@node Introduction
@chapter Introduction

Sly is a 2D game development framework for GNU Guile. Guile-2D
aims to be simple for beginners to learn and to provide users with all
of the necessary tools for making 2D computer games, such as sprites,
tilesets, audio, scripting, and collision detection.

This manual is a work in progress. You will find that it is lacking in
many areas. If Sly interests you, please consider helping to
improve the documentation.

@menu
* Purpose::
* The Game Loop::
@end menu

@node Purpose
@section Purpose

There are many existing game libraries and engines already, so why
make another one? Well, I, the author, believe that GNU Guile is a
fantastic Scheme implementation with a great purpose: to bring
practical user freedom to the GNU system via Emacs-like
extensibility. There are many libraries available to make games with
languages such as Python, Java, and Lua, but there isn't much out
there for Scheme. Sly aims to change that.

I originally set out on the journey to write a game in C with a Scheme
scripting layer. A year later, I've decided that it would be best to
create an generic game framework in order to give back to the Guile
community and help promote Guile to game developers.

Sly draws much inspiration from existing game libraries for
other, more popular programming languages. Pygame, pyglet, and love2d
are very beginner friendly, and Sly hopes to translate their good
ideas into the Scheme world.

@node The Game Loop
@section The Game Loop

The game loop is so fundamental that it has to be discussed
immediately, so as to avoid any confusion about how it
operates. Sly's game loop operates on a fixed-timestep of 1/60th
of a second. Time is measured in frames rather than in seconds to
avoid the pitfalls of a variable time-based approach. Though the
update rate is fixed, the frame-rate is not. Sly will render at
as high of a framerate as it can. Keyboard and mouse input is polled
during every update and events are emitted to the relevant callbacks.