Add backend module

src/backend/mod.rs

@@ -0,0 +1,28 @@
+//! This module defines backends for WebAssembly execution.
+//!
+//! Canary is designed to support multiple WebAssembly runtimes for different
+//! purposes. Currently, [wasmtime](https://wasmtime.dev) is the only one
+//! implemented, but in the future, [wasm3](https://github.com/wasm3/wasm3)
+//! will also be provided.
+
+use super::*;
+
+/// A WebAssembly runtime backend.
+pub trait Backend {
+    fn load_module(&self, module: &[u8]) -> Arc<dyn Instance>;
+}
+
+/// An instance of a WebAssembly module.
+///
+/// All self parameters to this trait's functions are immutable, so the
+/// implementation must provide interior mutability. This allows instances
+/// to intelligently optimize the execution of their scripts, for example, by
+/// allowing the execution of multiple ABI calls from multiple threads when
+/// a script supports the WebAssembly multithreading extension.
+pub trait Instance {
+    fn bind_panel(&self, panel: PanelId, msg: Vec<u8>) -> u32;
+    fn update(&self, panel: PanelId, dt: f32);
+    fn draw(&self, panel: PanelId) -> Vec<DrawCommand>;
+    fn on_cursor_event(&self, panel: PanelId, kind: CursorEventKind, at: Vec2);
+    fn on_message(&self, panel: PanelId, msg: Vec<u8>);
+}

src/lib.rs

@@ -7,6 +7,7 @@ use slab::Slab;
 use std::collections::HashMap;
 use std::sync::Arc;
 
+pub mod backend;
 pub mod text;
 
 /// Proportion constant between pixels (at 96dpi) to millimeters (Canary's unit measurement).