How Brutal Doom’s Gore Works

“Saved my hide, it did. The alien’s broad back shielded me as its brethren flung their fiery mucus wads; the fireballs burst, spraying flaming, red liquid that dribbled down my dance partner’s legs to pool on the ground, lighting the room with a hellish, red glaze. I fired nine or ten times, finally blowing a hole clean through the alien … a gory loophole through which I turned on the rest.”

Knee Deep in the Dead, Dafydd Ab Hugh and Brad Linaweaver’s novelisation of Doom, is perhaps a little more theatrical than the Doom that played in my head during the summer of 1994. It features a sidekick and talking demons, and dramatised sequences in which protagonist Corporal Flynn Taggart finds ammo and bumps up against walls to find secrets. But it captures something of Doom’s intensely graphic nature. Doom was the first game I played that felt truly fluid and direct.

Playing Brutal Doom [official site] today feels like Doom always did, despite its custom levels and gouts of blood and gore, death animations and chugging live versions of Doom’s MUS originals. It overhauls pretty much every element of the original, and yet it’s the Doom that plays in my memory, amplifying the original’s gore and immediacy to suit a post-COD, Gears of War – heck, Soldier of Fortune – world. For me, the latest version, v20b, reaches a state of the sublime. But while the blood that drips from ceilings and screen-filling viscera are its obvious achievements, something far more prosaic lies at the root of how it works so well.

THE MECHANIC: Hitboxes.

Sergeant_Mark_IV never planned to make a mod as focused as Brutal Doom. A veteran of Warcraft 3 map making (“I had the terrible habit of attempting to make maps that had nothing to do with Warcraft itself, with themes such as World War III and the first Gulf War”), he originally set out to make a crazily ambitious total conversion called ArmageDoom. An unofficial sequel to Doom 2, it was meant to have a campaign representing Earth’s last stand against the demons, 20 weapons, 40 new enemies, drivable vehicles and it got as far as a beta, albeit bug-ridden and with only eight maps and a fraction of the planned features.

It was proving too much to handle, so Sergeant_Mark_IV decided to step back and look at one challenge he was facing: introducing a sniper rifle. “It was a completely redundant weapon, since the firefights usually happens at either close or mid range, and the lack of a headshot system made the accurate shoots have no real use,” he says. But it lodged an idea, that of developing for Doom a hit detection system so enemies would receive different damage values depending on where they were hit.

At the same time, he had a hankering to create a new blood system. Like many Doom mods, ArmageDoom was built on ZDoom, an enhanced port of the original Doom engine to Windows which among many other things adds mouselook, and its gore system borrowed from two gore-producing mods, Nashgore and Ultragore. The Doom engine cannot natively draw decals on floors and ceilings, since floors and ceilings don’t technically exist, but Sergeant_Mark_IV developed a way of simulating decals using flat 3D models.

With the ability to shoot a zombie’s head off and paint the room with explosions of blood, Brutal Doom was born. Testers loved the extra feedback Sergeant_Mark_IV’s prototype gave. Encouraged, he started to pile in more and more features – smoke and fire, reloading, light flares. “It became my obsession,” he says. “I started to add everything that I used to imagine should be in a sequel to Doom 2. It went from ‘student project to learn how to use the engine’ to ‘how I wish Doom 3 was’.”

Brutal Doom’s gore system is built on a single function from Heretic’s source code called A_TossGib. It randomly throws things in random directions and was frequently used by other mods as a way of spawning particles. Over time it was steadily refined to add more control over the properties of these particles, and so in Brutal Doom, every gib, splatter of blood, flame or puff of smoke is a projectile with gravity and ability to bounce so that it interacts with the environment.

As a way of illustrating just how deep Brutal Doom’s gore system goes, and how Sergeant_Mark_IV hacked a hardcoded form of physics into a 23-year-old game, we can look at what happens when you kill an imp with a shotgun. When you click the mouse button, the game sends out a hitscan – traced lines between the player and where they’re facing – to see if it intersects with an object. So far, so vanilla Doom. But when a vanilla Doom monster is just one big rectangular hitbox, Brutal Doom’s have three, the body joined to smaller boxes at the head and legs.

So let’s imagine the shotgun has hit the imp’s legs. The imp’s hitbox spawns small explosions, which are set to only harm the monster that spawns them. The resulting damage is calculated and applied to the imp. If it’s enough to kill it, and the blast is from short enough range, it will jump to an animation frame in which one of its legs is cut off, and then randomly to one of various different sets of frames which include dropping to the floor dead, hopping on one leg for a few seconds before collapsing, or kneeling in agony until it either bleeds out or the player finishes it off.

A torso hit that’s strong enough to kill the imp triggers different responses. If the imp is more than 200 in-game pixels away, it simply dies. Closer hits will push the imp backwards, usually triggering one of two the animations. The first has it flipping through the air and rolling on the ground until it loses momentum (it will therefore continue to roll if on stairs). The second violently throws it backwards; if it hits a wall, it will display a frame of the imp sat on the ground with its back to the wall. More rarely, two alternative animations may be displayed in which the imp loses a limb, or its guts are sent flying out of a hole in its stomach. Going back to our dead imp sitting against the wall, if the wall is a door and it’s opened, the imp will slump to a lying position. Moreover, sitting imp retains its hitboxes, so it can be further mangled if the player keeps shooting it.

Headshot kills do much the same thing. The imp’s jaw might be destroyed, launching jaw and teeth sprites in random directions. Or its forehead might be shown pierced by a bullet and the back of its head given a large exit hole, with brain and blood launched out from it. If they strike a wall, they will slide down it. If the player causes enough damage to push its health to -60 points, the imp’s head will explode, Scanners-style, spawning and launching blood and various bits of skull, brain, teeth and jawbone in all directions.

Hitting a zombie with a rocket leads to yet more scenarios. If the blast lands far enough away that it isn’t killed, it will be knocked out for two seconds. If the zombie should fall more than five metres as a result of a rocket’s concussive blast, it will die on hitting the ground. If the rocket hits the ground close enough to kill the zombie, it will push it up and over obstacles (its sprite shows it burned by the blast, and its eyes will pop out). “It causes a very nice effect when you fire a rocket or grenade inside a bunker-like structure full of humanoid enemies, as they are sent flying away from the windows,” says Sergeant_Mark_IV.

A direct hit will simply blow the zombie apart. Distinguishable gibs are spawned and launched at random directions, including its head and limbs, which can be shot or kicked into smaller pieces. Gibs are set not to bounce, so they stick to walls, and then a second gib replaces them that is launched at a slowly accelerating rate so it slides down.

Sergeant_Mark_IV also controls the amount of blood that sprays around. Severed limbs spawn more than bullet impacts. “Others required deeper investigation of human anatomy,” he says. “Like trying to guess how much blood would fly away if you directly hit humanoid creatures with anti-materiel weaponry.” Only some specific death animations, such as point-blank double blasts with the super shotgun, will send out blood and gibs in specific directions; they otherwise fan out. He has also refined the puddles of blood on the ground, which were larger and denser in early versions than they are in v20b. “I made them look sharper and have a more stained look in favour of improving realism, satisfactory feedback, and improving performance.”

In fact, he’s been doing a lot to tone down the gore since Brutal Doom first appeared. As much as it looks the opposite, the philosophy underlying it is one of balance and restraint; Sergeant_Mark_IV feels Brutal Doom’s success is down to being neither too over-the-top, nor too realistic. “They are a mix of both, an equilibrium between cartoonish violence and gruesome horrors of war. In early versions of Brutal Doom, everything was over the top. Firing a bullet into an zombie’s chest would spawn a fountain of blood, firing at the head would paint the entire room red. It was tasteless, overdone, and got boring fast.”

One could argue that Brutal Doom is tasteless in its entirety. Sergeant_Mark_IV’s apparent enthusiasm for researching real injuries has landed him in some controversy. Then again, Doom was a model of tastelessness before it, and used similar source material. But within all the excess of both Doom and Brutal Doom lies deep rigour, rigour that you can feel in how good they are to play. So, why Doom? “Why not Doom?” says Sergeant_Mark_IV, detailing the ease with which it can be edited and modded. “It’s the greatest game ever made.”

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25 Comments

  1. JakeOfRavenclaw says:

    This is an excellent article :-)

    Brutal Doom is the only game I’ve played in which you can kick a guy’s head off so hard that his brains drip from the ceiling–a dubious distinction, maybe, but I laughed out loud the first time I saw it. The enhanced gore turns levels into deranged physics playgrounds, and the modern touches like jumping and grenades and and being able to finish enemies with a kick are all thoughtfully implemented. I’m willing to give Bethesda’s new Doom the benefit of a doubt until I’m actually playing it, but in a lot of respects Brutal Doom feels like it’s already solved the problem of how to make the old formula feel new again.

  2. Premium User Badge

    heretic says:

    Just watched the trailer on youtube after this article, really cool, need to try it out :)

  3. Vorig says:

    I play almost every doom map/mod with brutal doom if it’s compatible. You get so used to the extra features that the gibbing and blood are just gravy (gravy that you can control in the settings :)

  4. Vorig says:

    Also, check out project brutality for even more weapon/monster changes if you like the cut of brutal doom’s jib.

  5. steves says:

    Why have I never played this?

    And I have £4 of GOG credit from somewhere that runs out next week. Or at least I did have:

    link to gog.com

    Oh, and there’s a “Metal Soundtrack Mod” linked from Brutal Doom. Think I’ll be having that too.

    Looking forward to an noisy & violent bank holiday of unsophisticated old-school murder!

  6. ddaymace says:

    my favorite game mod. makes the footage of new doom look boring.

  7. dethtoll says:

    Ahh, yes. Doom: Harris & Klebold Edition. Has anyone gone through UACLABS.WAD with this yet? link to acolumbinesite.com

  8. Jharakn says:

    Everytime I play brutal doom I encounter some new animation I never knew existed, yesterday a revenant picked up a zombie, went on it for a while then threw its corpse at me, which due to my stunned appreciation of this smacked me straight in a face.

    The attention to detail is staggering in this mod.

  9. tonicer says:

    Brutal Doom is exactly what the modern gaming world needs. Not another generic console game like Doom4, the gaming world needs to get back to computer games everything is better there. If i look at videos of Doom4 i just cry at how they butchered yet another franchise to meet the demands of the console crowd.

    A few other franchises that got butchered are:
    – Duke Nukem
    – Battlefield
    – Counter Strike
    – Call of Duty
    – The Elder Scrolls
    – Far Cry
    – Crysis
    – Rainbow Six
    – Ghost Recon
    – Minecraft

    I think you get the gist of it.

    • Phasma Felis says:

      Minecraft? What? It was PC exclusive for years before they even thought about a console version. When the console ports ran into limitations, they dialed down the ports and left the PC version unchanged.

      • ZombieFX says:

        He probably means the QTE Minecraft games, from Doublefine.
        QTE… Minecraft…
        just say it once out loud… than you know wrong that sounds. (and is)

    • dethtoll says:

      You must be fun at parties.

  10. Chaoslord AJ says:

    Oops never knew it had patched hitboxes in. Let’s replay.

  11. Swanny says:

    Fantastic article, I’ve never heard of Brutal Doom. Its damage system sounds a bit Dorf-Fortressy, almost.

  12. Kaeoschassis says:

    Sigh. I’m going to have to go play Brutal Doom again, aren’t I?

    I’m going to be honest, I got pretty bored of it pretty quickly. My go-to gameplay mods these days are Demonsteele if I want something completely different, DRLA if I just want a crapload of guns, or Guncaster if I just want pretties, gore, and huge guns. Honestly while Brutal Doom was one of my first Doom mods, and it’s certainly GOOD, it has a lot of little things I really dislike that keeps me shuffling away from it after a few hours. But then I read something like this and inevitably end up firing it up again.

    Since I happen to be reading a Doom article while this is fresh in my head, for a change – a recommendation to my fellow RPS doomers!
    link to forum.zdoom.org

    This is Custom Doom. If you haven’t grabbed it, grab it. It’s tiny, it’s compatible with everything else, and it allows you to fine-tune the difficulty of the game on the fly, whenever. Over the years I’ve found a lot of the more radical gameplay mods make certain mapsets far too easy, or far too difficult. Being able to tweak things like weapon damage and player resistance in real-time make it simple enough to balance anything, for anything, which has me playing modded Doom a lot more than I used to. It actually made Guncaster (semi) balanced, for example.

  13. JoeFX69 says:

    Ive been singing the praises of this mod for ages, its spectacular, and I completely agree with how it is how my nostalgia remembers Doom, and then goes far beyond.

    Unfortunately, the Metal Music Mod I find crap. Andrew Hulshult, who recently worked with that 3d Realms game (lady with tits or whatever) has been steadily re recording all the Doom tracks. This has a similar goal of Brutal Doom, in that the music is what you remember it being like but completely updated at the same time.

    It is the perfect companion for Brutal Doom. Sgt Mark IV even used a track in one of his trailers.

    Check out his Youtube Channel, and download link to moddb.com
    and thank me later

  14. BlacKHeaDSg1 says:

    And yet, this mod works only with one thread (or 1 core) which is stupid. I know that some people are modifying Brutal Doom to work with multi-thread CPU.

    • Phasma Felis says:

      How is that stupid? It’s a bunch of frills on a 23-year-old engine. It shouldn’t need funky multiprocessing tricks.

    • LionsPhil says:

      I’d make a joke about boycotting it until it had 120FPS support, or a Vulkan backend, but…source ports. People actually might.

      • Premium User Badge

        PoulWrist says:

        Doom runs easily at hundreds of frames per second. The game doesn’t tie logic to framerate.

        • LionsPhil says:

          My understanding is that that’s a source port thing: the game’s simulation tickrate is pretty low, so they have to interpolate (else you’d just be rendering identical frames over and over). Dunno if that means they’re introducing a one-tick latency, actually.

  15. Skiv says:

    Today I witnesed a really neat thing. An imp jumped on my head. I swiftly pressed RMB and launched him up in the air with an uppercut. He gibbed due to the sheer force of the blow. *I only want to see you laughing in the ree-eed rain..*

    Next I kicked and imp in the torso. He tumbled backwards. Automatically I shot him with a shotgun. He splatted on the wall.

  16. Ralek says:

    Looks amazing, but whatever happend to Brutal Hexen? I was never much of a Doom guy myself, but Hexen I can digg.

    • Kaeoschassis says:

      While I don’t think there’s been any more development on the original version, another modder has since taken it under his wing and done his own thing with it. Still very much work-in-progress, but you might get some enjoyment out of it if that’s your thing.

      link to forum.zdoom.org