It was only in a small-ish room but the hustle and bustle outside the Solid Angle Arnold workshop showed just how much buzz this renderer has. In the session, Solid Angle founder Marcos Fajardo detailed the growth of his company (now more than 20 people) and promised a new website (traditionally a rendering formula) and that they would be ‘more open’.
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In this video, I show how to a color mask AOV using a custom AOV and the Utility shader. Topics covered include:
– Creating a custom AOV
– Setting the default shader for a custom AOV
– Setting up the Utility shader to output a color for each shape
– Understanding the difference between the Color and Color ID color modes
If you want to change something in existing ASS files, don’t write an ad-hoc script or your own parser for the ASS file. Use the Arnold API. The Arnold API includes a set of Python bindings, so you can fairly quickly whip up a script to do whatever it is you need to do 🙂
For example, we recently discovered (and fixed) an issue where exported ASS files were missing procedural nodes. SItoA exports hair data in chunks (one chunk for every 200K hairs), but the exported ASS had just one procedural for the first chunk (chunk 0), but there should be one procedural for each chunk.
Here’s what the procedural for chunk 0 on frame 5 looks like. The missing procedurals would be for bin files like Hair.chunk.1.5.bin, Hair.chunk.2.5.bin, and so on.
procedural
{
name Hair.SItoA.5000
dso "sitoa_curves_proc.dll"
data "//Projects/Support/Arnold_Scenes/Hair.chunk.0.5.bin"
load_at_init on
}
So, for my first dive into the Arnold API, I put together a basic little script to add the missing procedurals. To do this, I had to learn how to:
from arnold import *
import glob
ass_file = "Hair_Archive.ass"
AiBegin()
AiMsgSetConsoleFlags(AI_LOG_ALL)
AiASSLoad(ass_file, AI_NODE_ALL)
# Iterate over all shape nodes, which includes procedural nodes
iter = AiUniverseGetNodeIterator(AI_NODE_SHAPE);
while not AiNodeIteratorFinished(iter):
node = AiNodeIteratorGetNext(iter)
#print AiNodeGetName( node )
# Is the node a procedural?
if AiNodeIs( node, "procedural" ):
data = AiNodeGetStr( node, "data" )
name = AiNodeGetStr( node, "name" )
# Find all other chunk.<chunk-number>.<frame>.bin files
chunks = glob.glob( data.replace( 'chunk.0', 'chunk.*' ) )
# Add procedural nodes for chunks 1,2,3...
for i in range(1,len(chunks)):
n = AiNode("procedural");
AiNodeSetStr(n, "name", "%s.%s" % (name, i) )
AiNodeSetStr(n, "dso", "sitoa_curves_proc.dll")
AiNodeSetStr(n, "data", data.replace( 'chunk.0', 'chunk.%s' % i ) )
AiNodeSetBool(n, "load_at_init", True)
AiNodeIteratorDestroy(iter)
AiASSWrite(ass_file, AI_NODE_ALL, False)
AiEnd()
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:
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.
If you need to change the same Arnold attributes on many nodes, use the Attribute Spreadsheet. For example, suppose you wanted to turn off the Opaque attribute on a number of objects in your scene. Here’s how to do it:
If you’re doing technical support like me, you gotta love things like kick -licensecheck. I wish we’d had something like this at Softimage. This license check will tell you:
In this example, I’m running Maya and the license server on the same computer. That’s why none of the environment variables are set, but the licensecheck still shows that there’s a license available. By default, Arnold will connect to 5053@localhost to get a license.
AOV Composition allows opacity and transparency to carry forward into AOVs. It works only for RGB AOVs, so you won’t see it in the render region (because the xsi display driver always outputs RGBA AOVs).
For example, suppose you have a textured grid with an opacity map:
In the render region, the Main AOV is fine, but the Arnold Direct Diffuse doesn’t have the opacity, even if you enable AOV Composition:
However, if you render out the image (with AOV Composition enabled and the Direct Diffuse format set to RGB), you’ll get what you expected:
The Noise shader can use different coordinate systems when it evaluates the noise.
The name “Pref” is easier to understand if you think of it like a variable name. So, when it comes to noise, P is a point in world space, Po is in object space, and Pref is in “reference space” aka the “bind pose”.
For the Noise shader, the advantage of using Pref is that it prevents the noise from swimming over the surface of the object as the object deforms (as long as the deforms are above the Modeling stack). As the object deforms, Po is a point on that deformed geometry, so Po is constantly changing. In contrast, Pref is a point on the geometry that came out of the Modeling stack. So the noise sticks to the “bind pose”.
Note the difference between Pref and the two other coordinate systems (World and Object).
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.
You could keep the same noise by applying an offset equal to the translation:
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.
Arnold Support Corner 