Finding the reflection point on a curved surface

for a curved mirror surface z = f(x,y), how to find the point of reflection on the surface from a source at (x0,y0,z0)?

is there a function for this?

Thanks

[Sindar]

No, (I'm pretty sure) there isn't a function that does this directly. But, if you can phrase it as a math/code question rather than a physics one, it's likely there is a simple way of doing it