[MtoA] Installing the BA shaders in Maya


You can use the BA shaders in Maya with MtoA. The BA shaders are Arnold shaders, so you can use them anywhere that you use Arnold.

Here’s how:

  • Download the Maya mental ray package of the BA shaders. For example, for Maya 2014, the most recent version is
    >>>v25.01.09 Maya 2014 mentalRay
  • Extract the archive. For example, you could extract the archive to a C:\solidangle\BA folder.
  • Set MAYA_SCRIPT_PATH to point to the scripts\AEtemplates folder. For example:
    set MAYA_SCRIPT_PATH=C:\solidangle\BA\140219__baEssential_25.01.09___Maya_2014_MRay\scripts\AETemplates
  • Download the Arnold shaders. For example, for Maya 2014, the most recent version is >>>v25.01.09 Arnold 4.1 (mentalRay addon required for UI)
  • Extract the archive, and set ARNOLD_PLUGIN_PATH to point to the Arnold\win64 folder. For example:
    set ARNOLD_PLUGIN_PATH=C:\solidangle\BA\140219__baEssential_25.01.09___All_Arnold_4_1_3\Arnold\win64
  • Start Maya. The BA shaders should be available, and the AE should look “nice” for the BA shaders.

[MtoA] [SItoA] Distance between shading with Vector State


SItoA includes Arnold versions of the Softimage Vector State and Vector Scalar shaders, which you can use to do build a “distance between” shading network.

Vector State can get you the origin point of a ray and its intersection point, and Vector Scalar can get the distance between those two points.

vector_state_sitoa

You can even use these shaders in Maya (since they are just Arnold shaders). Just put sitoa_shaders somewhere in the ARNOLD_PLUGIN_PATH, and MtoA will load them. The shader UI in the Attribute Editor will be very basic (for example, integer input fields instead of drop-down lists), but you can use the shaders.

vector_state_mtoa

[SItoA] Understanding the Object color mode of the Utility shader


The Utility shader has an Object color mode that assigns colors to objects based on names. Each shape (for example, a polymesh shape or a curves shape or a box shape) gets a unique color, because each shape has a unique name.

If you’re working with SItoA, you may have noticed that the object color changes with each frame:
utility_color_mode

That’s because SItoA gives shapes names like Elephant.Elephant_Mesh.SItoA.4000, which change with every frame.

MtoA doesn’t use the current frame in shape node names, and neither does HtoA (by default). However, HtoA does provide an option for adding a suffix, like the frame number, to the shape node name.

[SItoA] Getting user parameters in the render tree


Arnold nodes can have user-defined parameters, like MyColor in this ASS snippet:

polymesh
{
 name grid3.SItoA.1000
#
# ...
#
 declare MyColor constant RGBA
 MyColor 0.703999996 0 0.526000023 1
}

In Softimage, there are a number of ways you can assign data like MyColor to a polygon mesh. You could use ICE:
userparam_ice_attribute
Or you could use the Arnold User Options property:
userparam_user_options
To access MyColor in the render tree, use the Color Attribute shader:
MyColor_render_tree
If you used ICE, MyColor will appear automatically in the Attribute list. But if you used the User Options property, you’ll have to use a script one-liner to set the Attribute value. That’s because Softimage doesn’t know about the user parameters on Arnold nodes: those come into existence only when SItoA translates the scene to Arnold.

Application.SetValue("Sources.Materials.DefaultLib.Material.Color_Attribute.attribute", "MyColor", "")

On a related note, the MtoA shader userDataColor does the same thing as the SItoA Color Attribute shader: it uses AiUDataGetRGBA() to get a color from a user parameter on the object being shaded. With SItoA 3.0, the Arnold > DLL Shaders menu makes it pretty easy to use an MtoA shader in Softimage.
mtoa_userDataColor

[MtoA] Installing custom shaders


So, you’ve downloaded some custom shaders and you want to get them into Maya? Here’s how:

  • Set ARNOLD_PLUGIN_PATH to point to the location of the shader DLL/SO and MTD files.
  • Set MTOA_TEMPLATES_PATH to point to the location of the shader template .PY files.

That’s it. MtoA uses those environment variables to find the shaders (the .DLL or .SO files), the shader metadata files (.MTD), and the shader templates (.PY).

A metadata file tells Maya how to handle the shader (for example, where to show it in the Assign New Materials window).
A shader template defines the UI for the shader in the Attribute Editor.

Object color mode


The Arnold Utility shader has an Object color mode, which assigns colors based on shape names. When we say “shapes”, we don’t mean Maya shape nodes; we mean the Arnold shapes.

C:\solidangle\mtoadeploy\2014\bin>kick -nodes | find "shape"
 box                              shape
 cone                             shape
 curves                           shape
 cylinder                         shape
 disk                             shape
 ginstance                        shape
 implicit                         shape
 nurbs                            shape
 plane                            shape
 points                           shape
 polymesh                         shape
 procedural                       shape
 sphere                           shape

All these nodes have a name parameter (for example, polymesh.name) that is a unique string identifier in the Arnold universe. So when you use the Object color mode, you get a unique color for each node.

If you’re using Softimage, note that SItoA puts the frame number into polymesh.name, so you’ll get a different color on each frame if you use the Object color mode. For example, on frame 5 a polymesh might be named “Dog_Mesh.SItoA.5000”, and on frame 6, “Dog_Mesh.SItoA.6000”.

In this render region comparison, you have frame 5 on the left, and frame 6 on the right:
dog_color_mode

In a case like this, you would use the Object ID color mode instead. SItoA automatically assigns unique IDs to the shape nodes (MtoA doesn’t).

Rayswitching shadow rays


The ray_switch node lets you evaluate different shading trees for different ray types. In general, it’s used to provide a simpler shading tree for secondary rays, such as diffuse, glossy, or shadow rays. So when a camera ray hits the object, you can do one thing, but when a secondary ray hits the object, you can do another, simpler thing 🙂

For shadow rays, it’s not the color that matters, but whether the object blocks the shadow ray from a light. For example, if an object is opaque, then it doesn’t matter whether ray_switch returns red or blue or green or yellow for the shadow rays: the object is still opaque and blocking the light. So, you could use a ray_switch.shadow to plug in a simple standard shader that provides just the opacity mask.

ray_switch_shadow_opacity

Just for kicks: Printing out shading trees


kick -tree prints the shading network for a shader node. For example, given this:

polymesh
{
 ...
 shader "Sources.Materials.DefaultLib.Material.standard.SItoA.41000.1" 
 ...
}

standard
{
 name Sources.Materials.DefaultLib.Material.standard.SItoA.41000.1
 
}

You can print out the shader tree for the standard shader like this:

set ASS_FILE=//Projects/Support/Arnold_Scenes/example.ass
set NODE=Sources.Materials.DefaultLib.Material.standard.SItoA.41000.1
set SHADER_PATH=%SITOA_BIN%
%KICK_PATH%\kick.exe -tree %NODE%  -i %ASS_FILE% -l %SHADER_PATH%

For a [simple] shading tree that looks like this:
SimpleTree
You would get this:

standard:Sources.Materials.DefaultLib.Material.standard.SItoA.41000.1
  |
  +-Kd_color = txt2d_image_explicit:Sources.Materials.DefaultLib.Material.Image.SItoA.41000.2
  |   |
  |   +-tex = sib_image_clip:Sources.Materials.DefaultLib.Material.noIcon_pic.SItoA.41000.3
  |
  +-opacity = txt2d_image_explicit:Sources.Materials.DefaultLib.Material.Image.SItoA.41000.2
      |
      +-tex = sib_image_clip:Sources.Materials.DefaultLib.Material.noIcon_pic.SItoA.41000.3

max depth:       2
total shaders:   5
cycles detected: 0

shader counts:
  2 txt2d_image_explicit
  2 sib_image_clip
  1 standard

one-to-many connections:
  2 txt2d_image_explicit:Sources.Materials.DefaultLib.Material.Image.SItoA.41000.2
  2 sib_image_clip:Sources.Materials.DefaultLib.Material.noIcon_pic.SItoA.41000.3

Notice that txt2d_image_explicit and sib_image_clip are counted twice, because those branches are plugged into two different ports on the standard shader.

SITOA: Adding Arnold materials through scripting


If you want to apply Arnold materials through scripting, there are a couple of undocumented commands you can use:

  • SITOA_AddMaterial takes the shader family (for example, Material or Texture) and the name of a shader, and connects that shader to the surface port on the Material node.
    # Add a standard material to the selected object
    SITOA_AddMaterial( "Material", "standard" )
    
    # Add ambient_occlusion to the selected object
    SITOA_AddMaterial( "Texture", "ambient_occlusion" )
    
  • SITOA_AddShader is similar, but it also takes a connection point as an argument, so you can connect to a specific port, such as the Environment or Displacement port.
    # Add a vector displacement shader
    SITOA_AddShader("Texture", "sta_vector_displacement", "displacement" )
    

However, neither of these commands return anything. So if you wanted to name the material, it’s not so easy. SITOA_AddMaterial does apply to the selection, so you could go through the selection to get the new material:

# Python
Application.SITOA_AddMaterial("Material", "standard")
sel = Application.Selection
mat = sel(0).Material
mat.Name = "MyStandardMaterial77"

You could write your own function with X3DObject.AddMaterial.

Here’s the simplest possible version. I don’t specify the path to a preset, just the name of the shader. That’s not terribly efficient, because Softimage now has to search for the preset (and that took about 0.2 seconds on my machine).

si = Application

def add_material( o, shader_name ):
	return o.AddMaterial( shader_name )

mat = add_material( si.Selection(0), 'Material', 'Standard' )
mat.Name = 'My_Standard_Mat'

Here’s a version that builds the path to the preset (just like the SITOA commands do), but that doesn’t require the shader family, just the name of the shader.

# dictionary of shader families, keyed by shader name
shader_types = {
  'ray_switch' : 'Material' , 
  'sta_vector_displacement' : 'Texture' , 
  'wireframe' : 'Material' , 
  'sta_displacement' : 'Texture' , 
  'ambient_occlusion' : 'Texture' , 
  'skin_sss' : 'Material' , 
  'sta_camera_projection' : 'Texture' , 
  'utility' : 'Texture' , 
  'bump3d' : 'Texture' , 
  'standard' : 'Material' , 
  'complex_fresnel' : 'Texture' , 
  'bump2d' : 'Texture' , 
  'motion_vector' : 'Material' , 
  'hair' : 'Material' , 
  'noise' : 'Texture' , 
  }


si = Application

def add_material( o, shader_name ):
	arnoldPlugin = si.plugins("Arnold Shaders");
	dspresets = XSIUtils.BuildPath( arnoldPlugin.OriginPath, '..', '..', 'Data', 'DSPresets' )
	mat = None
	if shader_name in shader_types:
		preset = XSIUtils.BuildPath( dspresets, 'Shaders', shader_types[shader_name], '%s.Preset' % shader_name )
		mat = o.AddMaterial( preset )
	return mat


mat = add_material( si.Selection(0), 'noise' )

mat.Name = 'My_Noise'

Noise, world coordinates, and offsets


If you’re using world coordinates for your noise, then obviously as an object moves in global space, the noise will change. Here I’ve extracted a polygon and moved it: same shader tree that uses noise, but different noise because I’m using world coordinates.
noise_world

You could keep the same noise by applying an offset equal to the translation:
noise_world_offset_1
Note that I’ve assumed that there’s no scaling of the noise. If there was, I’d have to multiply my offset by the same scaling.