Simplify Iris app initialization and task updates

readme.md

@@ -25,31 +25,48 @@ application-id = "com.example.myapp"
 label = "My app"
 ```
 
-`#[iris::app_init]` marks the factory called when Android creates the Iris
+`#[iris::app_init]` marks the initializer called when Android creates the Iris
 view. The attribute supplies its own Android target gate and generates the JNI
-loader glue. The returned state chooses its resources through
-`AndroidAppState::Resources`; `StdRsc` is the standard bundle, not a
-requirement.
+loader glue. An application with no state beyond the UI state receives
+`AndroidUiState` directly by mutable reference:
 
 ```rust
 use iris::prelude::*;
 
-#[derive(AndroidUiState)]
-struct State {
-    ui_state: AndroidUiState,
-}
-
-impl AndroidAppState for State {
-    type Resources = StdRsc<Self>;
-}
-
 #[iris::app_init]
-fn create(mut ui_state: AndroidUiState, rsc: &mut StdRsc<State>) -> State {
-    rect(PaintId::RED).set_root(rsc, &mut ui_state);
-    State { ui_state }
+fn create(
+    ui_state: &mut AndroidUiState,
+    rsc: &mut StdRsc<AndroidUiState>,
+) {
+    rect(PaintId::RED).set_root(rsc, ui_state);
 }
 ```
 
+Desktop has the corresponding initializer form:
+
+```rust
+DesktopApp::<DesktopUiState>::run_with(|ui_state, rsc| {
+    rect(PaintId::RED).set_root(rsc, ui_state);
+});
+```
+
+Background work updates either host through the same task context. An update
+wakes the UI thread; Iris schedules a frame automatically if the closure made
+the retained widget tree dirty:
+
+```rust
+rsc.spawn_task(async move |mut ctx| {
+    let text = load_text().await;
+    ctx.update(move |_, rsc| label.edit(rsc).set(&text));
+});
+```
+
+Applications do not need a winit event proxy or an explicit redraw request.
+
+Applications with additional fields use their own state type. Its
+`AndroidAppState::Resources` associated type can also replace `StdRsc` with a
+custom resource bundle.
+
 Install the Cargo subcommand from a checkout, then invoke it from the
 application's directory: