You assume the role of team leader in the tactical response team of a major city police force. Your work is to plan and carry out tactical entry in barricade and hostage situations with the least possible loss of life as the desired outcome.

Blood & Bullet is a side-scroller that strives to provide a realistic model for projectile interactions and injuries. Once someone is hurt the player will be working against the clock. Gear and tactics must be chosen carefully to limit collateral damage and minimize resistance.

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Character physiology in Blood & Bullet

I want a couple of key features in Blood & Bullet to be realistic. One of those are how characters are injured and what the effects of the injuries are. I am by no means an expert but I use the knowledge I have and what I'm able to find. Since the characters in my game are 2-dimensional I have to play some tricks to simulate the third and missing dimension.

The characters' bodies are composed of limbs, and to each limb I can attach what I call vital properties. When a limb is hit by a projectile I randomize which of the vital properties are hit based on probabilities for each of the properties. For instance hitting the spine inside the torso has a much lower probability than hitting the lungs, since the lungs cover a larger volume of the torso than the spine does.

Some of the vitals I can add to limbs are as follows.

Locomotive bones
These are bones that are necessary for the character to move. When these are damaged the character will start to limp and if the impact is powerful enough it will knock the character off its feet. This is used in all the limbs from the feet up to the pelvis.

Major blood vessels
If these are hit the limb will bleed at its maximum rate. Depending on which limb it is it may cause the character to bleed out and loose consciousness very quickly.

When the lungs are hit their capacity to store oxygen is reduced.

When the heart is hit it will function less efficiently and skip beats or stop completely. The amount of oxygen transferred to the blood is reduced.

When the spine is hit I want to turn off motor control to the limbs below the hit region but I can't do that yet. Now the character simply falls to the ground.

When the brain is even slightly damaged the character loses consciousness. Further it is divided into a couple of parts making it possible for the character to lose:

  • Circulation control - the heart stops
  • Respiration (breathing) control - respiration stops
  • Motor control - muscles in limbs cramp or spasm

What it takes to stay alive

For a character to remain alive in Blood & Bullet its brain must be intact and supplied with oxygen. That is the only criteria. If the brain is too damaged the character dies. The brain receives damage both from trauma (projectile hits) and over time by lack of oxygen. The brain can be without oxygen for 30 seconds before it dies. That value is game-ified of course and it will probably be different depending on the level of difficulty selected.

For the brain to be supplied with sufficient oxygen both the character's respiration and circulation must function properly, meaning it needs to breath and the heart needs to beat. As you saw above, both of these can be impaired by trauma from being shot, or disabled completely if the brain is hit. The character is unable to remain conscious when the oxygen level becomes low and this happens long before brain death, so a character lying on the ground in Blood & Bullet is usually just unconscious and not dead.

Work intensity

On the characters I have a value that represents how hard they are working themselves physically. It becomes high when they are running and it's low when they are standing still, but everything they do takes work. Even breathing and pumping the heart takes some work.

This is the basis of the physiology in B&B:

  1. A character breathes and pumps blood to provide itself with oxygen.
  2. The level of work a character does directly affects how much oxygen is taken from its blood.
  3. When the amount of oxygen in a character's blood becomes low, its heart compensates by pumping faster. This removes oxygen from its lungs faster but provides more oxygen.
  4. When the amount of oxygen produced by a character's breathing becomes insufficient the character compensates by breathing faster.

This all fits together rather neatly. While tweaking it I was pleasantly surprised when I managed to strain the player character so hard by running that he lost consciousness!

WalkingPulse during walk

Above: Pulse, blood pressure, respiration and work intensity during a walk.

RunningPulse during run

The same values some time into a sprint. Note that also the blood pressure is higher during work because it must circulate faster. Diastolic pressure is the lowest pressure during the beat cycle that occurs while the heart muscle is relaxed.

How it affects gameplay

Now that you understand that the characters in Blood & Bullet have "real" pulses you can see that a character that has been working hard will bleed out faster than a character that was resting if they were injured, because the heart pumps the blood out of the wound faster.

You can see that stabilizing a downed suspect to make him bleed slower may buy you time to finish the mission before he dies. (Proper healthcare cannot be provided before you have secured the building.)

You can also see that it's equally important that you make sure unconscious characters don't suffocate from having their breathing obstructed.

You will have the option to equip your team members with medical kits that can stop or slow down bleeding. It will be up to you to decide when to use them. Some missions may be so time critical that you simply don't have the time to stop before you have cleared the whole building.

It is my hope that this adds to the gameplay and that it puts the use of force into some perspective. At least for the campaign missions. The sandbox mode is quite different in how it is played but the same character physiology is in place there as well.

Thanks for reading!

Behavior of occupants in Blood & Bullet

Behavior of occupants in Blood & Bullet

News 6 comments

I go through a bit of the current artificial intelligence in Blood & Bullet, implemented with behavior trees. Skip to the end for lots of animations.

Realistic ballistics in Blood & Bullet

Realistic ballistics in Blood & Bullet

News 7 comments

I go through parts of the fairly sophisticated ballistics model in Blood & Bullet.

What happens next?

What happens next?

News 3 comments

It's been a long time coming. I'm now looking into a new way of developing Blood & Bullet. All in order to make more efficient use of my time.

Signs of progress

Signs of progress

News 5 comments

I've been working in the quiet lately but it's time I posted a new update.

Real Gun Sounds

Real Gun Sounds

Other 4 comments


Release 1

Release 1

Enhanced Bodies Demo 0 comments

First release / possible demo / full release of the addon. Tip: Backup your hostage files before installing. To do that, go to "bloodandbullet/data/graphics/bodies...

Demo 3

Demo 3

Demo 30 comments

The third Blood and Bullet demo adds more game play mechanics. Use concussion grenades to overwhelm the suspects. Restrain them, secure their weapons...

Demo 2

Demo 2

Demo 2 comments

This demo is more of a taste of game play than the previous one, but still with some obvious parts missing. There are more weapons, a bit of AI, rooms...

Sandbox/tech demo

Sandbox/tech demo

Demo 4 comments

This is not a game-play demo. I just want to point that out. It's a sandbox/tech demo of the features so far. It's scaled down a bit to keep it simple...

Comments  (0 - 10 of 281)

And yeah, can you pleeeeaaase release any of the latest builds on old engine somehow? I'd (and not only me i think) really like to see them.

It would be really interesting to check it (or them) out not only to see how your ideas progressed but to see the engine itself. I mean, dude, you have built it from scratch!

I would sincerely appreciate if you do.

I dream about it literally every few days.

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Nice idea ! Sniper mode...:P

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isbeorn Creator

I actually tried it yesterday, I found a state in the version history where the sniper mode was working. But I had problems compiling it in release mode. So I didn't quite make it all the way. Maybe I can finish it next time I have some spare time.

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That's actually some great news! At least we've got yourselves some hope now.

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rlly ? That's sad :d

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Maybe as a bonus for the unity realese? Idk just by any possible reason.


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isbeorn Creator

I'm sorry I just can't do that. It would take too much work. But you will get to enjoy the Unity version soon. It builds on everything I learned from making the previous versions and it's much better in every way!

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But why? I understand that if its too much work it won't be worth it... But I also thought that you had a working build and just didn't want to give it to us cause it wasn't finished.
I mean, you didn't completely delete it, right? So maybe there's a slim chance that it will happen?
Again, I understand that if you have to restore it somehow in order to get it working or smth. But if its not the case why not?

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isbeorn Creator

Yeah that's the thing it's not in a working state. There might be some state in the version history that is restorable with some work, but honestly to me it's not worth it. The work of finding that version state, and then the work of restoring it is time I want to spend on moving forward with the current game. Thanks for understanding!

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Latest tweets from @bloodandbullet

I'm doing other stuff this week so there won't be many updates.

May 24 2016

I've done some really neat stuff on how the computer characters perceive audio today. Playing stealth is becoming viable.

May 22 2016

Today I'll finish mission objectives fulfillment (with UI indications), and ending the mission by returning to the exit.

May 20 2016

This animation stuff I've been working on is too complicated. I'll have to postpone it to after the sandbox.

May 19 2016

Tricky animation stuff today, I have some problems that need to be solved.

May 19 2016

I'm working on whole body animations. They will be used for characters without weapons, so that they can do stuff with their arms.

May 18 2016

It's been a few days. I've done level design and I've got reflection mapping working. It really does wonders for the blood puddles!

May 17 2016

I'm away from home over the weekend so there'll be no work on the code. But I will record lots of audio!

May 12 2016

I'm adding user interface for managing the bullet time settings from the in-mission menu.

May 11 2016

I'm recording some audio today. I've no idea if it'll turn into something usable.

May 8 2016

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