Unprecise description of gradient input for interpolate_gradient

[yzobus]

To use interpolate_gradient each vertex must have a height and a gradient defined. However, it is unclear what input is expected for the gradient, as the function only accepts [f64; 2]. From this, it certainly cannot be a 3d normal vector of each vertex.
It would be helpful to have a more precise description or an example with a non-default value of [0.,0.].

[Stoeoef]

Thank you for bringing this to my attention! I'm a little bit torn on the "unclear what input is expected" part - the gradient refers to the commonly used term gradient (wikipedia) from mathematics, I would expect that to be good enough for the average user of the library. In any case, the least I can do is to include the link to wikipedia in the comment. That will go up with one of my next commits.

Regarding the example I agree - the current version is a little uninspired. I've opened #127 with some ideas to improve the example.

Feel free to reply if you have any other ideas, otherwise I'll close this issue once I have inlcuded the wikipedia link.