Fenster

Fenster /ˈfɛnstɐ/ -- a German language word for "window".

This library provides the most minimal and highly opinionated way to display a cross-platform 2D canvas. If you remember Borland BGI or drawing things in QBASIC or INT 10h- you know what I mean.

What it does for you

• Single application window of given size with a title.
• Application lifecycle and system events are all handled automatically.
• Minimal 24-bit RGB framebuffer.
• Cross-platform keyboard events (keycodes).
• Cross-platform timers to have a stable FPS rate.
• It's a single header in plain C99 of ~300LOC with no memory allocations.

What it might do for you in the next version

• Mouse events (at least left button click + XY)
• Audio playback (WinMM, CoreAudio, ALSA)
• Bindings for Go, Zig, Rust, Nim, Python...

What it will never do for you

• GUI widgets - use Qt or Gtk or WxWidgets.
• Complex drawing routines or OpenGL - use Sokol or MiniFB or Tigr.
• Low-latency audio - use PortAudio, RtAudio, libsoundio etc.

In other words, you get a single super tiny C file, with a very simple API and it allows you to build graphical apps (simple games, emulators) in a very low-level retrocomputing manner.

Example

Here's how to draw white noise:

#include "fenster.h"
#define W 320
#define H 240
int main() {
  uint32_t buf[W * H];
  struct fenster f = { .title = "hello", .width = W, .height = H, .buf = buf };
  fenster_open(&f);
  while (fenster_loop(&f) == 0) {
    for (int i = 0; i < 320; i++) {
      for (int j = 0; j < 240; j++) {
        fenster_pixel(&f, i, j) = rand();
      }
    }
  }
  fenster_close(&f);
  return 0;
}

Compile it and run:

# Linux
cc main.c -lX11 -o main && ./main
# macOS
cc main.c -framework Cocoa -o main && ./main
# windows
# TODO, but link with -lgdi32

That's it.

API

struct fenster {
  const char *title; /* window title */
  const int width; /* window width */
  const int height; /* window height */
  uint32_t *buf; /* window pixels, 24-bit RGB, row by row, pixel by pixel */
  int keys[256]; /* keys are mostly ASCII, but arrows are 17..20 */
  int mod;       /* mod is 4 bits mask, ctrl=1, shift=2, alt=4, meta=8 */
};

• int fenster_open(struct fenster *f) - opens a new app window.
• int fenster_loop(struct fenster *f) - handles system events and refreshes the canvas. Returns negative values when app window is clsoed.
• void fenster_close(struct fenster *f) - closes the window and exists the graphical app.
• void fenster_sleep(int ms) - pauses for ms milliseconds.
• int64_t fenster_time() - returns current time in milliseconds.

License

Code is distributed under MIT license, feel free to use it in your proprietary projects as well.