Physics-based combat system (resurrect old system?) [$100]

[Cervator]

We had a near-complete combat system done by @aherber back in the legacy days based on a physics model. While we can currently simulate combat by just triggering damage events while two entities are near each other that's pretty boring.

The legacy system had a bow that would shoot different types of arrows including one affected by gravity, one that would bounce off surfaces, etc. It also had a sword for simple melee combat if you were faced with a target you could hit. The next step was enabling positional damage, opening the door to headshots, limb-specific damage, equipment mattering a whole lot more, and whole related systems like armor and health that could be more than just a global pool of points.

Whether we can resurrect the old system or not we need fancier combat!

• @nh-99 made the last attempt to look at it and got it into a branch here in this repo. Note that it is a single commit not isolating the changes, but it should work and somebody should be able to identify the related code and see if it is useful anymore: https://github.com/MovingBlocks/Terasology/tree/combat_archive
• Forum thread: http://forum.terasology.org/threads/combat.420 - lots of details, including near the end a note about @nh-99's work
• Some other basic notes about a simpler system (and old alternative combat) in L&S - Primitive Combat (GelCube style) #603. May not work anymore either.

Somewhat like the Behavior Tree overhaul (#2070) I'm expecting a basic scope here to claim the bounty with lots of bonus potential running into GSOC scale land.

Basic implementation

• Either resurrect the old branch or use it for inspiration to develop a new physics-based combat system. Or surprise us with something clever that gets to the same level of gameplay (more than just mashing buttons in melee hoping you're hitting something). Not expecting where a target is hit to matter here.
• Make a basic projectile weapon that could satisfy Implement a crossbow or similar ranged item #2570 - could be a stepping stone, may not need full physics (more like a tweaked railgun)
• Probably will need to touch on pathfinding or BTs to actually have creatures engage in combat. There are alternative options for AI though
• Implement an aggressive (test) mob that'll use the system with some level of competency (if a player or other suitable target is in range point at it and start shooting it with arrows or what not)
• Allow the player to use the new system as well and aim attacks sensibly. Ideally show a few different projectile types like the old system
• Verify that it all works in multiplayer without atrocious latency :-)
• Add/review javadoc for all involved classes
• Add tutorial about how to work/extend the system and any involved items, again ideally in the style of https://github.com/Terasology/TutorialWorldGeneration/
• Make a showcase video

Advanced implementation

This is far more open-ended and leads into creating/updating related systems

• Improve the display of health and especially the impact from losing/gaining health (combat/healing) - Update basic display of health [$10] #1639
• Make some basic potions that relate to combat. Healing potions, poisons you can apply to a weapon, other weapon enhancement effects (flaming projectiles? A trueshot position making your aim better?) - Module Overhaul - Potions #737
• Implement positional damage. Headshots should hurt more than toeshots. This would then also involve actually defining what's a head and what's a toe.
• Implement an anatomy system that can take the impact from positional damage and give it gameplay value. Could also lead into non-combat factors like hunger, disease, falling, etc. Anatomy System #465
• Make a projectile that can stick to something, be that a wall, a player, or something else. Could also be used for utility like sticky torches - "Sticky" thrown objects (especially torches) #1443
• Make a turret-based weapon that can track specified targets and fire projectiles at them within a certain range and constraints (no firing through walls). Think a guard tower with a balista of some sort. May also relate to Crossbow - L&S II Pawn Storm #664, L&S - Tower turret blocks #591, L&S - Circuitry to help power turrets in towers #589, L&S - "Dice" catapult ammo art assets #581

This issue obsoletes #590 - figured I'd create a new one to get it fully up to speed.

[0shine0]

Pinging @Cervator to discuss its potential in Gsoc and also about its implementation.

I am thinking about using the useful parts from the old branch to facilitate a new combat system. Should I make the system in a new module or make it in core module?

[portokaliu]

Scavenging bits of the old system was always an idea, since the functionality seemed to be there. The only issue was that it used a really old version of the game and rooted itself in some core/engine classes, when it would most likely need to be a module.

[0shine0]

@portokaliu I am also thinking about introducing a density property for non-solid materials like water. To affect speed and motion of a projectile in water as compared to when in air.
Is it feasible performance wise?

[portokaliu]

@0shine0 This was one of the ideas for the movement refactoring, but that only referred to the player. Suffice to say, I'm not against that concept

[0shine0]

@portokaliu alright, gonna try that with combat system.

[Cervator]

Closing this as completed as part of GSOC 2017, woo! New module https://github.com/Terasology/CombatSystem is the primary home for the new system, and has some sibling modules :-)

Thanks @0shine0 and mentors @portokaliu @niksoc @xrtariq2594 !

As usual there are plenty of additional areas that could still be worked on, maybe especially positional combat / damage, but that is for another day :-)

For a summary of work done see https://gist.github.com/0shine0/aba355bbc437b57b3c5d8aaeaa2a0296

Also, somebody should claim the bounty on top :D