* 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

High-level API:
- ~F _display width‿height~ creates a window of the given dimensions
  and displays its left operand. ~F~ should be a function returning a
  color as an RGB triplet in the (0,1) range, and taking a list of two
  elements ~x‿y~, where ~x~ and ~y~ are the pixel coordinates.

Low-level 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~ is a function with
  the same arguments as for ~_display~.

** Example

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

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

size←500

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

Rainbow f._display size‿size
#+end_src

[[./example.png]]