+ Chapter 02 - MEL - Script Editor +
Instructor - Pradeep Mamgain
+ Overview +
Most of the time while creating MEL scripts, you will be writing and executing scripts inside of Script Editor. You can use script editor to cut and paste the whole scripts and execute them at once. All the operations you perform in the Maya interface are also recorded as MEL commands in the script Editor.
MAYA, MEL & PYTHON
Maya now supports Python. Python is simple, elegant and high level language. A language that is great for novices as well as for hard-core programmers. It can handle network programming, XML and databases. It also uses most powerful third-party modules. You can execute mel commands within Python in Maya. Almost all the MEL commands can be used within Python. However, Python syntax is quite different from that of MEL. There are certain MEL built-in functions that are not available in Python. Math function like abs, sin, cos.. etc and string functions like match, gmatch.. are not available in Python. However Python includes several libraries that can perform these functions.
Python syntax is different from MEL. For example MEL command "sphere -name mySphere;" would be re-written for Python as
import maya.cmds as cmds
cmds.sphere (name ="mySphere")
In order to enable MEL commands inside Python you must enter following line at the start.
import maya.cmds
You can automatically import MEL commands in Python by saving a Python script in Maya's script path.
We are making a series of tutorials on using Python inside of Maya, so we request you to kindly get registered in the Forums. It would help us in informing you that when this series would be available on CG Sutra.
There are three ways to enter and execute the MEL commands.
- The Command Line.
- The Command Shell.
- The Script Editor.
+ The Command Line +
The command line allows us to quickly execute MEL commands one at a time. The command line is located at the lower bottom part of the interface. From there you can execute MEL as well as Python commands. Click on the interface where MEL is written, you can now toggle between MEL and Python command line.
Figure 2.1 - MEL Command Line.
If command line is hidden, you can make it visible by selecting Display > UI Elements > Command Line.
Figure 2.2 - Display Command Line, if hidden.
+ The Command Shell +
Open the command shell from Window > General Editor > Command Shell.
Figure 2.3 - Open Command Shell.
Command Shell is something similar to DOS prompt. We will not explore it more as Script Editor is the most efficient medium for creating and executing MEL commands.
Figure 2.4 - Command Shell Window.
+ The Script Editor +
The Script Editor can be accessed by choosing, Windows > General Editor > Script Editor or click the Script Editor button in the bottom right of the main Maya window.
Figure 2.5 - Script Editor Button
Figure 2.6 - Script Editor Window.
For a brief description of Script Editor, see Figure 2.7.
Figure 2.7 - Script Editor Functions.
From Edit menu, you can access all standard windows menu commands like Undo, Cut/Copy, paste, Select All and Search and Replace.
Figure 2.8 - Edit Menu
Almost every command Maya executes echoed in the history area. This is a great option to learn whats going on behind the curtain. By default, Maya only echoes commands that it thinks significant, however you can override this option by choosing History > Echo All Commands from the editor's menu.
Line numbers in errors and Show Stack Trace aid in the debugging of the scripts. Show Stack Trace is useful when you run inter-dependent scripts. It opens another window which lists errors and their line numbers in external script files. Batch render Messages when turned on, Batch render messages are displayed in the Script Editor. From History Output, you can choose whether you want output for MEL, Python or Both. Next set of commands is for suppressing the output. When you executed a command Maya displays a Command result, for example when you execute MEL command,
sphere -name mySphere;
Maya will echo following command result in the Script Editor.
// Result: mySphere1 makeNurbSphere2 //
You can also suppress Info, Warning and Error Messages. When Suppress Stack Window is turned on and Show Stack Trace is also enabled, results are returned to the output window instead of a separate stack window.
Figure 2.9 - History Commands.
You can create as many tabs, as you require. Click on New Tab to make a new tab. Tabs can be renamed and deleted from the command menu. Show quick help, displays a small window on the right bottom side of the editor. In the search box, type the command, for example, file. Editor will show quick list of parameters used with file command.
Figure 2.10 - Command Menu. Figure 2.11 - Quick Help
Other way of enabling quick help, is to double click on the keyword and right click; from the marquee menu select quick help. Script Editor will open quick help panel for you in the right bottom corner of the editor, as seen in Figure 2.11A..
Figure - 2.11A, Quick Help, Alternative way.
For see detail documentation, right click on quick help and select Show Command Documentation, as shown in Figure - 2.11B.
Figure - 2.11B, Displaying full command documentation.
+ How to get Help with MEL? +
One way of getting help you already know, as described above. Maya's help system is so extensive and powerful. You can get help on almost all MEL commands. Execute following MEL command.
Example 2.1 - Getting help on help.
help help;
The command output you will get in the script editor will be something as follows..
Example 2.2 - help command result.
help help;
// Result: Synopsis:
help [flags] [String]
Flags:
-q -query
-doc -documentation
-l -list
-lng -language String
-pdt -popupDisplayTime UnsignedInt
-pm -popupMode on|off
-ppt -popupPauseTime UnsignedInt
-rm -rolloverMode on|off
Above output is about getting help on help. Now if you want to see the documentation of the file command. Execute following command..
Example 2.3 - help command with -doc parameter.
help -doc file;
This will open your default browser and display file command documentation, as shown in Figure 2.12.
Figure 2.12 - file MEL command Documentation.
You can access whole MEL command reference from Help (Maya Main Menu) > MEL command reference. Here you can browse the commands by category wise or alphabetically. A search text box is also available to search the command reference.
+ What Next +
Now we have understanding of how script editor works; in next chapter we will discuss about the MEL command and its syntax.
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