 To solve the issues of transferring information from the original game 's engine to the Saber engine , the developers looked at how they used the third @-@ party Havok physics engine to handle object positioning , velocities , and collisions . Saber created a proxy of every object in the Halo engine to transfer into the Saber engine , meaning that the game 's original programming remained unchanged . The game 's ability to alternate between the legacy and remastered graphics engines in the campaign was made possible by the rendering engine developed by Saber Interactive . The technology allowed the developers to update Halo : Combat Evolved 's visuals and preserve the original gameplay . Originally , players would have chosen which graphical presentation to play from the main menu . The in @-@ game toggle feature quickly became a talking point among the developers , who pushed for it to be available to other players . Since the ability to switch between classic version and remastered version was provided to players , both engines work simultaneously to retain the spontaneity of game . This approach caused several problems , including collision issues — because objects and environments in the original game were of a lower resolution with fewer polygons , higher @-@ resolution visuals in the Saber engine could deviate from the original significantly . As the original game 's geometry was used as the basis for collisions , in some cases characters could appear to walk through or above terrain , weapons could drop through the ground , and bullets would appear to be deflected by nothing . The sheer number of these issues , combined with the desire to keep the original gameplay intact , forced Saber to use a variety of approaches to fix the problems , including making tools for artists to visualize height differences and creating intermediate geometry . In some cases , the artists developed other ways of keeping to the same collision data while updating the visuals by changing the actual object — turning a blocky , low @-@ polygon rock into an angular Forerunner structure avoided the collision issues . 
