Examples and reference for the Rockland Steel House programming series.
Last updated: 23 February 2019
Wade Brainerd
Michael Vance
This is the presentation material that we went over in the advanced track at Steel House.
This is the variation presented at Bowdoin.
We are using the Pico-8 environment in order to get started quickly and get bits up on screen. Both Wade and I have a license which supports spawning for educational purposes such as the Steel House series.
Pico-8 uses a fairly restricted subset of Lua but it's still useful to read up on the language.
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Programming in Lua
Some interesting quirks of the Pico-8 implementation of Lua:
- PICO-8 numbers only go up to 32767.99. If you add 1 to a counter each frame, it will overflow after around 18 minutes!
- Lua arrays are 1-based by default, not 0-based. FOREACH starts at T[1], not T[0].
- cos() and sin() take 0..1 instead of 0..PI * 2, and sin() is inverted.
- sgn(0) returns 1.
- It seems that line number correspondence for Lua errors is off by 3 lines, possibly due to the Pico-8 header lines.
There are some snippets in the tree that demonstrate simple Lua concepts:
- iter.lua - Shows the difference between iterating over keys and values in a table versus a sequence of integers.
- value-reference.lua - Shows some of the differences in behaviors between atomic value types and reference-value types.
A Khan walk through of deriving rotation matrices in two and three dimensions.
These are bits that are particularly advanced/gnarly. The first discuss object-oriented approaches in Lua. Pico-8's Lua implementation supports setmetatable() but not some of the other infrastructure necessary to implement some of those approaches.
Pico-8 uses a 16:16 representation as opposed to the traditional 64-bit float in Lua, which is why the maximum value of a number in Pico-8 is 32767.9, repeating.
There are also some source snippets in the tree that demonstrate some of these advanced concepts.
- vec2d_t.lua, shim.lua - This implements a simple vec2d_t 'class' and shows how to use it, including using the __call method. Ultimately this method is unworkable for Pico-8 as the global 'require' is not supported in the Pico-8 Lua subset.
For those who were interested in a history and explanation of early ray-casting software 3-D engines, I recommend Fabien's book "Game Engine Black Book - Wolfenstein 3-D".
- ast1.p8 - In which we demonstrate some simple line drawing and TTY output, as well as discuss some simple linear algebra.
- ast2.p8 - In which we demonstrate a composite variable (table) and correct a bug.
- ast3.p8 - In which we attempt to build a class-like object.
- ast4.p8 - In which we abandon an attempt to build a class-like object, move to a saner C-like interface, and also start to build an object representation for the game.
- ast5.p8 - In which we implement impulse and world wrapping, and build a proper looking ship.
- ast6.p8 - In which we provide ammunition for our experience, further building out state and related infrastructure.
- ast7.p8 - In which we provide an awesome starfield because the world looks lonely, and fix a bug in our shooty bits.
- ast8.p8 - In which we add asteroid targets and a console.
- ast9.p8 - In which we add melodious sounds.
- ast10.p8 - In which we add a score mechanism, and your score is reset any time the ship intersects with an asteroid.
- Add a thruster effect to the back of the ship.
- Add particle effects and sound when the asteroids are shot.
- Improve the acceleration curve on the ship's thruster.
- Fix the behavior when you shoot at high ship speed.
- Make the starfield scroll relative to the ship speed.
- Draw the asteroids as line segments instead of circles.
- Have the asteroids explode into other asteroids.
- Make the asteroids rotate as they move around.
- Add collision for the ship against the edges of the screen, rather than wrap-around.
- Implement a game over screen and restart mechanism.
- Add a persistent high score mechanism using the cartridge memory built-ins. Bonus points for an initials entry UI.