These are a few basic CHOP techniques. This is Tscript-focused and requires a python makeover.
Getting RGBA values between TOPs and CHOPs
The CHOP to TOP gets pixel values quickly back into TOPs.
Getting XYZ values between SOPs and CHOPs
The SOP to CHOP is used to get the XYZ values in a SOP's points into the channels of a CHOP, where they can be edited with CHOPs. All point attributes in a SOP can be obtained, including user-defined point attributes.
The CHOP to SOP is used to get values in CHOP channels into the points of a SOP. The CHOP to SOP takes a geometry at its input, and without changing the surface type or connections between vertices of polygons or meshes, it modifies point values only. It operates much more quickly than the Point SOP.
Any point attribute can be replaced by values in CHOP channels.
In both cases, point groups in SOPs can be used to restrict the data being transferred between SOPs and CHOPs.
Speeding Up CHOPs using the Performance Monitor
Diagnosing CHOPs with the print() Function
Sometimes it unclear what value a CHOP parameter may have when it is cooked, if it is an expression. You can put the expression in a print() function, and it will display its value when it evaluates. The syntax is
print(string, expression) where string is printed in front of the value on the standard output.
Multiple Objects and CHOP Networks
Sometimes you want one CHOP network to drive one object. You may want to clone the pair dozens of times, but you may want each to behave a bit differently. So you want to get a number in each of the objects and CHOP networks that identifies it.
If you could get the digits in the object name and the CHOP network name, you could use this number to identify the unit. But there is no obvious way of getting that number into CHOP or object parameters. Here is a way:
The expression function,
opdigits() gets the numbers that are in an OP name. For example, it extracts the 23 from an OP named leg23left .
This allows you to make one CHOP network for each of 100 similar characters. For example, in a CHOP, you can get the number of the CHOP network by using these functions:
opname("..") = "ch1" (a string)
opdigits("..") = 1 (a set of digits)
opdigits("opname") returns the numeric value of the concatenation of all the digits in a node's name. It is used when building several similar networks. For example: opdigits("/obj/geo7") = 7
opdigits("..") = 7 (at the SOP level of geo1)
In the 100 objects geo1 to geo100, you can use the expression:
You can use this function in the Random Seed parameter in the Noise CHOP, which will generate a different noise curve for each CHOP network.
The Use of CHOPs in Managing Large Projects
You can hold many moves for many characters in one CHOP network and examine any CHOP by connecting it to a character immediately. So it acts as a library and viewer of moves. Also, when several animators work on one project and the goal is to make the character have similar behavior from scene to scene, animators can pick moves from the library to start with. This is like a library of materials that keep the rendered look the same from scene to scene.