notnull games

WAT

  • Template: cart_wat - press "Use this template" and you have a working game.
  • Docker image: ghcr.io/notnullgames/null0-cart-wat:latest
  • Your code: cart/main.wat, compiled with wat2wasm
  • Bindings: carts/wat/null0.wat (a reference list to copy from)
  • WASI is available, so ordinary file and stdio calls work.
  • See carts made with WAT
  • API docs for WAT

building

You do not install wat2wasm - the docker image has it, and the current null0 bindings, baked in. There is nothing in your project to keep in sync with the engine.

docker run --rm --user $(id -u):$(id -g) \
  -v ./cart:/src -v ./webroot:/out \
  ghcr.io/notnullgames/null0-cart-wat:latest mygame

The template wraps that in npm start, which also serves the result and rebuilds when you save.

WAT notes

  • Raw wasm text - no include mechanism, so copy the imports you need out of null0.wat.
  • A Color is a *pointer to 4 bytes* you write into memory yourself.
  • No malloc, so struct-returning functions do not work on the web host.

a cart, in WAT

This is carts/wat/simple/main.wat in the engine repo - the same file CI builds into the cart below, so it always compiles.

(module
  ;; every language's `simple` cart draws exactly this - see carts/wat/null0.wat
  ;; for the full import list
  (import "null0" "clear" (func $clear (param i32)))
  (import "null0" "draw_circle" (func $draw_circle (param i32 i32 i32 i32)))
  (import "null0" "draw_text" (func $draw_text (param i32 i32 i32 i32 i32)))

  ;; two pages: the data below sits at 65536, which is one page in - with 1
  ;; page the module fails to instantiate ("data segment is out of bounds").
  ;; exported because the host reads Color and string pointers out of it.
  (memory (export "memory") 2)

  (data (i32.const 65536) "\00\79\f1\ff") ;; BLUE = rgba(0, 121, 241, 255)
  (global $blue i32 (i32.const 65536))
  (data (i32.const 65540) "\e6\29\37\ff") ;; RED = rgba(230, 41, 55, 255)
  (global $red i32 (i32.const 65540))
  (data (i32.const 65544) "\ff\ff\ff\ff") ;; WHITE = rgba(255, 255, 255, 255)
  (global $white i32 (i32.const 65544))

  ;; "hello from WAT", null-terminated
  (data (i32.const 65548) "\68\65\6c\6c\6f\20\66\72\6f\6d\20\57\41\54\00")
  (global $text i32 (i32.const 65548))

  (func (export "load")
    (call $clear (global.get $blue))
    (call $draw_circle
      (i32.const 100) (i32.const 100) (i32.const 50)
      (global.get $red))
    (call $draw_text
      (i32.const 0)            ;; FONT_DEFAULT
      (global.get $text)
      (i32.const 170) (i32.const 92)
      (global.get $white)))

  (func (export "update"))
)
carts/wat/simple/main.wat

callbacks

A cart implements the callbacks it cares about. In WAT they look like this:

(func (export "update") ...)

See anatomy of a cart for the full list and what each one is passed.