Introduce a Driver abstraction to encapsulate the SimState and the Renderers

src/render.rs

@@ -229,21 +229,25 @@ impl MultiRenderer {
     pub fn new() -> Self {
         Default::default()
     }
-    pub fn with<R: Renderer + 'static>(mut self, r: R) -> Self {
+    pub fn push<R: Renderer + 'static>(&mut self, r: R) {
         self.renderers.push(Box::new(r));
+    }
+    pub fn with<R: Renderer + 'static>(mut self, r: R) -> Self {
+        self.push(r);
         self
     }
 }
 
 impl Renderer for MultiRenderer {
+    fn render(&mut self, state: &SimState) {
+        if self.renderers.len() != 0 {
+            self.render_with_image(state, &state.to_image());
+        }
+    }
+
     fn render_with_image(&mut self, state: &SimState, im: &RgbImage) {
         for r in &mut self.renderers {
             r.render_with_image(state, im);
         }
     }
 }
-
-pub struct NullRenderer;
-impl Renderer for NullRenderer {
-    fn render(&mut self, state: &SimState) {}
-}