add comments for FxEngine.h

src/FxEngine/FxEngine.h

@@ -7,11 +7,38 @@
 extern double FE_dh,FE_dv,FE_roulis;
 extern FE_position FE_user;
 
+/*** FE_new_frame()
+ * This function displays las frame content and prepares the next frame
+ * Then, you have to use this in that order :
+ * while (1) {
+ * FE_new_frame()
+ * calculating...
+ * displaying model
+ * post rendering functions
+ * }
+**/
 void FE_new_frame(void); // calls move function
+
+/** FE_get_fps_current()
+ * return a fps number based on the last frame
+**/
 unsigned int  FE_get_fps_current(void);
+
+/** FE_get_fps_min()
+ * return minimal fps number since the addin started
+**/
 unsigned int  FE_get_fps_min(void);
+
+/** FE_get_fps_max()
+ * return maximal fps number since the addin started
+**/
 unsigned int  FE_get_fps_max(void);
-char* FE_fps_get_history(void);
+
+/** FE_get_fps_history()
+ * returns minimal, current and maximal fps number since the addin started
+ * the type is a char* and the fps are set using its format : min/current/max
+**/
+char* FE_get_fps_history(void);
 
 
 #endif