Maya MEL scripting how to read from an intField - scripting

Question

Forgive me for asking a basic question on stack overflow, but documentation and simple guides on the mel scripting language have proved to be very hard to find.
In any case, I'm trying to write a simple mel script that automatically creates a low-poly railroad, just as a learning excercise. The general idea is that a popup window will appear asking for how many segments you want
I've managed to get the window to appear, but now I have a few additional questions.
Firstly, how do I read in the value from the intField when I hit the button that runs the main procedure? I can't find any relevant guides.
Second, I've noticed a new problem in which the main script (which I'm currently running with a default value) seems to be running multiple times. What I think is happening is that when I click the button, I hold it down a bit too long, and Maya registers this as me clicking the button multiple times. How can I modify the button so that It only registers one click when I click on it?
Here is my code:
/***
Auto-Railroad Creator and Rigger
***/
// This script creates a low-poly, rigged railroad thingy that an artist can move and twist into position.
//relevant variables:
//the number of ties
int $numSegments = 0;
//the procedure that actually creates the railroad
//Heads up, this procedure is NOT finished. I'm just trying to get the window stuff working before I move on to completing this.
global proc makeRails(int $segments)
{
//If the given length is zero, do nothing.
if ( $segments == 0) return;
///the code proper
CreatePolygonCube;
polyCube -w 1 -h 1 -d 1 -sx 1 -sy 1 -sz 1 -ax 0 1 0 -cuv 4 -ch 1;
// Result: pCube1 polyCube1 //
return;
}
//The procedure that opens the popup window which asks for details:
global proc jh_makeRail()
{
//delete window if it already exists
if (`window -q -ex jh_makeRail`) deleteUI jh_makeRail;
//main window
window -topEdge 30 -title "Create a low-poly rail segment"
-mxb false -s true -rtf false -mb false -mbv false -w 300 -h 440 jh_makeRail;
//window content
columnLayout -adjustableColumn true;
separator -w 240 -h 20;
text -label "Utility to automatically create a low-poly rig for a simple railroad segment";
separator -w 240 -h 25;
text -label "Rail segment length (measured by the number of ties):";
intField -minValue 0;
//How do I use the value of this intField?
separator -w 240 -h 20;
//Since I haven't figured out how to read in the value of the intField, I'm using a default value of 30.
button -label "Make Rail" -c "makeRails 30";
window -e -w 300 -h 500 jh_makeRail;
showWindow jh_makeRail;
}
//This here is supposed to be the "entry point" of the mel script, where the code starts doing things.
jh_makeRail;

Answer 1

So, good news. A kind person on reddit helped me solve the problem.
First, regarding the secondary procedure running twice... turns out I was wrong about that. It was making two cubes because I told it to.
I had believed that "CreatePolygonCube;" and "polyCube -w 1 -h 1 -d 1 -sx 1 -sy 1 -sz 1 -ax 0 1 0 -cuv 4 -ch 1;" were two parts of the same instruction, but they are actually two different ways to make a cube.
Next, regarding the primary question... Transfering the value from the intField to a global variable involves some sort of shuffling.
The code this person suggested is as follows:
{
//You need to declare existing global vars in like this, almost like you're importing them into the proc
global int $numSegments;
//Create field
string $myIntField = `intField -minValue 0`;
//build command string
string $cmd = "$numSegments = `intField -q -value " + $myIntField + "`";
//set change command
intField -edit -changeCommand $cmd $myIntField;
}
(This is a part of the window function, not the whole thing.)
The relevant thread is here:
https://www.reddit.com/r/Maya/comments/q1vz1i/i_need_help_with_mel_scripting/hfjpoh7/?context=3

Answer 2

global int $numSegments;
Yeah, don't do this :)
Use the optionVar MEL command instead!
// define some custom name for your global variable
string $myName = "railroad_num_segments";
// set your global var like so:
global void railroadSetNumSegments(int $num) {
optionVar -intVal "railroad_num_segments" $num;
}
// and query the value like so:
global int railroadGetNumSegments() {
// check to see if we have previously registered the optionVar
if(!`optionVar -exists "railroad_num_segments"`) {
// if the option doesn't exist, define a 'sensible' default here
railroadSetNumSegments(1);
}
// return the user preference
return `optionVar -q "railroad_num_segments"`;
}
The advantage of optionVar is that your user preference is now stored between Maya sessions.
Whenever you need the number of segments in your script, simply call railroadGetNumSegments().
You can also simplify the intField control to just:
intField -minValue 0 -value `railroadGetNumSegments` -changeCommand "railroadSetNumSegments #1";
Specifying #1 in the change command, will automatically query the controls value when it changes.
Also worth noting that there are actually 3 ways to create a polyCube in Maya. The entirely manual approach would be:
use createNode to create the polyCube node, and a mesh node.
use connectAttr to connect the outMesh attribute of the poly cube node, to the "inMesh" attribute on the mesh node.
use the sets command to add the mesh to the default shading group set.
use setAttr to set the polyCUbe node params to the desired values
That is in effect what the polyCube MEL command does internally.
The "CreatePolygonCube" command uses optionVar, to read all of the user preferences for the default widths/heights/num divisions etc; and then passes those parameters to the polyCube command.