Expressions And Time (2)

[ljilekor]

How to query an attribute's value at a specific time inside an expression and keep the result INTERACTIVE?

I can not use 'getAttr -t MYTIME obj.attr' nor 'keyFrame with the -eval flag' nor eval() in my expression because I want the expression to be interactive. (so I need to use the dot notation for expressions)

I'm afraid there's no other sollution (except diving into the API) than using the dot notation for expressions.
So, is there somekind of specific dot notation that queries an attribute at a specific time inside an expression?
ex. obj.attr[MYTIME] or obj.attr@MYTIME or obj.attr(MYTIME)

Thx

[joojaa]

You can't. you really cant do it with the api either (without very serious development time of MONTHS) witout going into the a same problem getattr -t has. You can keep the thing interactive even if you use getattr -t tough as long as you have trigger.

However you DONT want to do this. instead you wamnt eiter to use a clone of the data or a cahced version fo the data.

[ljilekor]

Thx, at least I know I can't directly...

QUOTE(Joojaa)
You can keep the thing interactive even if you use getattr -t tough as long as you have trigger.

Could you give me a little example please.

Thx for your concern.

[joojaa]

Expressions arent mel but they do parse and execute them it however needs a connection is need to trigger it And a output MUST be affected, this is easy to fool. all you need is to read a input for change and put a output in between and after you can do whatever you wish and it gets executed every time you change the input.

However your in for a much more philosophical problem, which is how maya WORKS without thsi feature you couldn't animate anything. See moving a object does NOT change its past, it just affects its current state, its past gets changed ONLY once you keyframe the changes. So its logical that you can ask what the value is at any given moment, however also it follows that you cannot get an anwser untill the function at that time has changed. Ofcourse you can turn auto keyframe on but thats not very useful for most users. Likewise api can't dent this design, in theory tough it could keep copies of the anim curves that it does AUTO keyframe on change tough to report you the value of what it WOULD be if keyed. But its not entirely ideal but by far the right way to go.

Offcourse the expression can also set the keyframe! Wich would accomplish the same thing but much more interactively, but also witha lot of undo problems unless you disable undo at start of each setkey.

[ljilekor]

Thx Joojaa

That's probably why I can't find any TransformChanged event within the scriptjobs. I was looking into scriptjobs to trigger the MEL function that handles the getAttr -t MYTIME obj.attr commands (there's a lot of them).

I guess it's somehow an overkill to use the idle event. But there may be other scriptjob events/conditions that I could use to trigger my 'updateTimes' function... I'm just not sure when exactly the scriptjob will trigger the 'updateTimes' function

• attributeChange
• autoKeyframeState
• ManipsExists

are possible candidates. I'll check it out.

Hope I'm on the right track

Thx 4 everything

[joojaa]

You cannot use scriptjobs if you want the data to be affected during animation. Sicne scriptjobs dont exsiust during playback.

[joojaa]

Oh by the way could yeou actually describe WHAT exactly your are doing then it makes it easier to help you. Maybe we can make a totaly different strategy (it is totaly clear that if somebody eeds to use getattr .t inside maya expreessions or scriptojes they are essentially doing something wrong)

[ljilekor]

All other apps I worked with (Max, LW , XSI, C4D, Messiah, ..) enables me to query any attribute/channel at any given time in one or the other way. Thats why I had difficulties to 'believe' that Maya couldn't do this fairly simple and common task at first. Of course that's before you(Joojaa) confirmed this.

I'm building a huge tentacle FK/(spline)IK setup that has to be as versatile as possible. I'm working with 'animators' not 'simulators', so I'm keeping as far away from any kind of simulation. We need full control over the tentacles' poses. The director is too picky.

The tentacle blends from IK->FK from the bottom up too the tip. Everything is animatable/blendable. It enables us to animate the base with or along a curve and to pose an variable portion of the tip in FK.
The setup is great, easy, fast to 'work' with and does exactly what is expected, without bothering the animators with the underlying technical stuff. A lot of shot specific tentacles can be created easily with asimple GUI.

So all of it works perfectly and fine... but... the lag between the bones in FK.

A tentacle has +-150-300 bones (depending on the needs). In order to simplify the number of controls, A control is created every (let's say) 15 bones, that controls the 14 following bones.
A LAG attribute, found on the Control itself, controls its 14 descendents by a simple expression that adds lag (now with getAttr).

I repeat: 'Everything works fine.'

The 'only' problem is that the user needs to scrub (or press a custom GUI button) to 'preview' his pose. He cannot manipulate the contol and see the result interactively... That's a real b#*h.

It would be a real shame to throw away all that fine working, precise and time saving stuff. So, it may be a little late to completely change the approach.
If adding lag can't be automated (still have trouble 'believing' it since it's soooo simple in theory'), we'd choose the option to add lag by 'animating' it manually (that's what we do ).

A sollution to automate lag could be:

CODE
int $job1= scriptJob -ac joint1.rz myfunc;

global proc myfunc()
{
    float $frame=currentTime -q;
    float $poo=getAttr -t ($frame-5) joint1.rotateZ;
    setAttr  joint2.rz $poo;
}

It refreshes the tentacles' pose everytime the user releases the manipulator. It's not 'interactive' in the pure sense but we can live with that. But, AAAAAAAAAAARRRRRRRRRGGGGGGGGHHHHHHHH #&**!!$#... . Like you said: scriptjobs dont exsist during playback. I could combine it with a changeTime(or something) event... I guess...

I understand the complexity a 3D app has to deal with and I may be a little indoctrinated by having used other apps in the past. But not being able to do something that simple and straightforward is a serious dent in Maya's architecture. But, no stress. I also have eyes for its arsenal of advantages enabling us to tweak to infinity (and beyond)

Anyway, it's great to have somebody like you(Joojaa) to help getting trough the thick stuff.

[ljilekor]

QUOTE(Joojaa)
Expressions arent mel but they do parse and execute them it however needs a connection is need to trigger it And a output MUST be affected, this is easy to fool. all you need is to read a input for change and put a output in between and after you can do whatever you wish and it gets executed every time you change the input.

Is it possible to give me a little step by step example of this please?