add state scope function

hui-derive/src/lib.rs

@@ -6,8 +6,16 @@ use syn::{parse_macro_input, DeriveInput};
 
 /// Implements `Signal` trait for the given type
 #[proc_macro_derive(Signal)]
-pub fn signal(input: TokenStream) -> TokenStream {
+pub fn derive_signal(input: TokenStream) -> TokenStream {
   let input = parse_macro_input!(input as DeriveInput);
   let name = input.ident;
   quote!(impl ::hui::signal::Signal for #name {}).into()
 }
+
+/// Implements `State` trait for the given type
+#[proc_macro_derive(State)]
+pub fn derive_state(input: TokenStream) -> TokenStream {
+  let input = parse_macro_input!(input as DeriveInput);
+  let name = input.ident;
+  quote!(impl ::hui::state::State for #name {}).into()
+}

hui/Cargo.toml

@@ -28,6 +28,7 @@ derive_setters = "0.1"
 derive_more = "0.99"
 tinyset = "0.4"
 image = { version = "0.25", default-features = false, optional = true }
+rustc-hash = "1.1"
 
 [features]
 default = ["el_all", "image", "builtin_font", "pixel_perfect_text", "derive"]

hui/src/instance.rs

@@ -18,9 +18,7 @@ use crate::{
 /// In most cases, you should only have one instance of this struct, but multiple instances are allowed\
 /// (Please note that it's possible to render multiple UI "roots" using a single instance)
 pub struct UiInstance {
-  //mouse_position: Vec2,
   stateful_state: StateRepo,
-  //event_queue: VecDeque<UiEvent>,
   prev_draw_commands: UiDrawCommandList,
   draw_commands: UiDrawCommandList,
   draw_call: UiDrawCall,
@@ -30,7 +28,7 @@ pub struct UiInstance {
   events: EventQueue,
   input: UiInputState,
   signal: SignalStore,
-  //True if in the middle of a laying out a frame
+  /// True if in the middle of a laying out a frame
   state: bool,
 }
 
@@ -41,7 +39,7 @@ impl UiInstance {
   pub fn new() -> Self {
     UiInstance {
       //mouse_position: Vec2::ZERO,
-      stateful_state: StateRepo::default(),
+      stateful_state: StateRepo::new(),
       //event_queue: VecDeque::new(),
       // root_elements: Vec::new(),
       prev_draw_commands: UiDrawCommandList::default(),

hui/src/state.rs

@@ -2,12 +2,141 @@
 
 use hashbrown::{HashMap, HashSet};
 use nohash_hasher::BuildNoHashHasher;
-use std::any::Any;
+use std::{any::Any, hash::{Hash, Hasher}};
+use rustc_hash::FxHasher;
 
 //TODO impl StateRepo functions and automatic cleanup of inactive ids
 
+#[cfg(feature = "derive")]
+pub use hui_derive::State;
+
+/// Marker trait for state objects
+pub trait State: Any {}
+
+/// Integer type used to identify a state object
+type StateId = u64;
+
+fn hash_local(x: impl Hash, g: &[StateId]) -> StateId {
+  let mut hasher = FxHasher::default();
+  0xdeadbeefu64.hash(&mut hasher);
+  for x in g {
+    x.hash(&mut hasher);
+  }
+  x.hash(&mut hasher);
+  hasher.finish()
+}
+
+fn hash_global(x: impl Hash) -> StateId {
+  let mut hasher = FxHasher::default();
+  0xcafebabeu64.hash(&mut hasher);
+  x.hash(&mut hasher);
+  hasher.finish()
+}
+
 #[derive(Default)]
 pub struct StateRepo {
-  state: HashMap<u64, Box<dyn Any>, BuildNoHashHasher<u64>>,
-  active_ids: HashSet<u64, BuildNoHashHasher<u64>>
+  /// Stack of ids used to identify state objects
+  id_stack: Vec<StateId>,
+
+  /// Implementation detail: used to prevent needlessly reallocating the id stack if the `global`` function is used
+  standby: Vec<StateId>,
+
+  /// Actual state objects
+  state: HashMap<StateId, Box<dyn Any>, BuildNoHashHasher<StateId>>,
+
+  /// IDs that were accessed during the current frame, everything else is considered inactive and can be cleaned up
+  active_ids: HashSet<StateId, BuildNoHashHasher<StateId>>
+}
+
+impl StateRepo {
+  /// Push an id to the stack
+  pub fn push(&mut self, id: impl Hash) {
+    self.id_stack.push(hash_global(id));
+  }
+
+  /// Pop the last id from the stack
+  ///
+  /// ## Panics:
+  /// Panics if the stack is empty
+  pub fn pop(&mut self) {
+    self.id_stack.pop().expect("stack is empty");
+  }
+
+  /// Create a new [`StateRepo`]
+  pub(crate) fn new() -> Self {
+    Self::default()
+  }
+
+  /// Get a reference to a state object by its id
+  pub fn acquire<T: State>(&mut self, id: impl Hash) -> Option<&T> {
+    let id = hash_local(id, &self.id_stack);
+    self.active_ids.insert(id);
+    self.state.get(&id).unwrap().downcast_ref::<T>()
+  }
+
+  /// Get a reference to a state object by its id or insert a new one
+  pub fn acquire_or_insert<T: State>(&mut self, id: impl Hash, state: T) -> &T {
+    let id = hash_local(id, &self.id_stack);
+    self.state.entry(id)
+      .or_insert_with(|| Box::new(state))
+      .downcast_ref::<T>().unwrap()
+  }
+
+  /// Get a reference to a state object by its id or insert a new default one
+  pub fn acquire_or_default<T: State + Default>(&mut self, id: impl Hash) -> &T {
+    let id = hash_local(id, &self.id_stack);
+    self.state.entry(id)
+      .or_insert_with(|| Box::<T>::default())
+      .downcast_ref::<T>().unwrap()
+  }
+
+  /// Get a mutable reference to a state object by its id
+  pub fn acquire_mut<T: State>(&mut self, id: impl Hash) -> Option<&mut T> {
+    let id = hash_local(id, &self.id_stack);
+    self.active_ids.insert(id);
+    self.state.get_mut(&id).unwrap().downcast_mut::<T>()
+  }
+
+  /// Get a mutable reference to a state object by its id or insert a new one
+  pub fn acquire_mut_or_insert<T: State>(&mut self, id: impl Hash, state: T) -> &mut T {
+    let id = hash_local(id, &self.id_stack);
+    self.state.entry(id)
+      .or_insert_with(|| Box::new(state))
+      .downcast_mut::<T>().unwrap()
+  }
+
+  /// Get a mutable reference to a state object by its id or insert a new default one
+  pub fn acquire_mut_or_default<T: State + Default>(&mut self, id: impl Hash) -> &mut T {
+    let id = hash_local(id, &self.id_stack);
+    self.state.entry(id)
+      .or_insert_with(|| Box::<T>::default())
+      .downcast_mut::<T>().unwrap()
+  }
+
+  /// Temporarily forget about current id stack, and use an empty one (within the context of the closure)
+  ///
+  /// Can be useful for state management of non-hierarchical objects, e.g. popups
+  pub fn global<R>(&mut self, f: impl FnOnce(&mut Self) -> R) -> R {
+    self.standby.clear();
+    std::mem::swap(&mut self.id_stack, &mut self.standby);
+    let ret = f(self);
+    std::mem::swap(&mut self.id_stack, &mut self.standby);
+    ret
+  }
+
+  /// Scope the state repo
+  ///
+  /// Anything pushed or popped will be discarded after the closure,
+  /// and the stack will be restored to its previous state
+  pub fn scope<R>(&mut self, f: impl FnOnce(&mut Self) -> R) -> R {
+    self.standby.clear();
+    self.standby.extend(self.id_stack.iter().copied());
+    let ret = f(self);
+    std::mem::swap(&mut self.id_stack, &mut self.standby);
+    ret
+    //XXX: this is super efficient, but works only for pushes, if anything is popped, it will be lost
+    // let len = self.id_stack.len();
+    // let ret = f(self);
+    // self.id_stack.truncate(len);
+  }
 }