How do I constrain object to surface

[david-thomson--2]

I'm making a model and I'm figuring out how add pupils to the model. The eyes are not sperical and they are a single mesh. I'm going for a cartoon kind of look.
I was thinking that I could create somekind of pupil geometry the constrain this to the surface of the eye. I could then move this around by some kind of control?
I was also think that I might be able to do this using textures. I was thinking I could add a pupil texture to the model then move it around using a constraint or something. I'm not even sure what I should be googling to find out more.
Any help would be great.

I have included some links to images of my eyes.

[joojaa]

use pointOnMeshInfo nodes (available for compile in the devkit). Or use the rivet script. Or bind to a follicle.

[raghu-fx]

u can use rivert script for this problem

[alkaloid-xlo]

the rivert plugin its best recommended for the constraining. but u can manually constraint to objects using the constrain options like point constraint, aim constraint etc. in the animation menu and constraint tab. but note that the maintain offset is on so that the current position of the object wont be affect after constraining. hope it helps. its simple.