Class

Shape

Synopsis

Creates instances of shapes and lights as defined by the nodes and node_idxs parameters. Per instance transformation, visibility and shader overrides can be specified via the builtin instance_matrix, instance_visibility and instance_shader parameters. Any other per instance shape or light overrides or user parameters can be specified via constant array type user parameters, started with the instance_ prefix. For example overriding intensity of light instances:

declare instance_intensity constant ARRAY FLOAT
instance_intensity 10 1 FLOAT
 1.4 1 1 1 1 2.2 2 1 1 1

In case all instances share the same parameter value, a single value can be set. For example:

declare instance_intensity constant ARRAY FLOAT
instance_intensity 1

Currently instance generation is quite expensive, generating huge amount of instances (e.g. 10 millions) can result in high node init and node update time and memory usage.

Array parameters

Specifying per instance array type parameters requires some special care. Arrays can be defined as constant, uniform, varying, etc, called the category of the array. By default the same category is set as defined on the referenced shapes or lights. In case the array does not exist, the category can be explicitly set via a string type user parameter, started with the arraycategory_ prefix.

This example defines the integer array called myparam on each 3 instances and sets the category to uniform:

 declare instance_myparam constant ARRAY ARRAY
 instance_myparam 3 1 ARRAY 
 10 1 INT
 2 3 2 3 2 3 2 3 2 3
 10 1 INT
 2 1 2 1 2 3 2 3 2 3
 10 1 INT
 1 1 1 2 2 2 3 3 3 3
 declare arraycategory_myparam constant STRING
 arraycategory_myparam "uniform"  

Override specific instances

In certain cases only some of the instances have overrides and specifying a value for each instance would be inefficient. A user data array with the instanceidxs_ prefix can be declared in this case, which tells the list of instances with overrides.

This example defines overrides of parameter myparam for instance 0 and 3, keeping the default value on all other instances.

 declare instance_myparam constant ARRAY ARRAY
 instance_myparam 2 1 ARRAY 
 10 1 INT
 2 3 2 3 2 3 2 3 2 3
 10 1 INT
 2 1 2 1 2 3 2 3 2 3
 declare instanceidxs_myparam constant ARRAY UINT
 instanceidxs_myparam 2 1 UINT
 0 3

If the same override is defined on multiple instances, they can be defined only once and a user data array with the valueidxs_ prefix can be used to describe the relationship between overrides and instances. 

This example defines an override of parameter myparam for instance 0 and 3, and a different override for instance 1 and 4.

 declare instance_myparam constant ARRAY ARRAY
 instance_myparam 2 1 ARRAY 
 10 1 INT
 2 3 2 3 2 3 2 3 2 3
 10 1 INT
 2 1 2 1 2 3 2 3 2 3
 declare instanceidxs_myparam constant ARRAY UINT
 instanceidxs_myparam 4 1 UINT
 0 3 1 4
 declare valueidxs_myparam constant ARRAY UINT
 valueidxs_myparam 4 1 UINT
 0 0 1 1



visibility

You can selectively disable an object's visibility for the various types of rays in the renderer. By default, objects are visible to all types of rays. Camera - Camera (AA) rays (i.e., primary or view rays). Shadow - shadow rays fired in the direct lighting calculations. Specular - specular_reflection rays. Transmission - transmission rays. Diffuse - indirect_diffuse rays (i.e. global illumination or GI rays). Specular - indirect_specular rays (i.e. specular reflection rays).

To set the visibility, add up the values of the rays you want to "see" the object.

For example, if an object is visible to the camera (primary visibility), and to transmission (both diffuse and specular), then that’s visibility 13 (1 + 4 + 8).


Ray typeDecimal Value
Camera (Primary Visibility)1
Shadow (Casts Shadows)2
Diffuse transmission4
Specular transmission8
Volume16
Diffuse reflection32
Specular reflection64
SSS (subsurface)128

sidedness

Just like you can disable the visibility for specific ray types, you can also change an object's sidedness depending on the ray type. By default, objects are double-sided for all rays. By unclicking any of these checkboxes, the object will become single-sided, which means that those parts of the object whose normal vector points away from the incoming ray direction will not be rendered.

receive_shadows

Determines whether or not the object picks up shadows from other objects.

self_shadows

Determines whether or not the object casts shadows on itself.


invert_normals

Invert normals (so that normals face inwards and not outwards).

ray_bias

Raytrace bias value specified for the object.

matrix

Transformation matrix. This can be either a single matrix or an array of matrices that define the SRT motion of the object for the current frame (the matrices define the motion for the full-frame, not just between the shutter open - close time).

transform_type

Specifies what type of motion the object has. Options are linearrotate_about_center, and rotate_about_originlinear corresponds to the linear interpolation between matrices. rotate_about_origin corresponds to curved_motionblur=true. Unlike, rotate_about_origin which sets the rotation pivot at the origin, rotate_about_center will rotate about the object's center. This is the default mode and is useful for wheels, propellers, and other objects which spin.

shader

An array of nodes pointing to the shader or shaders in the case of per-face shader assignment.

opaque

As of Arnold 5.3, this flag is set automatically by changing the opacity or transmission on a material.

Determines whether the object is considered opaque (transparent). By default, Arnold built-in shaders set the opaque flag automatically, based on whether or not the shader settings would require disabling the opaque flag on the object to render correctly. For example, it's no longer necessary to manually disable the opaque flag to get transparent shadows for a glass shader.


Exceptions are curves and points when min_pixel_width is in use, and OSL shaders.  



matte

The matte option enables you to create holdout effects by rendering the alpha as zero.

use_light_group

A boolean to enable selective light linking

light_group

An array of nodes pointing to the lights that will affect the node if use_light_group is enabled.

use_shadow_group

A boolean to enable selective shadow linking.

shadow_group

An array of nodes pointing to the lights that will not cast shadows on the polymesh, if use_shadow_group is enabled.

trace_sets

An array of strings each of which names a trace set. A custom shader must be used to make effective use of these strings via the AiShaderGlobalsSetTraceSet and the AiShaderGlobalsUnsetTraceSet API calls.

It is possible to tag objects to be part of one or many trace sets. The trace_set shader tags specific rays with an inclusive or exclusive trace set. Both geometry and rays can be tagged with trace sets:

  • A piece of geometry can have none or any number of trace set tags.
  • A ray can optionally have one trace set tag, and it can be exclusive or inclusive.


The way those two tags interact makes it possible to control visibility for specific rays:

  • A ray with no trace set will hit all geometry.
  • A ray tagged with an inclusive trace set will only hit geometry which has that trace set tag.
  • A ray tagged with an exclusive trace set will only see geometry that does NOT have that trace set tag.

motion_start

The time at which the first motion key of the shape is sampled. Other motion keys must be uniformly spaced within this range. Times can be absolute or relative as long as shutter and motion times use the same convention. By convention, the times are frame relative. For example, start and end times -0.5 to 0.5 indicate that two motion keys will be sampled midway between the previous and current frame, and the current frame and next frame. This is applied to cameras, lights, and shapes.

motion_end

The time at which the last motion key of the shape is sampled. Other motion keys must be uniformly spaced within this range. Times can be absolute or relative as long as shutter and motion times use the same convention. By convention, the times are frame relative. For example, start and end times -0.5 to 0.5 indicate that two motion keys will be sampled midway between the previous and current frame, and the current frame and next frame. This is applied to cameras, lights, and shapes.

id

Unique ID for a node in the Arnold scene. 

override_nodes

Nodes inside the procedural can be replaced by other nodes with this parameter. This may be used for example to replace shaders in an existing .ass procedural. When the parameter is enabled, nodes in the immediate parent scope of the procedural will replace identically named nodes inside the procedural.

namespace

Procedurals can declare a custom namespace using this parameter. This custom namespace can be used instead of the procedural name, to reference contents through absolute or relative paths. Multiple procedurals can share the same namespace by using the same custom name. Also, they can declare an empty name and they will use the global namespace.

operator

The operator graph is evaluated specifically for this procedural from the operator node defined here, denoted as the target operator.

nodes

Array of shapes and lights from the scene which will be instanced.

node_idxs

This array describes which shape or light is referenced by each instance by defining the index in the nodes array. If all instances reference the same shape, a single value can be specified instead of an array.

instance_matrix

Transformation matrix per instance.

instance_visibility

Shape visibility override per instance.

instance_shader

Shader override per instance.



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