Move `layer::Cached` to its own module

1 files changed, 82 insertions, 0 deletions

diff --git a/wgpu/src/widget/canvas/layer/cached.rs b/wgpu/src/widget/canvas/layer/cached.rs
new file mode 100644
index 00000000..c6741372
--- /dev/null
+++ b/wgpu/src/widget/canvas/layer/cached.rs
@@ -0,0 +1,82 @@
+use crate::{
+    canvas::{layer::Drawable, Frame, Layer},
+    triangle,
+};
+
+use iced_native::Size;
+use std::cell::RefCell;
+use std::marker::PhantomData;
+use std::sync::Arc;
+
+#[derive(Debug)]
+pub struct Cached<T: Drawable> {
+    input: PhantomData<T>,
+    cache: RefCell<Cache>,
+}
+
+#[derive(Debug)]
+enum Cache {
+    Empty,
+    Filled {
+        mesh: Arc<triangle::Mesh2D>,
+        bounds: Size,
+    },
+}
+
+impl<T> Cached<T>
+where
+    T: Drawable + std::fmt::Debug,
+{
+    pub fn new() -> Self {
+        Cached {
+            input: PhantomData,
+            cache: RefCell::new(Cache::Empty),
+        }
+    }
+
+    pub fn clear(&mut self) {
+        *self.cache.borrow_mut() = Cache::Empty;
+    }
+
+    pub fn with<'a>(&'a self, input: &'a T) -> impl Layer + 'a {
+        Bind {
+            layer: self,
+            input: input,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Bind<'a, T: Drawable> {
+    layer: &'a Cached<T>,
+    input: &'a T,
+}
+
+impl<'a, T> Layer for Bind<'a, T>
+where
+    T: Drawable + std::fmt::Debug,
+{
+    fn draw(&self, current_bounds: Size) -> Arc<triangle::Mesh2D> {
+        use std::ops::Deref;
+
+        if let Cache::Filled { mesh, bounds } =
+            self.layer.cache.borrow().deref()
+        {
+            if *bounds == current_bounds {
+                return mesh.clone();
+            }
+        }
+
+        let mut frame = Frame::new(current_bounds.width, current_bounds.height);
+        self.input.draw(&mut frame);
+
+        let mesh = Arc::new(frame.into_mesh());
+
+        *self.layer.cache.borrow_mut() = Cache::Filled {
+            mesh: mesh.clone(),
+            bounds: current_bounds,
+        };
+
+        mesh
+    }
+}