Add hot reloading of shaders to the winit example (#252)

Cargo.lock

@@ -2452,6 +2452,16 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "notify-debouncer-mini"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e23e9fa24f094b143c1eb61f90ac6457de87be6987bc70746e0179f7dbc9007b"
+dependencies = [
+ "crossbeam-channel",
+ "notify",
+]
+
 [[package]]
 name = "nu-ansi-term"
 version = "0.46.0"
@@ -4186,6 +4196,7 @@ dependencies = [
  "clap",
  "console_error_panic_hook",
  "console_log",
+ "notify-debouncer-mini",
  "pollster",
  "roxmltree",
  "vello",

Cargo.toml

@@ -29,4 +29,5 @@ moscato = { git = "https://github.com/dfrg/pinot" }
 peniko = { git = "https://github.com/linebender/peniko" }
 
 [features]
+hot_reload = []
 buffer_labels = []

examples/with_winit/Cargo.toml

@@ -16,6 +16,10 @@ pollster = "0.2.5"
 roxmltree = "0.13"
 clap = { version = "4.1.0", features = ["derive"] }
 
+[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
+vello = { path = "../../", features = ["hot_reload"] }
+notify-debouncer-mini = "0.2.1"
+
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 console_error_panic_hook = "0.1.7"
 console_log = "0.2"

examples/with_winit/src/hot_reload.rs

@@ -0,0 +1,28 @@
+use std::{path::Path, time::Duration};
+
+use notify_debouncer_mini::{new_debouncer, notify::*, DebounceEventResult};
+
+pub(crate) fn hot_reload(mut f: impl FnMut() -> Option<()> + Send + 'static) -> impl Sized {
+    let mut debouncer = new_debouncer(
+        Duration::from_millis(500),
+        None,
+        move |res: DebounceEventResult| match res {
+            Ok(_) => f().unwrap(),
+            Err(errors) => errors.iter().for_each(|e| println!("Error {:?}", e)),
+        },
+    )
+    .unwrap();
+
+    debouncer
+        .watcher()
+        .watch(
+            dbg!(&Path::new(env!("CARGO_MANIFEST_DIR"))
+                .join("../../shader")
+                .canonicalize()
+                .unwrap()),
+            // We currently don't support hot reloading the imports, so don't recurse into there
+            RecursiveMode::NonRecursive,
+        )
+        .expect("Could watch shaders directory");
+    debouncer
+}

examples/with_winit/src/main.rs

@@ -18,7 +18,7 @@ mod pico_svg;
 mod simple_text;
 mod test_scene;
 
-use std::{borrow::Cow, path::PathBuf};
+use std::{borrow::Cow, path::PathBuf, time::Instant};
 
 use clap::Parser;
 use vello::{
@@ -26,7 +26,13 @@ use vello::{
     util::RenderContext,
     Renderer, Scene, SceneBuilder,
 };
-use winit::{event_loop::EventLoop, window::Window};
+use winit::{
+    event_loop::{EventLoop, EventLoopBuilder},
+    window::Window,
+};
+
+#[cfg(not(target_arch = "wasm32"))]
+mod hot_reload;
 
 #[derive(Parser, Debug)]
 #[command(about, long_about = None)]
@@ -46,7 +52,7 @@ struct Args {
 
 const TIGER: &'static str = include_str!("../../assets/Ghostscript_Tiger.svg");
 
-async fn run(event_loop: EventLoop<()>, window: Window, args: Args) {
+async fn run(event_loop: EventLoop<UserEvent>, window: Window, args: Args) {
     use winit::{event::*, event_loop::ControlFlow};
     let mut render_cx = RenderContext::new().unwrap();
     let size = window.inner_size();
@@ -194,16 +200,40 @@ async fn run(event_loop: EventLoop<()>, window: Window, args: Args) {
             surface_texture.present();
             device_handle.device.poll(wgpu::Maintain::Wait);
         }
+        Event::UserEvent(event) => match event {
+            #[cfg(not(target_arch = "wasm32"))]
+            UserEvent::HotReload => {
+                let device_handle = &render_cx.devices[surface.dev_id];
+                eprintln!("==============\nReloading shaders");
+                let start = Instant::now();
+                let result = renderer.reload_shaders(&device_handle.device);
+                // We know that the only async here is actually sync, so we just block
+                match pollster::block_on(result) {
+                    Ok(_) => eprintln!("Reloading took {:?}", start.elapsed()),
+                    Err(e) => eprintln!("Failed to reload shaders because of {e}"),
+                }
+            }
+        },
         _ => {}
     });
 }
 
+enum UserEvent {
+    #[cfg(not(target_arch = "wasm32"))]
+    HotReload,
+}
+
 fn main() {
     let args = Args::parse();
     #[cfg(not(target_arch = "wasm32"))]
     {
         use winit::{dpi::LogicalSize, window::WindowBuilder};
-        let event_loop = EventLoop::new();
+        let event_loop = EventLoopBuilder::<UserEvent>::with_user_event().build();
+
+        let proxy = event_loop.create_proxy();
+        let _keep =
+            hot_reload::hot_reload(move || proxy.send_event(UserEvent::HotReload).ok().map(drop));
+
         let window = WindowBuilder::new()
             .with_inner_size(LogicalSize::new(1044, 800))
             .with_resizable(true)
@@ -214,7 +244,7 @@ fn main() {
     }
     #[cfg(target_arch = "wasm32")]
     {
-        let event_loop = EventLoop::new();
+        let event_loop = EventLoopBuilder::<UserEvent>::with_user_event().build();
         let window = winit::window::Window::new(&event_loop).unwrap();
 
         std::panic::set_hook(Box::new(console_error_panic_hook::hook));

src/lib.rs

@@ -149,6 +149,21 @@ impl Renderer {
         self.target = Some(target);
         Ok(())
     }
+
+    /// Reload the shaders. This should only be used during `vello` development
+    #[cfg(feature = "hot_reload")]
+    pub async fn reload_shaders(&mut self, device: &Device) -> Result<()> {
+        device.push_error_scope(wgpu::ErrorFilter::Validation);
+        let mut engine = Engine::new();
+        let shaders = shaders::full_shaders(device, &mut engine)?;
+        let error = device.pop_error_scope().await;
+        if let Some(error) = error {
+            return Err(error.into());
+        }
+        self.engine = engine;
+        self.shaders = shaders;
+        Ok(())
+    }
 }
 
 struct TargetTexture {

src/shaders.rs

@@ -31,9 +31,29 @@ pub const PATH_DRAWOBJ_WG: u32 = 256;
 pub const CLIP_REDUCE_WG: u32 = 256;
 
 macro_rules! shader {
-    ($name:expr) => {
-        include_str!(concat!("../shader/", $name, ".wgsl"))
-    };
+    ($name:expr) => {&{
+        let shader = include_str!(concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/shader/",
+            $name,
+            ".wgsl"
+        ));
+        #[cfg(feature = "hot_reload")]
+        let shader = std::fs::read_to_string(concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/shader/",
+            $name,
+            ".wgsl"
+        ))
+        .unwrap_or_else(|e| {
+            eprintln!(
+                "Failed to read shader {name}, error falling back to version at compilation time. Error: {e:?}",
+                name = $name
+            );
+            shader.to_string()
+        });
+        shader
+    }};
 }
 
 pub struct Shaders {