added const qualifier to box stamp method

demo/Demo.cpp

@@ -16,7 +16,7 @@
   classes, private and public class members, pixel class iterator, sprite
   movement history, input history, use seconds instead of milliseconds, store
   a node's animations in list, frame object for sprite class, inline short
-  functions, add box2d to library
+  functions, add box2d to library, load in separate thread and display progress
 
   :) SWEATY HANDS :) OILY SNACKS :) AND BAD HYGIENE :)
 

src/Box.cpp

@@ -293,7 +293,7 @@ void Box::move(const glm::vec2& delta)
     set_y(get_y() + delta.y);
 }
 
-Box Box::stamp(const glm::vec2& delta)
+Box Box::stamp(const glm::vec2& delta) const
 {
     Box clone = *this;
     clone.move(delta);

src/Box.hpp

@@ -65,7 +65,7 @@ struct Box : SDL_FRect
     void expand(glm::vec2, bool = false);
     void expand(float, bool = false);
     void move(const glm::vec2&);
-    Box stamp(const glm::vec2&);
+    Box stamp(const glm::vec2&) const;
     bool collide(const glm::vec2&) const;
     bool collide(const Segment&, glm::vec2* = nullptr) const;
     bool collide(const Segment&, glm::vec2&) const;