Call of Duty 4: Modern Warfare will run on a proprietary engine, and has next generation features such as true world-dynamic lighting, bloom effects, dynamic shadows and depth-of-field. "Bullet Penetration" is calculated by the engine, taking into account things such as surface type and entity thickness. Certain objects, such as cars, will be destructible (it should be noted that the environments are still indestructible). This makes distinguishing cover from concealment important, as meager protection such as wooden fences, thin walls and such will no longer provide sufficient protection. The bullet's speed and stopping power will be decreased after penetrating an object, and this decrease is calculated realistically depending on the thickness and surface of the object penetrated. The game also makes use of a physics engine, which was not implemented in previous Call of Duty titles for the PC. Death Animations are a combination of pre-set animations and ragdoll physics. Some mistook the game's graphics to be DirectX 10 based, but it is stated that the graphics use DirectX 9.