How To Write Something That Responds To "events" In Maya

[yunjun]

I want to write a plugin that can respond to user action. say, for example, when the user selects an object, the plugin can output its name/attributes; or when the user select a different frame (changing the current time), the plugin does something automatically (e.g. create a sphere). I know how to write commands that need to be executed from the Scripter Editor, but not the ones that respond to certain events. Can anyone give me an idea? Thanks!

[rob-bateman]

MMessage, or scriptJob in mel. There is also scriptCtx and MPxContext if you want to start adding custom selection based tools.

[yunjun]

Thank you for your advice! I looked into the documentation and found the MEventMessage class with addEventCallback will possibly solve my problem.

The scriptJob -timeChange(-tc) script will also work. but the comment says "The script will not be executed if the time is changed by clicking on the time slider, whereas scripts triggered by the "timeChanged" condition will be executed."

But don't users always like clicking on the time slider to change the current time? I am not sure if this comment will also have effect on the MMEventMessage::addEventCallback, because the parameter passed to this function is the same as the scripJob attributes. Will try.

[yunjun]

One key question:

Where do I put the code? Ｉ　ｍｅａｎ　ｔｈｅ　ｉｍｐｌｅｍｅｎｔａｔｉｏｎ　ｏｆ　MEventMessage．

Don't I always start my plugin by implementｉｎｇ a
class myCmd : public MPxCommand
{
........
}

??
This means I　ｓｔｉｌｌ　ｎｅｅｄｓ　ｔｏ　ｔｙｐｅ　ｉｎ　ｔｈｅ　ｃｏｍｍａｎｄ　ｉｎ　ｔｈｅ　ｓｃｒｉｐｔ　ｅｄｉｔｏｒ　ｒａｔｈｅｒ　ｔｈａｎ　ｔｈｅ　ｐｌｕｇｉｎ　ｒｅｓｐｏｎｄｉｎｇ　ｂｙ　ｉｔｓｅｌｆ？

[yunjun]

Hi, maybe I wasn't very clear in my last post. I mean, if I want something running in the background that responds to user events, such as changing current time or selecting objects, how can I achieve this? the MPxCommand runs only when the user types in the command in the script editor, but not "listening to" what's happening in the scene.

Thank you!

[ryan47]

QUOTE(yl2000 @ 11/20/07, 05:45 AM) [snapback]276715[/snapback]
Hi, maybe I wasn't very clear in my last post. I mean, if I want something running in the background that responds to user events, such as changing current time or selecting objects, how can I achieve this? the MPxCommand runs only when the user types in the command in the script editor, but not "listening to" what's happening in the scene.

Thank you!

Hi yl2000,
First, we may define some functions which are responsible for each specified event respectively.
Then, we need to tell the system their association by "add*Callback" functions in "M*Message" classes.
After we invoke "add*Callback", system would listen to the events and dispatch them to the functions we associates before.

(M*Message stands for all related Message classes in Maya, such as MEventMessage, MDagMessage, MModelMessage, ... etc.)

In your case, you could invoke "add*Callback" in the "doIt()" procedure of your derived class. Then, after user execute your command, the system would start to dispatch the events to the associated function you defined.

Hope this helps~
Ryan47

[joojaa]

Ok theres the thing, mayas not really event based, or rather maya is depends on how you look at things. Idea here is that maya does not in general sense broadcasts its real events much at all since they are handled by the graphing system.

So it depends on what you do, if your building a gui of some kind then api is not the basis for most of that, on the other hand if yu want maya interactivity you want to build nodes instead.

[rob-bateman]

QUOTE(yl2000 @ 11/16/07, 12:12 PM) [snapback]276612[/snapback]
Where do I put the code? Ｉ　ｍｅａｎ　ｔｈｅ　ｉｍｐｌｅｍｅｎｔａｔｉｏｎ　ｏｆ　MEventMessage．

see the little robthebloke link in my sig..... it has examples.

[yunjun]

Thank you guys so much for leaving me these great advices. I will try your suggestions out later today and I am sure they will be very helpful.
Thank you, Rob Bateman, I will look into your examples!

[yunjun]

QUOTE(Rob Bateman @ 11/20/07, 04:32 AM) [snapback]276748[/snapback]
see the little robthebloke link in my sig..... it has examples.

Hey, Rob Bateman,

I am trying the examples on your website. The MEventMessage1 doesn't link on my computer, it says:
CODE
Main.obj : error LNK2019: unresolved external symbol __imp__glEnd@0 referenced in function "void __cdecl IdleFunc(void *)" (?IdleFunc@@YAXPAX@Z)
1>Main.obj : error LNK2019: unresolved external symbol __imp__glVertex2i@8 referenced in function "void __cdecl IdleFunc(void *)" (?IdleFunc@@YAXPAX@Z)
1>Main.obj : error LNK2019: unresolved external symbol __imp__glBegin@4 referenced in function "void __cdecl IdleFunc(void *)" (?IdleFunc@@YAXPAX@Z)
1>Main.obj : error LNK2019: unresolved external symbol __imp__glOrtho@48 referenced in function "void __cdecl IdleFunc(void *)" (?IdleFunc@@YAXPAX@Z)
1>Main.obj : error LNK2019: unresolved external symbol __imp__glLoadIdentity@0 referenced in function "void __cdecl IdleFunc(void *)" (?IdleFunc@@YAXPAX@Z)
1>Main.obj : error LNK2019: unresolved external symbol __imp__glMatrixMode@4 referenced in function "void __cdecl IdleFunc(void *)" (?IdleFunc@@YAXPAX@Z)
1>Debug\myCmd.mll : fatal error LNK1120: 6 unresolved externals

I included glut32.lib glui32.lib in the input of my linker, but your code has and included at the beginning. I am not sure why it doesn't link. I usually use glut.h only. On the openGL site, it says:
CODE
A GLUT source file should:
#include
Non-GLUT source files should:
#include
#include

I don't even understand what it means. How can I solve the problem? Thank you.