I don't know :/

.gitignore

@@ -6,3 +6,4 @@ lib/libbpg*/**/*.a
 lib/libbpg*/bpgdec
 lib/libbpg*/bpgenc
 lib/libbpg*/bpgview
+tags

gameobj.d

@@ -16,6 +16,7 @@
  */
 
 module gameobj;
+import derelict.sdl2.sdl;
 
 interface GameObj {
 	void prepare();
@@ -23,3 +24,19 @@ interface GameObj {
 	void exec();
 	bool wants_to_quit() const;
 }
+
+class GameObjBase : GameObj {
+public:
+	this (SDL_Renderer* parRenderer) {
+		m_renderer = parRenderer;
+		assert(m_renderer);
+	}
+
+protected:
+	SDL_Renderer* renderer() {
+		return m_renderer;
+	}
+
+private:
+	SDL_Renderer* m_renderer;
+}

gameobjjumping.d

@@ -21,14 +21,14 @@ import derelict.sdl2.sdl;
 import texture;
 import std.stdio;
 
-class GameObjJumping : GameObj {
+class GameObjJumping : GameObjBase {
 	//Don't disable this(), it's disable automatically when you define a
 	//custorm constructor.
 	//@disable this();
 
 	//Take the pointer to the renderer and set initial values
 	this (SDL_Renderer* parRenderer) {
-		m_renderer = parRenderer;
+		super(parRenderer);
 		m_wants_to_quit = false;
 	}
 
@@ -39,7 +39,7 @@ class GameObjJumping : GameObj {
 	void prepare() {
 		string texture_name = "bcruiser_normal.bpg";
 		writeln("Loading texture %s", texture_name);
-		m_texture = Texture(texture_name, m_renderer);
+		m_texture = Texture(texture_name, renderer());
 	}
 
 	void destroy() {
@@ -47,9 +47,9 @@ class GameObjJumping : GameObj {
 
 	//This is the function that is called at every frame
 	void exec() {
-		SDL_RenderClear(m_renderer);
+		SDL_RenderClear(renderer());
 		m_texture.draw();
-		SDL_RenderPresent(m_renderer);
+		SDL_RenderPresent(renderer());
 		m_wants_to_quit = do_events();
 	}
 
@@ -59,7 +59,6 @@ class GameObjJumping : GameObj {
 
 private:
 	Texture m_texture;
-	SDL_Renderer* m_renderer;
 	bool m_wants_to_quit;
 }