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Recursive functions with MAXScript

Summary: This document demonstrates recursion in MAXScript using a simple recursive function.

Product(s)	Release(s)	Platform(s)
3D Studio MAX (TM)	2.0; 2.5	Win95, WinNT
3D Studio VIZ	2.0	Win95, WinNT
Audience:	For Public Distribution - Global
Keywords:	RECURSIVE FUNCTION MAXSCRIPT 5489
Related documents:		None
Document: US-XT-TD805489.DOC	Revision: A
Creation date: October 13, 1998	Last revised: December 11, 1998	Expires: January 31, 2000

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Overview

A recursive function calls itself within its own definition. This means that one of the lines in the MAXScript function definition calls the function again; creating a "picture within a picture within a picture" effect.

Recursive functions are appropriate for working with hierarchies and groups, or any collection whose contents might have additional elements beyond the first collection loop. For arrays and pathname collections, iterative functions are usually more appropriate. In this document both iterative and recursive functions will be defined, but the discussion focuses on recursive functions.

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Note: For more information on "mapped" or iterative functions, search the MAXScript Reference, index tab for "Function Definition."

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Before creating the recursive function, you must create some objects for the script to work with. Go to the Utilities panel, push the MAXScript button, and then push the ‘New Script’ button from the MAXScript rollout. Copy and paste the following text into the new MAXScript window:

resetMaxFile #noPrompt

--Make some scene objects

spheres = for i in 1 to 10 collect
sphere radius: (i*10) position: [(10*(1.0*i)^2) - 10, 0, 0]

--A function to link all the objects in an already defined array:

fn SimpleLinkArray Array = 
(
for i = 1 to Array.count do
    (
        if Array[ (i+1)] != undefined then
        Array[ (i+1) ].parent = Array[i]
    )
)

--Call the function

SimpleLinkArray spheres

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Tip: Evaluation will run the entire script. To evaluate one line of the script at a time, place the cursor at the end of that line and hold the <SHIFT> key while pressing <ENTER>. To evaluate multiple lines, highlight the lines and press and hold <SHIFT> while pressing <ENTER>.

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Note: While the recursive functions defined below can be evaluated on any linked objects, it is recommended that you use the objects created by the script to avoid confusion. To create fresh objects at a later point, evaluate the code above by highlighting the block of code and pressing <SHIFT> and <ENTER> simultaneously.

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Next, you will make a script that randomly "squashes" the spheres. To do this, copy and paste the following text into "Simple Recursion" window, after the existing code:

--Now make the recursive Script

fn Stretcher arg = 
(
addModifier arg (stretch stretch:0.0)
animate on
    (
    at time 0 (arg.stretch.stretch = random 0.0 -.25; 
arg.stretch.amplify = 0.0)
    at time 100 (arg.stretch.stretch = random -1.0 -2.0; 
arg.stretch.amplify = -20.0)
    )
for i =1 to arg.children.count do 
    (
        Stretcher arg.children[i]
    )
)

Stretcher $sphere01

Script analysis

resetMaxFile #noPrompt

---

Tip: "Commenting out" is a method of including text in code that the program will ignore. This is useful for commenting on lines of the code as you write it, and for disabling parts of a routine without deleting the code. In MAXScript, the comment symbol is two hyphens. [ -- ]. MAXScript ignores whatever follows the two dashes as it evaluates that line of code. Comments will only apply to one line of code. 

---

fn SimpleLinkArray Array = 
(
for i = 1 to Array.count do
    (
        if Array[ (i+1)] != undefined then
        Array[ (i+1) ].parent = Array[i]
    )
)

fn Stretcher arg = 
(
addModifier arg (stretch stretch:0.0)
animate on
    (
    at time 0 (arg.stretch.stretch = random 0.0 -.25; 
arg.stretch.amplify = 0.0)
    at time 100 (arg.stretch.stretch = random -1.0 -2.0; 
arg.stretch.amplify = -20.0)
    )

for i =1 to arg.children.count do 
    (
        Stretcher arg.children[i]
    )
)

Stretcher $sphere01