Animation (#355)

include/ftxui/component/component_base.hpp

@@ -13,6 +13,10 @@ class Delegate;
 class Focus;
 struct Event;
 
+namespace animation {
+class Params;
+}  // namespace animation
+
 class ComponentBase;
 using Component = std::shared_ptr<ComponentBase>;
 using Components = std::vector<Component>;
@@ -42,6 +46,9 @@ class ComponentBase {
   // Returns whether the event was handled or not.
   virtual bool OnEvent(Event);
 
+  // Handle an animation step.
+  virtual void OnAnimation(animation::Params& params);
+
   // Focus management ----------------------------------------------------------
   //
   // If this component contains children, this indicates which one is active,