Add `Runtime` concept to abstract caching

4 files changed, 118 insertions, 85 deletions

diff --git a/src/interface.rs b/src/interface.rs
deleted file mode 100644
index 6c4982e5..00000000
--- a/src/interface.rs
+++ /dev/null
@@ -1,77 +0,0 @@
-use std::hash::Hasher;
-use stretch::result;
-
-use crate::{Element, Event, Layout, MouseCursor, Point};
-
-pub struct Interface<'a, Message, Renderer> {
-    hash: u64,
-    root: Element<'a, Message, Renderer>,
-    layout: result::Layout,
-}
-
-pub struct Cache {
-    hash: u64,
-    layout: result::Layout,
-}
-
-impl<'a, Message, Renderer> Interface<'a, Message, Renderer> {
-    pub fn compute(
-        root: Element<'a, Message, Renderer>,
-        renderer: &Renderer,
-    ) -> Interface<'a, Message, Renderer> {
-        let hasher = &mut crate::Hasher::default();
-        root.hash(hasher);
-
-        let hash = hasher.finish();
-        let layout = root.compute_layout(renderer);
-
-        Interface { hash, root, layout }
-    }
-
-    pub fn compute_with_cache(
-        root: Element<'a, Message, Renderer>,
-        renderer: &Renderer,
-        cache: Cache,
-    ) -> Interface<'a, Message, Renderer> {
-        let hasher = &mut crate::Hasher::default();
-        root.hash(hasher);
-
-        let hash = hasher.finish();
-
-        let layout = if hash == cache.hash {
-            cache.layout
-        } else {
-            root.compute_layout(renderer)
-        };
-
-        Interface { hash, root, layout }
-    }
-
-    pub fn on_event(&mut self, event: Event, cursor_position: Point, messages: &mut Vec<Message>) {
-        let Interface { root, layout, .. } = self;
-
-        root.widget
-            .on_event(event, Self::layout(layout), cursor_position, messages);
-    }
-
-    pub fn draw(&self, renderer: &mut Renderer, cursor_position: Point) -> MouseCursor {
-        let Interface { root, layout, .. } = self;
-
-        let cursor = root
-            .widget
-            .draw(renderer, Self::layout(layout), cursor_position);
-
-        cursor
-    }
-
-    pub fn cache(self) -> Cache {
-        Cache {
-            hash: self.hash,
-            layout: self.layout,
-        }
-    }
-
-    fn layout(layout: &result::Layout) -> Layout<'_> {
-        Layout::new(layout, Point::new(0.0, 0.0))
-    }
-}
diff --git a/src/layout.rs b/src/layout.rs
index 011f859a..481b4166 100644
--- a/src/layout.rs
+++ b/src/layout.rs
@@ -19,8 +19,16 @@ pub struct Layout<'a> {
 }
 
 impl<'a> Layout<'a> {
-    pub(crate) fn new(layout: &'a result::Layout, parent_position: Point) -> Self {
-        let position = parent_position + Vector::new(layout.location.x, layout.location.y);
+    pub(crate) fn new(layout: &'a result::Layout) -> Self {
+        Self::with_parent_position(layout, Point::new(0.0, 0.0))
+    }
+
+    fn with_parent_position(
+        layout: &'a result::Layout,
+        parent_position: Point,
+    ) -> Self {
+        let position =
+            parent_position + Vector::new(layout.location.x, layout.location.y);
 
         Layout { layout, position }
     }
@@ -47,9 +55,8 @@ impl<'a> Layout<'a> {
     /// [`Layout`]: struct.Layout.html
     /// [`Node`]: struct.Node.html
     pub fn children(&'a self) -> impl Iterator<Item = Layout<'a>> {
-        self.layout
-            .children
-            .iter()
-            .map(move |layout| Layout::new(layout, self.position))
+        self.layout.children.iter().map(move |layout| {
+            Layout::with_parent_position(layout, self.position)
+        })
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 9c7eed8d..6ea3e60d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -9,13 +9,13 @@ pub mod widget;
 mod element;
 mod event;
 mod hasher;
-mod interface;
 mod layout;
 mod mouse_cursor;
 mod node;
 mod point;
 mod rectangle;
 mod renderer;
+mod runtime;
 mod style;
 mod vector;
 
@@ -25,13 +25,13 @@ pub use stretch::{geometry::Size, number::Number};
 pub use element::Element;
 pub use event::Event;
 pub use hasher::Hasher;
-pub use interface::Interface;
 pub use layout::Layout;
 pub use mouse_cursor::MouseCursor;
 pub use node::Node;
 pub use point::Point;
 pub use rectangle::Rectangle;
 pub use renderer::Renderer;
+pub use runtime::{Interface, Runtime};
 pub use style::{Align, Justify, Style};
 pub use vector::Vector;
 pub use widget::*;
diff --git a/src/runtime.rs b/src/runtime.rs
new file mode 100644
index 00000000..f8a5aaa3
--- /dev/null
+++ b/src/runtime.rs
@@ -0,0 +1,103 @@
+use crate::{Column, Element, Event, Layout, MouseCursor, Point};
+
+use std::hash::Hasher;
+use stretch::result;
+
+pub struct Runtime {
+    cache: Cache,
+    events: Vec<Event>,
+    cursor_position: Point,
+}
+
+impl Runtime {
+    pub fn new() -> Runtime {
+        // We use this as a placeholder to initialize the cache.
+        // This way, we can avoid the overhead of using an `Option`
+        // in `compute`.
+        let root: Element<'_, (), ()> = Column::new().into();
+
+        let hasher = &mut crate::Hasher::default();
+        root.hash(hasher);
+
+        Runtime {
+            cache: Cache {
+                hash: hasher.finish(),
+                layout: root.compute_layout(&()),
+            },
+            events: Vec::new(),
+            cursor_position: Point::new(0.0, 0.0),
+        }
+    }
+
+    pub fn on_event(&mut self, event: Event) {
+        self.events.push(event);
+    }
+
+    pub fn compute<'a, Message, Renderer>(
+        &'a mut self,
+        root: Element<'a, Message, Renderer>,
+        renderer: &Renderer,
+    ) -> Interface<'a, Message, Renderer> {
+        let hasher = &mut crate::Hasher::default();
+        root.hash(hasher);
+
+        let hash = hasher.finish();
+
+        if hash != self.cache.hash {
+            self.cache = Cache {
+                hash,
+                layout: root.compute_layout(renderer),
+            };
+        }
+
+        Interface {
+            root,
+            layout: &self.cache.layout,
+            events: &mut self.events,
+            cursor_position: self.cursor_position,
+        }
+    }
+}
+
+struct Cache {
+    hash: u64,
+    layout: result::Layout,
+}
+
+pub struct Interface<'a, Message, Renderer> {
+    root: Element<'a, Message, Renderer>,
+    layout: &'a result::Layout,
+    events: &'a mut Vec<Event>,
+    cursor_position: Point,
+}
+
+impl<'a, Message, Renderer> Interface<'a, Message, Renderer> {
+    pub fn update(&mut self) -> Vec<Message> {
+        let mut messages = Vec::new();
+
+        for event in self.events.drain(..) {
+            self.root.widget.on_event(
+                event,
+                Layout::new(&self.layout),
+                self.cursor_position,
+                &mut messages,
+            );
+        }
+
+        messages
+    }
+
+    pub fn draw(
+        &self,
+        renderer: &mut Renderer,
+        cursor_position: Point,
+    ) -> MouseCursor {
+        let cursor = self.root.widget.draw(
+            renderer,
+            Layout::new(self.layout),
+            cursor_position,
+        );
+
+        cursor
+    }
+}