* Things To Do

** DONE Game loop
   Provide a game loop structure that responds to input events,
   updates the game state, renders the scene. Use a fixed update
   timestep and cap the maximum FPS.

** DONE Input
   Provide hooks to respond to keyboard, mouse, and joystick events.
   Wrap SDL keycode, mouse button, etc. constants in our own
   enumeration.

   - [X] Keyboard
   - [X] Mouse
   - [X] Window (active, resize, quit)
   - [X] Joystick

** DONE Sprites
   Encapsulates an image and all of its transformations: position,
   rotation, scale, color, etc.

   - [X] Use FreeImage
   - [X] Add support for texture regions
   - [X] Add support for animations
   - [X] Use a sprite batch when drawing if one is currently bound

** TODO Sprite batches
   Efficiently render a large number of sprites. Only change OpenGL
   context when necessary. For example, don't change texture when
   rendering several sprites in a row that use the same one.

** DONE Tilesets
   Break an image up into many small pieces. Useful for creating maps.

   - [X] Algorithm to split texture into tiles
   - [X] <tileset> type

** DONE Animations
   Create a data type to represent an animated sequence of textures
   and/or texture regions.

** TODO Tile maps
   - [ ] Create a generic tilemap module
   - [ ] Create a loader for Tiled .tmx map files.

** DONE Scene graph
   A tree structure that is traversed when rendering a game scene.
   The graph is composed of groups and nodes. Transformations are
   accumulated as the tree is walked.

** DONE Scripting
   Provide a way for users to easily script 2D games using coroutines
   and a scheduler.

   - [X] Coroutines
   - [X] Agenda

** DONE Vectors and matrices
   Vectors and matrices are needed constantly for games. Provide an
   easy-to-use module that provides procedures for common
   vector/matrix math operations

   - [X] Vectors
   - [X] Matrices

** DONE Fonts
   - [X] Write wrappers for needed FTGL functions
   - [X] Write font rendering procedures

** DONE Sound
   Provide helpful wrappers around SDL sound procedures?

** TODO A* pathfinding
   A* is a commonly used pathfinding algorithm for games. Pathfinding
   is such a common task that it would be nice to provide users with
   a generic implementation.

** TODO Bounding box collision detection
   Most games need simple bounding box collision detection. Provide an
   efficient implementation that uses quad trees.

   - [X] Rect module
   - [ ] Quadtree module (needs more thought, a purely functional data
     structure would be preferable)

** TODO Particle systems
   Provide a highly configurible particle simulation system.

   - [ ] Investigate ways to make it fast.  Use guile-compost for
     performance reasons.

** TODO Asset Management
   Provide a generic system for loading assets (images, sounds, fonts,
   etc.) and storing them in a cache. Explore using weak keys so that
   assets are removed from the cache when they are no longer
   referenced.

   - [ ] Create asset cache
   - [X] Live asset reloading

** TODO Keymaps
   Provide an Emacs-like way of defining key combinations so that
   multi-button input is easy for users.

   - [ ] Abstract away input methods
     Controls can be bound to keys, mouse, whatever
   - [ ] Basic sequences
     Press A then B
   - [ ] Simultaneous key presses
     Press A and B at the same time
   - [ ] Composing sequences
     Press A then B + C
   - [ ] Timeouts
     Press A then B then C within 15 frames time
   - [ ] Sequences with actions along the way
     Press A to kick, then forward + B to uppercut, within 30 frames
     time.

** TODO GUI widgets
   Provide a set of common graphical widgets such as buttons, scroll
   bars, and sliders.

** DONE REPL
   Provide a REPL that plays nice with the game loop. Easier said than
   done.

   - [X] Modify Guile's REPL to work with the game loop
     - Short-term solution that *mostly* works
   - [X] Write a new REPL that runs in the current thread
     - Use coroutines
     - Read user input from a separate thread so as to not block the
       main thread
     - Will be available in Guile 2.0.10!

** TODO Shaders
   - [ ] Scheme -> GLSL compiler
     Port http://wiki.call-cc.org/eggref/4/glls to guile?

** TODO Upgrade to SDL2
   Write necessary bindings and release [[https://git.dthompson.us/guile-sdl2.git][guile-sdl2]].

** TODO "Nine patches"
    Images that have a resizable central area but fixed width/height
    edges.  See [[https://developer.android.com/guide/topics/graphics/2d-graphics.html#nine-patch][this Android document]] for details.

** TODO Job control for agenda
   Allow for pausing and cancelling jobs.

** TODO Async/threaded signals?
   Not sure how to do this as some things, such as SDL and OpenGL
   calls, *must* be done in the main thread.  Maybe signals should
   just stay synchronous.

** TODO Smooth animation helper
   Remove the temporal aliasing in animation by interpolating between
   current and previous state of animated objects.

** TODO Bitmap font rendering from tileset
   Some fonts aren't available in TTF format, only as a tileset image.
   It would very useful for 2D games to be able to render these.  Even
   better if the font rendering procedures are made polymorphic to
   handle this new type of font.

** TODO Geometry combinators
   A functional interface for composing complex geometry from the
   simple building block of triangles.  A square is 2 triangles, a
   cube is 6 squares, etc.  A triangle has 3 vertices with a
   particular winding.

** TODO 0.1 Release
   A 0.1 release was made under the project's old name, guile-2d.  Now
   that things have changed so drastically and the name has been
   changed, a new 0.1 release will be made.

   - [X] New REPL server
     Use the (system repl coop-server) module in Guile 2.0.11.
   - [ ] Screencast
   - [-] Relatively complete documentation (it's a start)
   - [X] Clean up font module
   - [X] Add GLSL shaders
   - [X] Finish FRP module
   - [X] Make basic webpage with HTML docs
   - [X] Basic rendering (must support sprites and text)