chicken-sdl2 0.2.0 Released

Screenshot of a graphics demo showing waves, the moon, stars, and constellations.
Screenshot of “The Sea and the Stars”, a new demo program using chicken-sdl2 0.2.0.
Today I released version 0.2.0 of chicken-sdl2 (aka the sdl2 egg).

chicken-sdl2 provides CHICKEN Scheme bindings to version 2 of the Simple DirectMedia Layer (SDL) game development library.

Highlights of this release include:

  • Support for 2D accelerated rendering (renderer and texture)
  • Support for hints (configuration variables)
  • Support for most SDL 2.0.4 features
  • Efficient color, point, and rect operations
  • Performance improvements
  • Improved integer type checking
  • Miscellaneous other changes

For more details, please see the CHANGELOG.

Many thanks to Kooda Loutre and Kristian Lein-Mathisen for submitting suggestions which have been implemented in this release. :)

Lisp Game Jam Post-mortem

I recently participated in the 2016 Lisp Game Jam, an event where participants had 7 days (later extended to 10 days) to create a computer game using a dialect of Lisp, a family of programming languages. This is a “post-mortem” of that experience, in which I discuss what went well, what could have gone better, what I learned, and so on. Continue reading Lisp Game Jam Post-mortem

Lisp Game Jam Log #4

Screenshot showing a game level with two characters, a coin, and a gem.Today I started on the physics engine for my game. I have implemented the entity record type, which represents dynamic objects like players and items, and the body record type, which represents the physical attributes of an entity, such as its position, velocity, acceleration, dimensions, and mass.

CHICKEN Scheme has several object-oriented programming libraries that support inheritance (I even created my own for fun a few years ago). But so far, I have just been using basic Scheme record types (structures with named slots), and using composition instead of inheritance.

In other words, instead of having the entity type inherit position, velocity, etc. attributes from the body type, an entity has a slot which holds a body. And instead of having a player type and a coin type and a gem type which inherit from entity, an entity has slots to hold other objects which define its appearance and behavior. I’m not opposed to using inheritance when the need arises, but so far while making this game I have not needed it.

Today I also wrote a simple physics update function (apply the acceleration to the velocity, then the velocity to the position), and I now have moving player characters on the screen. There is no collision or user input yet, but by setting the initial attributes of the characters, I can make them fly through the air in a parabola, then fall down off the bottom of the screen. I also added a coin and a gem entity to the scene, just for kicks.

I added user-customizable scaling for the window, since the graphics are a bit small (each tile is 21-by-21 pixels). I’ve shrunk the screenshot in this post so it wouldn’t be too wide, but you can click it to see the full version. The default scale is 200%, but users can edit the settings.scm file to change that if you want. In the future, that file will have other settings like the keyboard/joystick bindings.

The settings file, like the level file, is just a collection of s-expressions. I’m using CHICKEN Scheme’s built-in read-file procedure, which reads (but does not evaluate) all the s-expressions in a file and returns them as a list. This is probably not super secure, since users might be able to exploit the reader in some way to inject code, but it sure is convenient. Besides, security is not a high priority in the heat of a game jam.

My next step is to add detection and resolution of collisions. If this were a shorter game jam, or if I had more complex scenes, I would definitely just use a pre-built physics engine like Chipmunk. But, I think I have enough time to implement a good enough physics engine to handle a simple platformer game like this.

P.S. The in-progress source code is available.

P.P.S. The sprites are from Kenney Game Assets. I got them from donating about a year ago, and they are licensed CC0 public domain. An older version of the same sprites is available with no payment required.

Lisp Game Jam Log #1

The January 2016 Lisp Game Jam officially started earlier tonight. I haven’t participated in a game jam for several years, and I’m excited. Game jams are exciting (and stressful) in general, but I’m also excited because this is my first jam using a Lisp dialect, plus it is an opportunity to use the CHICKEN Scheme bindings to SDL2 and related libraries, which I have been working on for the past several months. (I’m also excited because at least two other people are planning on using my bindings for the jam, which is a nice feeling.)

This game jam does not have a prescribed theme, so I’m free to make any game. I’ve been pondering for weeks about what kind of game I might make for the jam. My goal is to produce another example game for the bindings, so I want the result to be clearly organized, well documented, and to demonstrate the capabilities of the bindings. In particular, I want to try to push the boundaries of performance. My previous game library project, Rubygame, struggled with raw performance, partly because of the performance limitations of Ruby in those days, and partly because I didn’t put much effort into optimization. So, I’m keen to see what I can achieve with CHICKEN Scheme and these bindings.

Thinking about what type of game I’d like to make for the jam, I had two main ideas: a scrolling space shooter à la Tyrian, or a platformer à la Mario Bros. I also briefly considered a Harvest Moon-like RPG, but decided I wouldn’t be able to make it fun in 7 days, and the laid-back gameplay style wouldn’t push any performance boundaries.

Between the space shooter and the platformer, the space shooter would be a more interesting example, because I could try to achieve solid performance while having hundreds of bullets and ships on screen at the same time, and it could use the function bindings I recently added for 2D accelerated rendering. But, those bindings aren’t actually released yet (they are scheduled for version 0.2), so it wouldn’t be as easy for people to install the bindings and play the game. So, I am going to make the platformer game for this jam, and then make the space shooter at some later date.

This game jam allows us to use preexisting free assets (images, sound, music), so to make things easy for myself I am going to use a lot of assets from the Kenney Game Assets pack. (You have to donate money to get the assets from the official store, but they are licensed CC0 public domain, so no doubt they are available somewhere for free.)

In terms of gameplay, I’m thinking the game will be a rowdy local multiplayer game, where players compete to collect the most treasure, like the old Super Mario Bros. Battle Mode. At the most basic level, it could just be treasure periodically appearing at random places on the level, and the players scrambling to reach it first, with no real interaction between players. If I have time, I could add various ways for the players to interact and interfere with each other: bouncing and bumping into each other, triggering traps, throwing items, etc.

This game design is simple and flexible enough that I’m confident I’ll be able to complete something fun during the game, especially since we have 7 days. I will probably try to include 2 or 3 built-in levels, and have a simple text-based file format so that people could create their own levels.

chicken-sdl2-ttf 0.1 Released

Screenshot of the chicken-sdl2-ttf demo program, displaying the text "Hello, World!" three times. Last week I released version 0.1 of chicken-sdl2-ttf (aka the sdl2-ttf egg). This provides bindings to SDL_ttf 2, the font rendering library for SDL. This library is compatible with chicken-sdl2, which I released a couple weeks ago.

SDL_ttf is thankfully a fairly small library, so I was able to create and document complete bindings to it in less than a week, in advance of the January 2016 Lisp Game Jam, which has just started a half hour ago.

My plans now are:

  1. Create a game for the game jam!
  2. Release chicken-sdl2 0.2 (the main new feature is 2D accelerated rendering).
  3. Create bindings for SDL_mixer, and possibly SDL_gfx.

chicken-sdl2 and chicken-sdl2-image 0.1 Released

Today I released two new library bindings to make it easier to develop games with the CHICKEN Scheme programming language:

CHICKEN Scheme has excellent FFI support, so it was previously possible to use SDL2 from CHICKEN Scheme — possible, but not convenient or straightforward. I have made an effort to create programmer-friendly, convenient, thorough, and well-documented bindings. These bindings take care of the annoying low-level C stuff for you, so you can focus on making your game.

Although the version numbers for these libraries are only 0.1, they are ready to start using now. Some features have not been implemented yet, but it is already possible to create many types of games, even 3D games using OpenGL (when combined with the gl-utils or opengl egg, for example). Several demos and example programs are available to help you get started. Large backwards-incompatible changes are unlikely, but there may be small tweaks and fixes to the API if problems are discovered. There may be some bugs, but they will be fixed promptly if you report them to the issue tracker.

I also intend to eventually create bindings for other libraries, such as SDL2_ttf (for text rendering), SDL2_mixer (for sound effects and music), and SDL2_gfx (for shape drawing and image transformation).

In related news, there is a 7-day Lisp Game Jam coming up the first week of January. I will be creating a new example game using these bindings, and hanging out in the IRC channel (my handle is “jacius”) to answer questions about the bindings, CHICKEN Scheme, and SDL in general.

Cloje types vs host types, revisited

While preparing the Cloje 0.2 release last week, I came across something I had written, part of the goals for Cloje:

Importing all of Cloje will allow you to write code in a language very similar to Clojure. Or if you prefer, you will be able to pick and choose which pieces of Cloje to import, so that you are still mostly writing code in Scheme/Lisp, but with some added features from Clojure.

I had written that over a month ago, long before I had explored host interop issues. Reading it again during the release preparations made me wonder if I had neglected this use case when considering the host interop API design.

My consideration of host interop was from the angle of someone who was writing in Cloje, and wanted to interact with certain host language features or libraries. I hadn’t really considered someone who was writing in the host language, and wanted to integrate certain Cloje features or libraries. It made me wonder whether it was accurate to say that users would be able to “mostly write code in Scheme/Lisp”, considering that much of Cloje will probably depend on a bunch of new types.

This got me thinking on a more fundamental level about Cloje’s stance regarding host types. Should it be possible (and acceptable/idiomatic) for Cloje users to decide to write Cloje programs that primarily (or exclusively) use host types? Or are Cloje users expected to primarily use Cloje types, and only use host types for host interop?

Note: When I talk about “Cloje types” and “host types” in this post, I am mostly thinking of lists, vectors, hash maps/tables, and strings. Those are the types where Cloje and the host language would have “colliding” types (analogous types with different implementations), and thus the source of possible trouble. Certain other types (such as symbols, numbers, and functions) are the same type in Cloje as on the host, so no conversion (implicit or explicit) would be needed.

To help me organize my thoughts and guide my decision, I have sketched out a few scenarios for different stances Cloje might take regarding host types, and explored some of the implications of each scenario. Continue reading Cloje types vs host types, revisited

Cloje 0.2.0 Released

Cloje icon Yesterday I tagged version 0.2 of Cloje. If you want to play around with it, you can clone the repository. Installation and usage instructions are available in the README.

In terms of features, the biggest changes in Cloje 0.2.0 are the addition of hash sets (an unordered collection of distinct elements), and several set operations based on the clojure.set standard library. Please read the release notes for the full list of changes in Cloje 0.2.0.

Also noteworthy is that the goal of Cloje has changed since 0.1. For reasons described in the Cloje 0.1 Post-Mortem, Cloje will no longer attempt to faithfully emulate Clojure. Instead, the new goal is to bring the best aspects of Clojure to Scheme/Lisp. The first effects of this new direction can be seen in the new set operations, whose behavior is more predictable and consistent than clojure.set when given non-set collections. The old goal would have required me to laboriously recreate Clojure’s quirks and bugs, rather than address and fix them.

Tentative plans for 0.3 are to create placeholder types (vectors, maps, etc.) and an API to convert between Cloje types and host types. This will set the stage for adding Clojure-style immutable persistent data structures in the future. The placeholder types will be immutable, but not (yet) have the structural sharing of Clojure’s types.

Besides writing code, I will also be dedicating a significant portion of my project time to establishing policies, project documentation (how to start contributing, etc.), and outreach to help get more people involved in the project, especially people from underrepresented groups.

Implementing Metadata in Cloje

This week I’ve been doing planning for Cloje, and trying to figure out how I might approach implementing certain Clojure features. Even if I’m not going to write the code for several weeks, I want to avoid painting myself into a corner.

One such feature is support for metadata. I see three potential approaches one might take when implementing metadata:

  • Wrap the object with a metadata container
  • Inject metadata into the object
  • Store the metadata separately from the object

Each of these solutions is pretty hairy, and there are significant trade-offs involved. So, I wrote this blog post to explore these approaches and hopefully help me decide which to use. Continue reading Implementing Metadata in Cloje