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Lights: Lookat Node Vs Aim Constraint

Tags: #<Tag:0x007f1935abf9c8>

user_deleted 2007-06-21 20:08:15 UTC #1

I feel I am trying to do something that is fairly straight forward but am hitting some walls with Maya.

This is not an aimVector question.

I am trying to setup a simple light aim constrained to a locator so I can move the locator and the light is always looking at the locator. Simple enough. This can be done 2 ways, niether of which is working how I want:

Aim Constraint
- When looking through the light and orbiting, the light will often gimbal lock and flip. this makes it very difficult to 'nudge' a light just a little.
- Dollying is not possible when looking through the light camera as you can with a lookAt node.

lookAt node (This is what is used when you do a 'Create -> camera -> Camera and Aim')
- Dollying (alt MMB) possible when looking through light
- No gimbal lock when orbiting about locator and looking through light camera.
- When the locator is moved, and then you orbit while looking through the light camera, you now get an annoying 'snap' every time you move the light. The light is looking at the old location of the locator until you mouse up.

I would love to be able to set it up so that it acts like a lookAt node, but without the snapping. This is killing me and I would love any ideas....

In case you are interested here is some mel for creating each version:

CODE
global proc string[] createAimLocator(string $xform)
{
  string $locatorShapeList[] = spaceLocator -p 0 0 0;
  string $locatorShape = $locatorShapeList[0];
  // Make sure we are operating on the transform
  if ( "transform" != nodeType $xform ) {
    string $parents[] = listRelatives -parent $xform;
    $xform = $parents[0];
  }
  string $aimList[] = aimConstraint -offset 0 0 0 -weight 1 -aimVector 0 0 -1 -upVector 0 1 0 -worldUpType "vector" -worldUpVector 0 1 0 $locatorShape $xform;
  return {$locatorShape, $aimList[0]};
}

string $light = spotLight;
createAimLocator($light);

CODE
string $light = spotLight;
if ( "transform" != nodeType $light ) {
string $parents[] = listRelatives -parent $light;
$light = $parents[0];
}
string $locatorShapeList[] = spaceLocator -p 0 0 0;
string $locatorShape = $locatorShapeList[0];
string $target = $locatorShape;
string $lookAt = createNode -name ($light+"\_group") "lookAt";

setAttr ".aimVector" -type double3 0 0 -1;

connectAttr ($target+".tx") ($lookAt+".target[0].targetTranslateX");
connectAttr ($target+".ty") ($lookAt+".target[0].targetTranslateY");
connectAttr ($target+".tz") ($lookAt+".target[0].targetTranslateZ");
connectAttr ($target+".rp") ($lookAt+".target[0].targetRotatePivot");
connectAttr ($target+".rpt") ($lookAt+".target[0].targetRotateTranslate");
connectAttr ($target+".pm") ($lookAt+".target[0].targetParentMatrix");

connectAttr ($light+".pim") ($lookAt+".constraintParentInverseMatrix");
connectAttr ($light+".t") ($lookAt+".constraintTranslate");
connectAttr ($light+".rp") ($lookAt+".constraintRotatePivot");
connectAttr ($light+".rpt") ($lookAt+".constraintRotateTranslate");

connectAttr ($lookAt+".constraintRotateX") ($light+".rotateX");
connectAttr ($lookAt+".constraintRotateY") ($light+".rotateY");
connectAttr ($lookAt+".constraintRotateZ") ($light+".rotateZ");

connectAttr ($lookAt+".distanceBetween") ($shapes[0]+".centerOfInterest");

joojaa 2007-06-23 19:32:23 UTC #2

QUOTE
- When the locator is moved, and then you orbit while looking through the light camera, you now get an annoying 'snap' every time you move the light. The light is looking at the old location of the locator until you mouse up.

Its a update issue, it affects all view moves, ie they update only the one view for increased performance on that view. Same effect can bee seen by looking at neighboring view port if you move lights in light mode.

theres a mel commend that sets this behaviour on and of you can try forcing the refresh on. Just cant rembere the command offhand.

user_deleted 2007-07-10 20:46:48 UTC #3

QUOTE
Its a update issue, it affects all view moves, ie they update only the one view for increased performance on that view. Same effect can bee seen by looking at neighboring view port if you move lights in light mode.

Thanks for the reply Joojaa. The snap is happening in the active viewport so I am not sure that it is an update issue. When the target is moved, the light acts like it looses it's center of interest and so orbits around the wrong point; only snapping on mouse up. Make sense?

joojaa 2007-07-11 09:01:58 UTC #4

No i cant say it does unless your running animation during the move operation's. Because it as a matter of fact does not cause snap otherwise, but maybe its been fixed in the look at node at some stage (or the move tools who knows) so what version of maya are you running? Or still might be that you have the update tuned to slowest setting.

But if ifd have to tip id say this:

That could be because otherwise the manipulation would possibly lock up completely. (you couldn't key stuff if you hadn't got this behavior the keyframe value would win over in that case), its kind of fundamental to ow maya operates.

Se this is what happens whenever you use tools in maya. The tool creates virtual nodes that connect to the node, these virtual nodes inject values to your attributes that tool needs to affect in this case both aim and point (translate affects translate etc, but camera move tools affect the whole camera). Now to enable you to manipulate stuff with incoming connections, these tools dont look upwards dg history chain. They do this by writing data to the slots marked clean wich means no update needs to be issued (this also terminates the dg loop, so even if it returns later this wont update).

theres a way you can get around this, but its not clean as it subverts entire maya dg principle, you can write a downstream expression that forces the refresh down the line. But this should be avoided so maybe you could jut inject it in only during move of camera.

QUOTE
- When looking through the light and orbiting, the light will often gimbal lock and flip. this makes it very difficult to 'nudge' a light just a little.

thats easily fixed just animate the up axis when you rotate the camera.

user_deleted 2007-07-12 16:27:26 UTC #5

Joojaa--thanks for the tips. I will look into some of that although I really wish Maya had a 'Create Light and Aim' that behaved like 'Create Camera and Aim'...

joojaa 2007-07-13 10:07:10 UTC #6

But you just made one, jut put it in the menus. And then you do.

all you need is to put that script into a mel file of same name ass the proc you maake it into, then add:

menuItem -p MayaWindow|mainCreateMenu|LightsItem -l "Spot Light with Aim" -c "yourPorc()"

to your userSetup.mel, then it will be there whan you next tinme start maya.

This is the entire point of maya, since they cant anticipate all existing needs they let you anticipate all your needs. Which is much easier.

PS: the fact that all other views are off when you move the camera is normal maya behavior it even happens to cameras

PPS: yes theres a 2 bugs in your code you dont group the structure so run:

parent locator1 spotLight1_group;
parent spotLight1 spotLight1_group;

also spotlights cont have center of interest but has instead centerOfIllumination. (you can get around this by placing the spotlight sharing the same trasformas a camera camera shape like in the example that follows:
{
CreateCameraAim;
$cam=ls -sl;
$light=spotLight;
$xfm=listRelatives -p $light;
$camS=listRelatives -shapes -type camera $cam[0];
parent -add -shape $light $cam[0];
select $xfm[0];
delete;
setAttr ($camS[0]+".visibility") 0;
}
or you can jsut cahnge your code.
if you want the above to work exactly like a light does by default you need to connect the light angle to the focal length of the hidden camera trough a expression.)

So your code would be corrected by:

CODE
string $light = spotLight;
$shapes=$light;
if ( "transform" != nodeType $light ) { //this is a stupid test
//dont use nodeType they war of its use in the manual
string $parents[] = listRelatives -parent $light;
$light = $parents[0];
}
string $locatorShapeList[] = spaceLocator -p 0 0 0;
string $locatorShape = $locatorShapeList[0];
string $target = $locatorShape;
string $lookAt = createNode -name ($light+"\_group") "lookAt";

setAttr ".aimVector" -type double3 0 0 -1;

connectAttr ($lookAt+".constraintRotateX") ($light+".rotateX");
connectAttr ($lookAt+".constraintRotateY") ($light+".rotateY");
connectAttr ($lookAt+".constraintRotateZ") ($light+".rotateZ");

connectAttr ($lookAt+".distanceBetween") ($shapes+".centerOfIllumination");

maybe that fixes the problem for you?!?

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