cat that moves

.envrc

+use flake
\ No newline at end of file

.gitignore

+/target
+.direnv
\ No newline at end of file

Cargo.toml

+[package]
+name = "rapidriter-cat"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+bitvec = "1.0.1"
+
+[build-dependencies]
+image = "0.25.5"
+bitvec = "1.0.1"
+
+[profile.release]
+opt-level = "z"
+lto = true
+strip = "symbols"

Makefile

+text:
+	cargo build --release --target wasm32-unknown-unknown
+	wasm2wat target/wasm32-unknown-unknown/release/rapidriter_cat.wasm > target/rapidriter-cat.wat

build.rs

+use std::{env, fs::File, io::Write, path::Path};
+
+use bitvec::{order::Msb0, vec::BitVec};
+use image::{GenericImageView, ImageReader};
+
+// Example custom build script.
+fn main() {
+    println!("cargo::rerun-if-changed=assets/*");
+    println!("cargo::rerun-if-changed=build.rs");
+
+    let img = ImageReader::open("src/assets/cat.png")
+        .unwrap()
+        .decode()
+        .unwrap();
+
+    assert_eq!(img.width(), 96);
+    assert_eq!(img.height(), 38);
+
+    let mut out: BitVec<u8, Msb0> = BitVec::new();
+
+    for y in 0..img.height() {
+        for x in 0..img.width() {
+            let p = img.get_pixel(x, y);
+            let on = match (p.0[0], p.0[1], p.0[2]) {
+                (0, 0, 0) => true,
+                (255, 255, 255) => false,
+                (r, g, b) => panic!("Invalid pixel at ({x}, {y}): ({r}, {g}, {b})"),
+            };
+
+            out.push(on);
+        }
+    }
+
+    let out_dir = env::var("OUT_DIR").unwrap();
+
+    let mut f = File::create(Path::new(&out_dir).join("cat.bin")).unwrap();
+    f.write_all(&out.as_raw_slice()).unwrap();
+}

flake.lock

+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "ref": "main",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1739866667,
+        "narHash": "sha256-EO1ygNKZlsAC9avfcwHkKGMsmipUk1Uc0TbrEZpkn64=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "73cf49b8ad837ade2de76f87eb53fc85ed5d4680",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils?ref=main";
+  };
+
+  outputs =
+    inputs:
+    inputs.flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = inputs.nixpkgs.legacyPackages.${system};
+      in
+        {
+          devShells.default = pkgs.mkShell {
+            packages = (
+              with pkgs;
+              [
+                gnumake
+                wabt
+              ]
+            );
+          };
+        }
+    );
+}

src/lib.rs

+use bitvec::{order::Msb0, view::BitView};
+
+const WIDTH: usize = 96;
+//const HEIGHT: usize = 38;
+
+#[no_mangle]
+pub extern "C" fn next_frame(frame: u16, ptr: *mut u8) -> u8 {
+    let out = unsafe { std::slice::from_raw_parts_mut(ptr, 456) }.view_bits_mut::<Msb0>();
+
+    if frame > 100 {
+        return 1;
+    }
+
+    let cat = include_bytes!(concat!(env!("OUT_DIR"), "/cat.bin")).view_bits::<Msb0>();
+
+    for x in 0..96 {
+        for y in 0..38 {
+            let out_idx = index(x, y);
+            let in_idx = index((x - frame as usize * 4) % WIDTH, y);
+
+            out.set(out_idx, cat[in_idx]);
+        }
+    }
+
+    0
+}
+
+fn index(x: usize, y: usize) -> usize {
+    x + y * WIDTH
+}