fix(ios): take the Metal drawable on first draw; threaded WebGL layer changes off main

crates/canvas-2d/src/context/mod.rs

@@ -379,9 +379,6 @@ impl Context {
         self.surface_data.scale
     }
 
-    // Acquiring the next drawable during presentation can block the display-link
-    // callback on tvOS. Keep the previous surface until the next operation needs
-    // to draw, then retain its contents when swapping the backing texture.
     #[inline]
     /// Runs before every draw. Skia uploads a raster image the moment a draw records it (a pattern
     /// fill, say), so another canvas's GL context being current puts the texture in the wrong one.
@@ -397,8 +394,13 @@ impl Context {
         if let Some(ref context) = self.gl_context {
             context.make_current();
         }
-        #[cfg(all(feature = "metal", target_os = "tvos"))]
-        if self.metal_context.as_ref().is_some_and(|c| !c.has_current_drawable()) {
+        // A drawable is taken only when the frame first draws; see `Context::present`.
+        #[cfg(feature = "metal")]
+        if self
+            .metal_context
+            .as_ref()
+            .is_some_and(|c| !c.is_offscreen() && !c.has_current_drawable())
+        {
             Self::acquire_drawable(self);
         }
     }

crates/canvas-2d/src/context/surface_metal.rs

@@ -423,19 +423,17 @@ impl Context {
         }
     }
 
+    /// The next drawable is taken on the next draw (`bind_surface`), not here: holding one
+    /// between frames starves the layer's pool. `replace_backend_texture` keeps the contents.
     pub fn present(context: &mut Context) {
         let _ = MetalContext::new_release_pool();
 
         if let Some(context) = context.metal_context.as_mut() {
             context.present_drawable();
         }
-
-        #[cfg(not(target_os = "tvos"))]
-        Self::acquire_drawable(context);
     }
 
     pub(crate) fn acquire_drawable(context: &mut Context) {
-        #[cfg(target_os = "tvos")]
         let _pool = MetalContext::new_release_pool();
         let mut info: Option<TextureInfo> = None;
         let mut width = 0;

crates/canvas-c/src/offscreen/apple.rs

@@ -96,7 +96,9 @@ fn set_drawable_properties(layer: &ObjRef, retained: bool) {
             forKeys: keys.as_ptr(),
             count: 2usize
         ];
-        let _: () = msg_send![&*layer.0, setDrawableProperties: properties];
+        canvas_core::gpu::gl::change_view_layer(|| {
+            let _: () = msg_send![&*layer.0, setDrawableProperties: properties];
+        });
     });
 }