Added love.graphics.origin(): resets the coordinate system (replaces the current transformation matrix with the identity)

--HG--
branch : love.graphics.origin

src/modules/graphics/opengl/Graphics.cpp

@@ -207,7 +207,6 @@ void Graphics::reset()
 void Graphics::clear()
 {
 	glClear(GL_COLOR_BUFFER_BIT);
-	glLoadIdentity();
 }
 
 void Graphics::present()
@@ -1117,6 +1116,11 @@ void Graphics::shear(float kx, float ky)
 	glMultMatrixf((const GLfloat *)t.getElements());
 }
 
+void Graphics::origin()
+{
+	glLoadIdentity();
+}
+
 bool Graphics::hasFocus() const
 {
 	return currentWindow->hasFocus();

src/modules/graphics/opengl/Graphics.h

@@ -510,6 +510,7 @@ public:
 	void scale(float x, float y = 1.0f);
 	void translate(float x, float y);
 	void shear(float kx, float ky);
+	void origin();
 
 	bool hasFocus() const;
 private:

src/modules/graphics/opengl/wrap_Graphics.cpp

@@ -1250,6 +1250,12 @@ int w_shear(lua_State *L)
 	return 0;
 }
 
+int w_origin(lua_State *L)
+{
+	instance->origin();
+	return 0;
+}
+
 int w_hasFocus(lua_State *L)
 {
 	luax_pushboolean(L, instance->hasFocus());
@@ -1352,6 +1358,7 @@ static const luaL_Reg functions[] =
 	{ "scale", w_scale },
 	{ "translate", w_translate },
 	{ "shear", w_shear },
+	{ "origin", w_origin },
 
 	{ "hasFocus", w_hasFocus },
 

src/modules/graphics/opengl/wrap_Graphics.h

@@ -110,6 +110,7 @@ int w_rotate(lua_State *L);
 int w_scale(lua_State *L);
 int w_translate(lua_State *L);
 int w_shear(lua_State *L);
+int w_origin(lua_State *L);
 int w_hasFocus(lua_State *L);
 extern "C" LOVE_EXPORT int luaopen_love_graphics(lua_State *L);