Houdini 中文帮助文档

Point Instance Procedural

此节点会获取一系列的物体，并在渲染时将它们分布为给定的数量。每个点可以指定一个材质到其替换的物体上（独立于物体自身）。主要的好处是在渲染时，不像Copy SOP那样，只有内存会从非常小的源物体中超出。因为替换单个物体1000次不会使用太多内存。

Parameters

Main

Point Object The object that contains the points to instantiate from.
Instance Object The object to instantiate on each point on the point object. This can be overridden, on a per-point basis, by the instance attribute on the point object. In addition, it’s possible to do a delayed load of geometries, using the instancefile attributes. This is a string attribute that should contain an absolute path of any geometry file that can be loaded by Houdini. If motion blur is required, the companion attribute, instanceblurfile can be used. In that case, the instancefile attribute would be applied to shutter open, and this second attribute to shutter close.
Instance Transform Typically, the transform on the instanced object is combined with the object it’s being instanced by. This option allows you to turn off this behavior.
Point Motion Blur Specifies the motion blur behavior when rendering. Each point will have an instance of geometry. The transform of this instance is determined by the point’s position. Transformation motion blur on the instance is determined by the motion of the point. The motion of the points is controlled by this parameter.

No Motion Blur Do not perform motion blur.
Compute sub-frame geometry (deformation) Compute the point’s position by evaluating the geometry at sub-frame intervals. This can be problematic if the point count is changing frame to frame.
Use point velocity attribute The point’s vector attribute vis used to extrapolate the motion of the point. If using the delayed load attributes, velocity blur will be automatically assumed on the delay load geometry, if theinstanaceblurfile attribute is not given. In that case it is the responsibility of the user to tell the procedural the maximum length of the velocity vectors through theinstancefile_maxv float attribute. Otherwise clipping artifacts may occur.
Render Geometry as Bounding Boxes Only Don’t render the actual geometries, only their bounding boxes. This is useful for scene debugging and rendering quick tests.
CVEX Operator An optional path to a CVEX SHOP node. The point instancing will run this CVEX shader on each instance before rendering it. This allows you to set the transform for each instance procedurally.

The point instancing CVEX shader has a single output, a transform (xform) matrix.

The point instancing CVEX shader can use the following globals.

Name VEX Type Description
P vector World position of the point being instanced on
id integer ID of the point being instanced on. If the ‘id’ attribute already exists on the source object, it will be used. Otherwise the points will be numbered in sequence.
t float Shutter time (0-1)
obj_xform matrix Instance object’s transform
cam_xform matrix Camera’s transform
inst_bbox_minandinst_bbox_max vector The minimum and maximum corners of the bounding box of the instance geometry
inst_xform matrix The transform of the instance geometry

You can use dditional attributes of the points being instanced on. The available attributes are controlled by the CVEX Attribute Maskparameter.
CVEX Attribute Mask A glob to indicate which point and detail attributes should be copied into the CVEX context, if needed.

IFD Bounds

Bounding Box 边界框控制可以让你给引用的几何体指定一个边界盒。只有当此边界盒是“on screen”方式时，mantra才会加载引用的几何体。如果你设置Bounding Box 为 No bounding box required，这种情况下，Mantra会一直加载引用的几何体。你也可以在Sop Bound参数中引用SOP的边界框来指定边界框。
SOP Bounds 你想要引用其边界框的几何体
Min Bounds 边界框的最大维度，当明确设置了边界框时。
Max Bounds 边界框的最小维度，当明确设置了边界框时。
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