THE PHYSICS OF HALFLIFE 2 BY LEWIS JORDAN

THE PHYSICS OF HALF-LIFE 2 BY LEWIS JORDAN AND KRISTIYAN STOYANOV

ENGINE DIFFERENCES • Half-Life 2 is a linear, story driven, shooter and has run on three engine iterations over throughout its lifetime Although this is the case, it is usually categorised by either ‘Old Engine’ or New ‘Engine’. • First there was Source Engine (‘Old Engine’, builds 2187 – 4044) • Then there was the Orange. Box Engine (‘New Engine’, builds 4259 – 5135) • Currently there is the Steampipe Engine for the steam version of Half-Life 2 (Still ‘New Engine’, builds 5298 – current) • The best way to describe a game’s physics is through its unique elements as well as exploits which are known best by the game’s speedrunners

THE GRAVITY GUN (ZERO POINT ENERGY FIELD MANIPULATOR) • Rather than conventional ammunition, the gravity gun uses object in the game as ammunition to launch at enemies. It is also used to move objects in order to complete physics based puzzles • ‘The Gravity Gun has two modes. ‘The primary fire releases an energy blast which punts the targeted object with tremendous force. This is useful for clearing out barriers and moving heavy objects. The secondary fire picks objects up and holds them just ahead of the gun. ’ ([1] Half-Life Wiki, 2018) [1] Half-Life Wiki. (2018). Zero Point Energy Field Manipulator. [online] Available at: http: //half-life. wikia. com/wiki/Zero_Point_Energy_Field_Manipulator [Accessed 30 Jan. 2018].

ENGINE DIFFERENCES • Although the game is still essentially the same, the physics of the game differ greatly depending on the version • Differences from collision detection to environmental force interaction with the player • These differences are mostly known because of their exploitation by speedrunners • Whether this very exploitable engine is good or not depends on point of view. It is bad as it can ruin the immersion, cause game imbalances, etc… But can be good as these glitches have created a long lasting community of players that still enjoy the game years after its release.

OLD ENGINE • In the old engine, there was a movement technique called “bunnyhopping”. The character could maintain their velocity by jumping as soon as they hit the ground. When paired with the fact that the character accelerated faster while strafing left or right, instead of moving forwards or backwards, this allowed players to move very fast indeed. • Players could also overload the physics engine by getting ‘stuck’ inside an object while still being able to jump. Their cumulative jumps while stuck increased their ‘unstuck velocity’ which was all assigned to the character, once they became unstuck, all at once. Again this allowed for rapid movement, the velocity of which could be maintained by “bunnyhopping”.

OLD ENGINE • Every prop, no matter the size, had a collider that the player could interact with. The object is always held in relation to the player and is not affected by gravity, this means that the player can stand on one of these props and use it as a sort of floating platform. This meant that any prop could be used to help the player practically fly by placing the item underneath their feet and jumping. Was fixed in the New Engine by removing colliders from small objects. possible with larger items like barrels) (still

NEW ENGINE (ORANGEBOX AND STEAMPIPE) • In an attempt to fix “bunnyhopping” in the new engine, Valve made it so if the player was going over a certain velocity, a force was added to slow them down. This was exploited by merely turning around in mid-air and jumping to maintain velocity. This ‘fix’, ironically, allowed the player to move even faster than before. Video 1

NEW ENGINE (ORANGEBOX AND STEAMPIPE) • Similar to the ‘stuck’ method of rapid velocity change, there is a way to overload the physics engine in the New Engine which allows you to be launched at a huge velocity. It works by having an object stuck in a closing door or other scripted moving object. A possible explanation is that ‘When this object is being crushed by enormous moving force, it tries to resist by pushing another object from itself. After it gets free, the engine still thinks it's being crushed, and applies the push-from-itself force as soon as it touches an entity. ’ ([2] Wiki. sourceruns. org, 2018) Video 2 [2] Wiki. sourceruns. org. (2018). Super Physics Deformation - Source. Runs Wiki. [online] Available at: https: //wiki. sourceruns. org/wiki/Super_Physics_Deform [Accessed 30 Jan. 2018].

MAIN COMPARISON https: //www. youtube. com/watch? v=nm. Aat. Vmi. Mec

ANY QUESTIONS?

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