Did You Know? – Roll for Damage!

  • Nov 27, 2019
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  • By: Parker Wilhem

After 25 years, a series like DOOM is guaranteed to collect its share of fun facts and interesting trivia. Thankfully, you don’t have to be the world’s most dedicated fan or a development insider to learn some of the coolest stuff about this franchise – you have us!


Damage in DOOM (1993) is calculated like dice rolls in a tabletop RPG

Members of the Slayers Club may already know Dungeons & Dragons’ influence on the original DOOM. However, not many also know that the shooter that started it all has another tie to pencil-and-paper roleplaying games: its damage system.

You ever notice that sometimes a Zombieman goes down in two Pistol shots, but other times it’s three? It’s a small difference, but this is because damage from the original DOOM’s weapons and demon attacks are calculated using random values and constants – or to oversimplify it, a dice roll.

Using a 256-byte static table, DOOM (1993) features a pseudorandom number generator that breathes life into the game, be it variable enemy behavior, light flickering, sounds effects and attack damage. To see how DOOM runs without it, Software engineer Johnathan Dowland recorded a video of the game running deterministically and the results are fascinating:

Going back to the Pistol versus the Zombieman, the handgun uses a formula that picks a random amount of damage and multiplies it by a constant. For example, the Pistol’s damage is coded as “random(1,3)*5”, aka ‘choose a number between one and three and multiply it by five’ each time the Pistol hits its target.

Does this make DOOM a game of RNG? Not at all! The Zombieman has a fixed amount of health and the difference between rolling only ones (a 3.7% probability, by the way) and dealing the most damage possible is four shots instead of two, which only amounts to about one extra second of firing.

Even bigger, more complex weapons like the Shotgun (which calculates spread with multiple rolls at once) or the BFG 9000 (which has a special formula for its massive blast radius) don’t have enough variance to punish unlucky players. At the end of the day, DOOM is still DOOM: your tactical skill, speed and resource management is what decides the difference between victory or becoming demon chow!