Initial Commit with small working example.

.gitignore

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+a.out
+*~

Ball.h

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+#ifndef BALL_H
+#define BALL_H
+
+#include "GraphicsObject.h"
+//#include "PhysicsObject.h"
+
+class Ball : public GraphicsObject
+{
+public:
+	Ball() : GraphicsObject(&Ball::SetX, this) // pointer to self (specific instance)
+		{
+			instance_num = ++instance_counter;
+		}
+	static void SetX(int &x, void *instance)
+		{
+			Ball *ball = static_cast<Ball*>(instance);
+			ball->x = ball->instance_num; // prove we're accessing the right one
+			return;
+		}
+
+private:
+	static int instance_counter;
+	int instance_num;
+};
+
+int Ball::instance_counter = 0;
+
+#endif

GraphicsObject.h

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+#ifndef GRAPHICSOBJECT_H
+#define GRAPHICSOBJECT_H
+
+class GraphicsObject
+{
+public:
+	// 2nd arg: pointer to callback function that takes a reference to an int as an argument
+	GraphicsObject(int set_x)
+		{
+			x = set_x;
+			user_data = NULL;
+			callback = NULL; // function pointer
+		}
+	GraphicsObject(void (*set_callback)(int&, void*), void *set_user_data)
+		{
+			x = 0;
+			user_data = set_user_data;
+			callback = set_callback; // function pointer
+		}
+	int X()
+		{
+			// If you are SUPPOSED to callback, ...
+			if(callback)
+				// ... do so to ask for the new X value
+				callback(x, user_data);
+			return x; // either this was just set by callback, or it was always set by constructor.
+		}
+//private:
+	int x;
+	void *user_data;
+private:
+	void (*callback)(int&, void*);
+};
+
+#endif

GraphicsSystem.h

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+#ifndef GRAPHICSSYSTEM_H
+#define GRAPHICSSYSTEM_H
+
+#include <vector>
+
+#include "GraphicsObject.h"
+
+class GraphicsSystem
+{
+public:
+	void AddObject(GraphicsObject *obj)
+		{
+			objects.push_back(obj);
+		}
+
+//private:
+	std::vector<GraphicsObject*> objects;
+};
+
+#endif

PhysicsObject.h

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+#ifndef PHYSICSOBJECT_H
+#define PHYSICSOBJECT_H
+
+#include "IPhysics.h"
+
+class PhysicsObject
+	: public IPhysics
+{
+public:
+	PhysicsObject() : IPhysics(&x) {}
+	int GetX() { Update(); return x; }
+private:
+	int x;
+};
+
+#endif

build

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+clang++ main.cpp --std=c++11

main.cpp

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+#include <iostream>
+
+#include "GraphicsSystem.h"
+
+#include "GraphicsObject.h"
+#include "Ball.h"
+
+int main(int argc, char *argv[])
+{
+	GraphicsSystem system;
+
+	GraphicsObject graphics_obj(7);
+	system.AddObject(&graphics_obj);
+	Ball ball1;
+	system.AddObject(&ball1);
+	Ball ball2;
+	system.AddObject(&ball2);
+
+	for(auto obj : system.objects)
+		for(auto i = 0; i < 5; ++i)
+			std::cout << obj->X() << std::endl;
+}