Redesign iced_wgpu layering architecture

graphics/src/layer.rs

@@ -0,0 +1,47 @@
+pub trait Layer {
+    type Cache;
+
+    fn new() -> Self;
+
+    fn clear(&mut self);
+}
+
+pub struct Recorder<T: Layer> {
+    layers: Vec<T>,
+    caches: Vec<T::Cache>,
+    stack: Vec<Kind>,
+    current: usize,
+}
+
+enum Kind {
+    Fresh(usize),
+    Cache(usize),
+}
+
+impl<T: Layer> Recorder<T> {
+    pub fn new() -> Self {
+        Self {
+            layers: vec![Layer::new()],
+            caches: Vec::new(),
+            stack: Vec::new(),
+            current: 0,
+        }
+    }
+
+    pub fn fill_quad(&mut self) {}
+
+    pub fn push_cache(&mut self, cache: T::Cache) {
+        self.caches.push(cache);
+    }
+
+    pub fn clear(&mut self) {
+        self.caches.clear();
+        self.stack.clear();
+
+        for mut layer in self.layers {
+            layer.clear();
+        }
+
+        self.current = 0;
+    }
+}