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Double-click this node to build a VOP network inside.
(Alternatively, you can specify a SHOP node containing the VOP network,
or specify a
.vfl file containing the CVEX program.)
The VOP network runs in the CVEX context, not the SOP context. This means SOP specific VOPs and VEX operations are not available. Instead use the From File variants and the provided operator input strings.
This node modifies geometry attributes.
Create Parameter VOPs with the names of attributes to specify inputs. Set a parameter as "exported" to allow writing to/creating the corresponding attribute.
Where to get the program to modify attributes.
Use a VOP network inside this node.
Use SHOP node containing a CVEX VOP network. Specify the node in the SHOP path parameter.
This can also point to any node that contains a CVEX VOP Network.
Referenced nodes parameters will be used.
Use a file containing a CVEX program. Specify the file path in the Script parameter.
A SHOP node containing a CVEX VOP network, when VEX source is SHOP.
A path to a file containing a CVEX script, when VEX source is Script.
Re-load VEX Functions
When VEX source is Script, reloads any
.vex files to
account for changes made outside of Houdini.
When VEX source is Myself, the command line Houdini uses to compile the VOP network inside this node.
When VEX source is Myself, recompiles the VOP network inside this node.
Evaluation Node Path
VEX functions like
ch() usually evaluate with respect to this node.
Enter a node path here to override where the path search starts from.
This is useful for embedding in a digital asset, where you want searches
to start from the asset root.
When a VEX parameter is exported, the bound attribute will be created if it doesn’t exist. This pattern can be used to override the export option on the VEX shader to avoid writing to or creating certain attributes. The pattern matches the VEX parameter, not the bound attribute. The attribute will still be bound for reading.
There should be no threading issues with VEX. In the unlikely event that there are, this will allow you to determine which node is guilty, and work around it without turning off threading on a global scale.
Only run the VOP network on this group in the input geometry. Leave this blank to modify all the input geometry.
What the group is made of.
What class of geometry attributes to modify. No attributes will be bound, except read-only detail attributes, when set to Numbers.
Iteration count when Run Over is set to Numbers.
@elemnum will be the iteration number from 0 (inclusive), to this number (exclusive),
@numelem will be this number.
No attributes will be bound when in this mode, except read-only detail attributes.
Thread Job Size
Maximum number of iterations run at a time in any thread when Run Over is set to Numbers. If this is greater than or equal to Number Count, the VEX code will run single-threaded. If each iteration will take a very large amount of time, set this to 1. However, there is quite often a significant advantage to making this value larger, especially if each iteration will take a small amount of time, and if any work can avoid being duplicated by running multiple iterations at a time.
Autobind by Name
Automatically bind attributes to parameters by name. If for some reason you need CVEX parameters to have different names than the corresponding attributes, turn this off and use the Number of bindings parameter to set up mappings between Attribute name and VEX parameter.
Integer attributes will bind to integer parameters. Float attributes will bind to float, vector, point, matrix, or matrix4 depending on their tuple size. String attributes will bind to strings.
Autobind Groups by Name
Automatically bind any groups to the integer parameter prefixed with
Update Normals If Displaced
If points are being run over, and the
P attribute is written to,
N attribute is not written to, any incoming normals will
become out of date. When this option is set, vertex and point
normals will be updated when this occurs.
Attribute to Match
@opinputinputnum_name syntax lets you get the value of an attribute from the corresponding element on another input. If this parameter is blank, the "corresponding" element is the element with the same index (e.g. point number) as the element the node is currently processing. If you specify the name of an attribute, the "corresponding" element is the element that has the same value in the named attribute as the current element. See accessing attributes from other inputs on the VEX snippets page for more information.
For example, if you used
id as the "attribute to match", and you were processing a point with attribute
id set to
@opinput1_P would give you the
P attribute on the point in the second input that also has
id set to
Compute Results In Place
When compiled the Attribute VOP is able to work on the incoming geometry in place without making a copy of it. This can speed up processing as one less copy is made, but requires that the VEX code doesn’t bind for writing any attributes that are read from the first input.
Output Selection Group
The name of a group to use as the output selection. When the highlight flag is enabled for this node, this group will be the output selection used by later modeling tools (if it exists).
The following examples include this node.
This example uses static object nodes in an RBD simulation of a grid falling and bouncing off three spheres before it hits the ground.
This example demonstrates various ways in which you can use a solver node to transform an object based on ordinary differential equations.
There are 6 different solvers in this example. There is also the exact answer as a point of reference. The solvers are numerical methods that solve the following coupled Ordinary Differential Equations with initial conditions:
x' = y ; x(0) = 1 y' = -x ; y(0) = 0
The numerical methods for Ordinary Differential Equations are: Forward Euler, Runge-Kutta Second Order, Runge-Kutta Third Order, Runge-Kutta Fourth Order, and Parker-Sochacki solved two ways. In one version, Parker-Sochacki is hard coded at order 5. In another version Parker-Sochacki is written in a for loop where the order can be adjusted by the user.