testbed: refine a couple of components

testbed/component/position_component.h

@@ -4,8 +4,6 @@
 
 namespace testbed {
 
-struct position_component {
-    SDL_FPoint point;
-};
+struct position_component: SDL_FPoint {};
 
 } // namespace testbed

testbed/component/rect_component.h

@@ -4,8 +4,6 @@
 
 namespace testbed {
 
-struct rect_component {
-    SDL_FRect area;
-};
+struct rect_component: SDL_FRect {};
 
 } // namespace testbed

testbed/system/rendering_system.cpp

@@ -17,7 +17,7 @@ void rendering_system(entt::registry &registry, const context &ctx) {
     SDL_RenderClear(ctx);
 
     for(auto [entt, pos, rect]: registry.view<renderable_component, position_component, rect_component>().each()) {
-        SDL_FRect elem{rect.area.x + pos.point.x, rect.area.y + pos.point.y, rect.area.w, rect.area.h};
+        SDL_FRect elem{rect.x + pos.x, rect.y + pos.y, rect.w, rect.h};
         SDL_SetRenderDrawColor(ctx, 255u, 255u, 255u, SDL_ALPHA_OPAQUE);
         SDL_RenderRect(ctx, &elem);
     }