Appendix C: Custom vertex data

Previously, UVs, ColorPerVertex, and User Data per Vertex are being referenced by index. This creates a pipeline challenge since it is difficult to enforce indices.

Now, by default, a data block is added to each shape node that provides the name of each piece of data (UVs, CVP, and custom data per vertex). You can query this table from within the shader API in order to retrieve and resolve the string value passed to a shader.

You can assign shading networks to many objects and assign the ColorPerVertex and UVs at render time without explicitly creating a connection within the Maya scene. At render time, the shader would be responsible for converting Name references into per-instance or per-shapeNode indices.

An example of this data block is shown below:

data "pPlaneShape1:PerVertexNomenclature"
 "PerVertexNomenclature"
 (
 "magicnumber" 5149248936,
 "tex" // texture space or Maya UVs
 [
 { "name" "uvset1", "index" 0 }
 { "name" "myUVset", "index" 1 }
 { "name" "bakeUV", "index" 2 }
 ],
 "cpv" // color per vertex (RGB only)
 [
 { "name" "ColorSet1", "index" 3 }
 { "name" "CPV_DirtMask", "index" 4 }
 { "name" "CPV_WetMask", "index" 5 }
 ],
 "cudpv" //custom data per vertex
 [
 { "name" "LightIndexField", "index" 6 }
 ]
 )
object "pPlaneShape1"
 visible on
 shadow 3
 transparency 3
 reflection 3
 refraction 3
 finalgather 3
 face both
 tagged
 trilist vertex 4 p n t 2 b 2 u 3 triangle 2
 [
 vertex data goes here
 ]
 [
 0 0 1 3
 0 3 1 2
 ]
 end trilist
 data "pPlaneShape1:PerVertexNomenclature"
end object
shader "DirtMapCPVLookup1" "myCustomVertexColor" ( "cpvname" "CPV_Dirtmask", .... )

To turn this off, you can select between the following methods:

• Turn off Export Custom Data under the Customization section of the Translation section under the Render Settings: mental ray tabs, Options tab. This disables the recognition of custom vertex data and the whole data info block translation; but it does not disable translation of Maya's standard vertex data (UV and color sets). This is the primary control to disable 'info' data block translation.
• Turn off Export Vertex Colors under the Translation section of the Options tab of the Render Settings: mental ray tabs. This disables vertex color translation. As a consequence, the 'cpv' section of the 'info' data block is not translated. If this option is enabled, then vertex color sets are translated (along with the 'info') regardless of usage of the node mentalrayVertexColors in a shading graph.