View Full Version : Modifying the position of a parented light

Tom Wood
05-16-2008, 03:38 PM
Hi All,

I have a character with two eyes and two lights that are exclusively for the purpose of creating the highlite gleam in each eye. The lites are positioned off to one side of the face at about 30 degrees so the highlite is in the iris, and each lite excludes everything else in the scene except the eye it is targeted on.

The lights are parented to the characters head, so that when it turns its head the lights move with it. I've worked out an angle of offset for the lights, plus the maximum range of side to side movement the character's head can make, and keep the highlite within the iris of the eye. If the character turns its head too far the highlite falls outside the iris and just doesn't look right. Adjusting to make it work more in one rotational direction makes it work worse in the other direction.

It seems to me that there might be a modifier that could adjust the angular position of the lights relative to the head, depending on the rotation of the head so that I could keep the highlite in the iris at all times. Which modifier should I be looking at for something like this?


05-16-2008, 06:18 PM
Here's a "thinking outside the box" suggestion: Fake it. Make an image map (or sequence) for the entire eyeball and just paint the highlights in where you want them.

Failing that, it's hard to get a sense of what you need from your description. Can you post some kind of screen cap so we can see what's going on?

Tom Wood
05-16-2008, 07:05 PM
This setup:


produces this image:


If I turn the heads any more in either direction, the highlite moves out of the iris. So I'd like to modify the position of the lights creating the highlite as the rotation of the head changes.

05-16-2008, 07:13 PM
Why not use a distant light(s) to only affect specularity? I would think that with spots you've got more "angular" issues, especially when they're in close proximity to objects, as in your setup.

05-17-2008, 07:31 AM
Well I am no physics expert or mathematician, but my caveman-level experiments have shown me that there is some kind of curve at play here and it has to do with the distance of the light as well as the angle and distance from the object to the camera. There is a drop off on that curve somewhere at more extreme angles. I'd show you my cave sketch but my fire is burning low.

The solution however is to set those fire-emitting boxes - you call lights - real close to the eyes (about an inch or so away) until you find a distance that allows the reflection to remain in a relatively centralized location to your liking throughout that animation. :lwicon:

Tom Wood
05-17-2008, 08:07 AM
Surreal -

That was my first instinct as well, but it just didn't work out as well. I moved them WAY back and made them distant lights, and now I have a larger range of rotational movement that keeps them in the iris. Not to the extreme rotations, but good enough.

Thanks All!

05-17-2008, 08:09 AM
It worked perfect for me and I tested it at extreme angles. You should try again. Just put the light closer.

05-17-2008, 08:21 AM
Ha ha! Sorry. Reading that I sounded a little short. :)

Not sure why it did not work for you but here's what I got. I found that that curve happens abruptly, so that you could move it a smigeon and be good to go.

Tom Wood
05-17-2008, 10:59 AM
Yep, I see what you mean. I think I was trying to do both sets of eyes with one set of lights before. (I'm now at 10 lights and only 8 show up in OpenGL, so I was trying to work under that limit.)


05-17-2008, 12:04 PM
Cool and good luck with it. :)