Created the TileSheet class

This is incomplete on it's own, but used as part of the whole map system,
it should work well. This class keeps track of various, seemingly
unrelated states, which are used as part of the larger map system.

Also, fixed Region's members being public.

editor/tile_sheet.cpp

@@ -0,0 +1,68 @@
+#include "tile_sheet.hpp"
+
+#include <algorithm>
+#include <stdexcept>
+
+static inline std::string truncatePath(std::string pathname) {
+	//TODO: move this into a utilities module?
+	return std::string(
+		std::find_if(
+			pathname.rbegin(),
+			pathname.rend(),
+			[](char ch) -> bool {
+				//windows only
+				return ch == '/' || ch == '\\';
+//				//unix only
+//				return ch == '/';
+			}).base(),
+		pathname.end());
+}
+
+SDL_Surface* TileSheet::LoadSurface(std::string fname, Uint16 w, Uint16 h) {
+	//setup the image
+	image.LoadSurface(fname);
+	image.SetClipW(w);
+	image.SetClipH(h);
+
+	//get the tile counts
+	xCount = image.GetSurface()->w / w;
+	yCount = image.GetSurface()->h / h;
+	totalCount = xCount * yCount;
+
+	//cache the name
+	name = truncatePath(fname);
+}
+
+SDL_Surface* TileSheet::SetSurface(SDL_Surface* const ptr, Uint16 w, Uint16 h) {
+	//setup the image
+	image.SetSurface(ptr);
+	image.SetClipW(w);
+	image.SetClipH(h);
+
+	//get the tile counts
+	xCount = image.GetSurface()->w / w;
+	yCount = image.GetSurface()->h / h;
+	totalCount = xCount * yCount;
+}
+
+SDL_Surface* TileSheet::GetSurface() {
+	return image.GetSurface();
+}
+
+void TileSheet::FreeSurface() {
+	image.FreeSurface();
+	totalCount = xCount = yCount = 0;
+}
+
+void TileSheet::DrawTo(SDL_Surface* const dest, int x, int y, int tileIndex) {
+	if (!InRange(tileIndex)) {
+		throw(std::runtime_error("Tile index out of range of Tile Sheet"));
+	}
+	Sint16 clipX = tileIndex % xCount * image.GetClipW();
+	Sint16 clipY = tileIndex / xCount * image.GetClipH();
+
+	image.SetClipX(clipX);
+	image.SetClipY(clipY);
+
+	image.DrawTo(dest, x, y);
+}