//// 3.4.1 Deriving Maps ////Okay, so we have our object manager. Now we need a class to handler rendering mapsand such. First, we'll need another datastructure for each tile:struct cTile : public cObj {	// since our maps are stored with more than one tile per surface (HOPEFULLY) 	// we need to put the texture coordinates for the tile we want to use. We'll	// write a map loader later to handle loading this crap from a file, and much	// later we'll write a map designer app to make the map file to make the maps.	// Yay.	int t_x, t_y, t_w, t_h;	// boolean flag indicating whether units may move through it	bool passable;};Ugh, I've been thinking. How will we know what to do when a user clicks a unit,then right-clicks a map location? I'm thinking a couple possibilities right now:	- Write a callback function which changes a "mouse state" (bad)	- In the case of a right-click, pass back a move-to position struct, except	  transformed from screen coordinates to world coordinates. (good)So I guess this means we need a position struct (which, in all honesty, can be used to derive some other stuff previously discussed, but foo.)struct cXYPos {	float p_x, p_y; };Okies, so now that we have something to pass back (if there is a unit selected, whichis handled by the parent Game State object) we can move on:class cMap : public cObjMan, cClickable {protected:	// no need to have a container with all the tiles - that's automagically	// generated when the compiler works its template magic. But we DO have	// our tile list (cMap::m_Objs) floating around.	// since our map is (hopefully) larger than the screen, we'll need to store	// the offset values. We'll use these when we render the map to transform	// all of the tiles from local to screen space, and also use them to clip	// tiles that are offscreen.	int m_offX, m_offY;public:		// all of the functions which have been previously explained. Should be pretty	// self-explainatory. All inheritec from cObjMan.	// add tile	// get tile	// rem tile	// render	// update		// here's how we move the Map around - by allowing indirect access to the	// offset variables.	virtual void moveMap(int incX, int incY);	// might as well throw in the other accessor function:	virtual void getOffset(int& offX, int& offY);	// now we have a couple more tidbits to throw in, primarily user interaction with	// the map. Since the unit manager handles all the fancy mouse-unit coldet, our	// job here is pretty simple - just transform screen space to local space :)	// inherited from cClickable.	virtual cXYPos onClick(int mouseX, int mouseY);};And that's about it for the map class. Time to write the unit manager!