param name="falloff_Interpolation"
               type="string"
               default="bspline"
               widget="null" options="linear|catmull-rom|bspline|constant"/>
</page>

Input and Output Tags

Katana requirement: All input and output tag values must be all lowercase.

Each shader can define a set of outputs in the args file. In addition each parameter of a shader can define what types of input are allowed.

Output connections are specified using the output element with a series of tags enumerating the output types:

<output name="resultRGB">
    <tags>
        <tag value="color"/>
        <tag value="diffuse"/>
    </tags>
</output>

Input connections are defined as a tags child element of param:

<param name="inputDiffuse" type="color" widget="default">
    <tags>
        <tag value = "diffuse"/>
    </tags>
</param>

Tag values can be any valid output connection string. Boolean logic is also available for more advanced rules about input connection validity:

<param name="inputDiffuse" type="color" widget="color">
    <tags>
        <tag value = "(diffuse and color) or struct"/>
    </tags>
</param>

Connections are disabled by setting connectable="False"

<param name="invertT"
       type="int"
       widget="checkBox"
       connectable="False">
</param>

Please see the Katana Technical Guide section on Typed Connection Checking for more details about input/output tags and input connection boolean logic.

Parsing Args Files

PRMan uses RapidXML for parsing Args files. See $RMANTREE/lib/examples/args/parse/parseArgs.cpp for an example of a standalone C++ program to parse an .args file. To build this program on Linux, for example, run:

make -f Makefile.linux
parseArgs $RMANTREE/lib/plugins/Args/PxrChecker.args

parseArgs will output a list of parameters and their attributes that are supported in RenderMan for Katana and Maya.

Sample Args File

The PxrChecker.args file (for PxrChecker.so shader) is provided as an example, to provide more information about the structure of the file:

<args format="1.0">
    <shaderType>
        <tag value="pattern"/>
    </shaderType>
    <help>A checker pattern</help>
    <param name="colorA"
        label="Color A"
        type="color"
        default="1.0 1.0 1.0"
        widget="color">
    </param>
    <param name="colorB"
        label="Color B"
        type="color"
        default="0.0 0.0 0.0"
        widget="color">
    </param>
    <param name="manifold"
        label="Manifold"
        type="struct"
        default=""
        widget="default">
        <tags>
            <tag value="struct"/>
            <tag value="manifold"/>
        </tags>
    </param>
    <output name="resultRGB"> 
        <tags>
            <tag value ="color"/>
            <tag value ="vector"/>
            <tag value ="normal"/>
            <tag value ="point"/>
        </tags>
    </output>
    <output name="resultR">
        <tags>
            <tag value ="float"/>
        </tags>
    </output>
    <output name="resultG">
        <tags>
            <tag value ="float"/>
        </tags>
    </output>
    <output name="resultB">
        <tags>
            <tag value ="float"/>
        </tags>
    </output>
    <rfmdata nodeid="1053270" classification="rendernode/RenderMan/pattern"/>
</args>