This node empowers users to implement their own callbacks using the VEX language. Each input and output port is accessible as a variable in the VEX snippet. The port names dictate the names of the bound variables. In the VEX snippet, users should read from the input variables, perform the user-defined calculations, and write the results to the output variables.

The example VEX snippet below calculates various properties of a circle:

diameter = 2*radius;
circumference = 2*M_PI*radius;
area = M_PI*radius*radius;

A few notes about this snippet:

• The constant ‹M_PI› is available because “math.h” is implicitly included for convenience.

• The snippet writes to three undeclared variables - ‹diameter›, ‹circumference›, and ‹area›. These are the names of the node’s output ports. They are accessible because the node binds the output ports to variables of the same name.

• The snippet reads from the undeclared variable ‹radius›. This is the name of the node’s input port, so it is bound to the variable of the same name. The input variables are read-only, so an error is generated if an attempt is made to assign it a new value.

The graph below reads the radius from the graph input node, calculates the circle statistics, and writes the results to the output.

In order for the RunVex node to function, it needs to know the type of its input and output data. When the ports on the RunVex node are connected, it uses the connection to determine the data type of its input and output ports. The ports will also change color to reflect the type of the connected data.

However, there are nodes like the graph input and output nodes that have variadic ports that accept or produce different types of data (these ports have a gray color). When such a gray port is connected to the inputs and outputs ports on the RunVex node, RunVex does not have enough information to know the type of variable to produce in the VEX context. In this scenario, the type information needs to be made explicit with the use of a Value node. In the example above, the Value<Float> nodes in the graph allow the RunVex node to recognize the data type of the variable it is binding.