* Minimal graphical applications in BQN

Bindings for [[https://github.com/zserge/fenster][Fenster]], providing a set of functions for displaying a
window and setting the color of individual pixels inside.

** Setup

Clone the repository recursively (~git clone --recurse-submodules~)
and run ~make~ to build the shared library. The Makefile should work
on Linux and macOS.

** API

- ~OpenWindow w‿h‿t~ opens a window of width ~w~ and height ~h~, with
  title ~t~. Returns a window handle.
- ~CloseWindow w~ closes a window given its handle ~w~.
- ~F _render w~ runs the function ~F~ at each coordinate of the window
  ~w~ and set the corresponding pixel color. ~F~ should be a function
  returning a color as an RGB triplet in the (0,1) range, and taking a
  list of three elements ~x‿y‿t~, where ~x~ and ~y~ are the pixel
  coordinates and ~t~ is the time.

** Example

See [[./example.bqn][example.bqn]].

#+begin_src bqn
f←•Import "fenster.bqn"

size←500

w←f.OpenWindow size‿size‿"bqn-fenster example"

Rainbow←{𝕊x‿y‿t:
  x‿y↩x‿y÷size
  t↩(100|t)÷100
  h←(x+y)÷2
  f.HSVtoRGB⟨360×h,1,1⟩
}

Rainbow f._render w

•Delay 3

f.CloseWindow w
#+end_src

[[./example.png]]