DESIGN

# TODO

Diffuse lighting:
* Modify structs to contain normal vectors -- fruit
* Migrate main program loop to Racket -- brain
* Update vboify to convert normal vectors as well
* Check order of vertices in each face in example.plum

## Input/Output
Input:
* Error code

Output (Racket -> C):
* struct Mesh -- when user loaded .plum file for the first time
  e.g. (draw-mesh c-mesh)
* Mesh changeset (delta)

## Sending mesh data from Racket to C

There are two ways:

* Flatten Racket mesh into a giant array and send to C
  + May introduce less bugs
  - Inefficient in converting list to vector and back and forth:
    - Homemade vector-flatten and vector-apply are inefficient
    - vector-append might be expensive (and list append without a doubt)
    - list->pointer conversion function only receives list; mesh is vector
  - Have to send C the whole changeset of VBO array, which is bulky
    (since C is not aware of Mesh data anymore)

* Convert Racket mesh into C struct and flatten it there
  + Expected to be faster
  + More uniform code, since the C struct is the only ring of connection
    between Racket and C
  + Only have to send idiomatic changeset (eg. move 11th vector by delta-vector)
    which is cheap and cool
  - May introduce more bugs
  - Have to fiddle with list lengths