Rust

How small?

Small enough that the number is the reason to pick it:

examples/hello      7,677 bytes wasm   1 import  (env.wc_log)
examples/hello_gl   1,905 bytes wasm  22 imports (env.wc_log + 21 gl.*)

The GL cart is under 2 KB because there is nothing to carry: no interpreter, no garbage collector, no standard library it did not ask for.

Set up

Everything below lives in wasmcart/wasmcart-rust.

rustup target add wasm32-unknown-unknown
cargo add wasmcart

Then in Cargo.toml. The release profile is what keeps carts small, so it is worth copying as-is:

[lib]
crate-type = ["cdylib"]

[profile.release]
opt-level = "z"
lto = true
panic = "abort"
strip = true
codegen-units = 1

A whole cart

Not an excerpt. This is the entire program:

#![no_std]

use wasmcart::*;

wc_cart!(320, 240);

#[no_mangle]
pub extern "C" fn wc_init() {
    wc_log("hello from rust");
}

#[no_mangle]
pub extern "C" fn wc_render() {
    let buf = fb();
    for (i, px) in buf.iter_mut().enumerate() {
        *px = 0xFF00_0000 | (i as u32 & 0xFFFF);
    }
}

wc_cart!(w, h) declares every buffer the ABI needs, the live wc_info_t, wc_get_info, and a panic handler. You write wc_init and wc_render. Notably, a cart author writes no unsafe around a mutable static.

Build and run

cargo build --release --target wasm32-unknown-unknown

npx wasmcart pack --wasm target/wasm32-unknown-unknown/release/my_game.wasm \
  --name my-game --width 320 --height 240 -o my-game.wasc

npx wasmcart my-game.wasc

What you get

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