Articles :: Mirror’s Edge PhysX Review ::

Doc Overclock · 01-26-2009 · Category: Tech-planations

Mirror's Edge PhysX Effects

  • Physically Simulated Glass
  • Physically Simulated Smoke
  • Physically Simulated Cloth
  • Physically Simulated Wind
  • Simulated Debris and weapons particles

Glass in most games is shot at then disappears from the world. You might get as econd or two of glass on the floor but in the vast majority of games you shoot glass it shatters and that's it. On a card with PhysX, Mirror's Edge takes this to the next level. Glass in the game is physically simulated, allowing the player to punch the glass, shoot the glass, and interact with the glass in many ways. The glass is persistent; meaning if it breaks it falls and stays on the ground without disappearing. Here are two shots, one with PhysX on and one with it disabled. Note the glass shards on the floor.

No PhysX


Physically Simulated Smoke is something that is missing from games. While many games have smoke to enhance the visual feel of the game, graphical smoke has no effect on the environment or on the characters in a game. Mirror's Edge uses physically simulated smoke. This smoke interacts with the character and environment. As the player moves through smoke they leave a trail. The helicopter gunships rotors blow smoke over chimneys and vents. Wind based physics is another of the features of the Mirror's Edge game engine. In addition to the smoke interaction trains in the game cause banners to sway when passing by. Helicopters stir up dust and debris. Take a look at the difference between these two screenshots. One has smoke that kind of willows. The second screenshot has no smoke at all on the floor.

No Physx

PhysX Smoke

If you have seen some of the demos for the PhysX engine, you know that cloth can be interacted with in an engine that uses graphics based physics. In Mirror's Edge cloth simulations are used for curtains, blinds and construction tarp. Banners and cloths in the game respond to trains passing or helicopters and weapon fire. Cloth can be tangled up onto the player and dragged across the scene. This is the difference between games that use hardware physics and those that use the CPU to run the physics. While these effects can be done they are generally very slow on the processor alone. The graphics card in Mirror's Edge uses hardware physics to do all of these wonderful effects. Here's a screenshot of a helicopter hovering over some banners. Notice that the banners are flat with a few ripples. The second screenshot shows a banner flapping.

Banner no PhysX

Banner PhysX

Debris in games usually disappears after a second or two. With Mirror's Edge, the game's engine allows you to shoot at objects made out of concrete, throw debris that bounces on the ground and stays there. Persistent debris allows the player to interact with it. Firing a weapon at a metal floor will cause sparks which can bounce off objects in the game. Game physics like these and more exist throughout the game Mirror's Edge. Hardware based physics, when done right can make a game more immersive, and make the game more realistic to the player as they see objects interact realistically with other objects in a game. Here's a screenshot of some debris from bullets hitting the floor. The second shot is the non-PhysX shot where there is no debris.

No PhysX Debris

PhysX Debris


  1. Introduction
  2. PhysX Features
  3. Mirror's Edge PhysX Effects
  4. Performance in Mirror's Edge
  5. Conclusion