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+# Minimal graphical applications in BQN
+
+Bindings for [Fenster](https://github.com/zserge/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).
+
+```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
+```
+
+![img](./example.png)