Live Asset Reloading with guile-2d

May 04, 2014

Guile-2d provides a dynamic environment in which a developer can build a game incrementally as it runs via the Guile REPL. It’s nice to be able to hot-swap code and have the running game reflect the changes made, but what about the game data files? If an image file or other game asset is modified, it would be nice if the game engine took notice and reloaded it automatically. This is what guile-2d’s live asset reloading feature does.

The new (2d live-reload) module provides the live-reload procedure. live-reload takes a procedure like load-texture and returns a new procedure that adds the live reload magic. The new procedure returns assets wrapped in a signal, a time-varying value. A coroutine is started that periodically checks if the asset file has been modified, and if so, reloads the asset and propagates it via the signal. Game objects that depend on the asset will be regenerated immediately.

Here’s some example code:

(define load-texture/live
  (live-reload load-texture))

(define-signal texture
  (load-texture/live "images/p1_front.png"))

(define-signal sprite
   (lambda (texture)
     (make-sprite texture
                  #:position (vector2 320 240)))

load-texture/live loads textures and reloads them when they change on disk. Every time the texture is reloaded, the sprite is regenerated using the new texture.

Here’s a screencast to see live reloading in action:

Guile-2d is ever-so-slowly approaching a 0.2 release. Stay tuned!