Make wasm port work again

This cheats somewhat, using the non-robust version of the pipeline for
wasm, and blocking on native.

examples/with_winit/src/main.rs

@@ -188,24 +188,35 @@ async fn run(event_loop: EventLoop<UserEvent>, window: Window, args: Args) {
                 .surface
                 .get_current_texture()
                 .expect("failed to get surface texture");
-            let fut = async {
-                renderer
-                    .render_to_surface_async(
+            #[cfg(not(target_arch = "wasm32"))]
+            {
+                block_on_wgpu(
+                    &device_handle.device,
+                    renderer.render_to_surface_async(
                         &device_handle.device,
                         &device_handle.queue,
                         &scene,
                         &surface_texture,
                         width,
                         height,
-                    )
-                    .await
-                    .expect("failed to render to surface");
-                surface_texture.present();
-            };
-            #[cfg(not(target_arch = "wasm32"))]
-            block_on_wgpu(&device_handle.device, fut);
+                    ),
+                )
+                .expect("failed to render to surface");
+            }
+            // Note: in the wasm case, we're currently not running the robust
+            // pipeline, as it requires more async wiring for the readback.
             #[cfg(target_arch = "wasm32")]
-            wasm_bindgen_futures::spawn_local(fut);
+            renderer
+                .render_to_surface(
+                    &device_handle.device,
+                    &device_handle.queue,
+                    &scene,
+                    &surface_texture,
+                    width,
+                    height,
+                )
+                .expect("failed to render to surface");
+            surface_texture.present();
             device_handle.device.poll(wgpu::Maintain::Poll);
         }
         Event::UserEvent(event) => match event {

src/lib.rs

@@ -182,7 +182,7 @@ impl Renderer {
     ) -> Result<()> {
         let mut render = Render::new();
         let encoding = scene.data();
-        let recording = render.render_encoding_coarse(encoding, &self.shaders, width, height);
+        let recording = render.render_encoding_coarse(encoding, &self.shaders, width, height, true);
         let target = render.out_image();
         let bump_buf = render.bump_buf();
         self.engine.run_recording(device, queue, &recording, &[])?;

src/render.rs

@@ -196,9 +196,7 @@ pub fn render_encoding_full(
     height: u32,
 ) -> (Recording, ResourceProxy) {
     let mut render = Render::new();
-    // TODO: leaks the download of the bump buf; a good way to fix would be to conditionalize
-    // that download.
-    let mut recording = render.render_encoding_coarse(encoding, shaders, width, height);
+    let mut recording = render.render_encoding_coarse(encoding, shaders, width, height, false);
     let out_image = render.out_image();
     render.record_fine(shaders, &mut recording);
     (recording, out_image.into())
@@ -223,12 +221,16 @@ impl Render {
     }
 
     /// Prepare a recording for the coarse rasterization phase.
+    ///
+    /// The `robust` parameter controls whether we're preparing for readback
+    /// of the atomic bump buffer, for robust dynamic memory.
     pub fn render_encoding_coarse(
         &mut self,
         encoding: &Encoding,
         shaders: &FullShaders,
         width: u32,
         height: u32,
+        robust: bool,
     ) -> Recording {
         use crate::encoding::{resource::ResourceCache, PackedEncoding};
         let mut recording = Recording::default();
@@ -526,7 +528,9 @@ impl Render {
             info_bin_data_buf,
             out_image,
         });
-        recording.download(*bump_buf.as_buf().unwrap());
+        if robust {
+            recording.download(*bump_buf.as_buf().unwrap());
+        }
         recording.free_resource(bump_buf);
         recording
     }