INSTALLATION:
Execute this command in the MEL command-line (it will return the maya application directory):
internalVar -uad
return value example on a Windows machine
//Result: C:/Users//Documents/maya/
Then create a directory called "plug-ins" without quotes inside the returned folder and copy the "prAttractNode.py" file inside. Example on a windows machine:
C:/Users//Documents/maya/plug-ins
The final plugin file path would be:
C:/Users//Documents/maya/plug-ins/prAttractNode.py
This way you can use this plugin in different maya versions and in different OS as it is a scripted plugin and not a compiled one. You say you use Maya 2013 but you do not say what OS you are using.
Optionally, if you want to use the provided compiled versions (those files ending with .mll, only usable on windows) you can create a "plug-ins" folder inside your maya version folder (2013) and copy the appropiate plugin version there (prAttractNode.mll)
example folder on a windows machine:
C:/Users//Documents/maya/2013-x64/plug-ins
The final plugin file path would be:
C:/Users//Documents/maya/2013-x64/plug-ins/prAttractNode.mll
USAGE:
To use the tool from a shelf button paste the following code in the MEL command-line or Script Editor:
loadPlugin -quiet prAttractNode;prAttractNode
Then select it and Middle-Mouse drag this on your selected shelf. Select MEL type. That's it. You can use the plugin by clicking this button. Just follow usage instructions on the plugin page.
