Handle arrow shooting (#101)

[aramperes]

#101

• Handle digging status for using bow
• Find arrow stack and consume in Survival/Adventure
• Submit event for shooting arrow with given position
• Implement Arrow entity
• Spawn Arrow entity with velocity from player's rotation
• Add tests

[codecov]

Codecov Report

Merging #121 into develop will increase coverage by 0.79%.
The diff coverage is 87.03%.

@@             Coverage Diff             @@
##           develop     #121      +/-   ##
===========================================
+ Coverage    57.96%   58.76%   +0.79%     
===========================================
  Files           59       60       +1     
  Lines         8017     8230     +213     
===========================================
+ Hits          4647     4836     +189     
- Misses        3370     3394      +24

Impacted Files	Coverage Δ
server/src/physics/component.rs	95.23% <0%> (+0.11%)	⬆️
core/src/network/packet/implementation.rs	0% <0%> (ø)	⬆️
core/src/entitymeta.rs	0% <0%> (ø)	⬆️
server/src/entity/broadcast.rs	92.96% <100%> (+0.72%)	⬆️
server/src/entity/mod.rs	100% <100%> (ø)	⬆️
server/src/util/mod.rs	86.79% <100%> (+1.07%)	⬆️
server/src/entity/types.rs	76.92% <100%> (+6.92%)	⬆️
server/src/entity/metadata.rs	73.52% <28.57%> (-5.16%)	⬇️
server/src/physics/entity.rs	74.61% <50%> (-2.25%)	⬇️
server/src/entity/arrow.rs	72% <72%> (ø)
... and 4 more

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[caelunshun]

For spawning the arrow, I recommend adding a method to util::Spawner to lazily spawn it, as is done with items. This will avoid the need for tons of component accesses in the player digging system.

[aramperes]

For spawning the arrow, I recommend adding a method to util::Spawner to lazily spawn it, as is done with items. This will avoid the need for tons of component accesses in the player digging system.

Yes, I was thinking of making a PlayerShootBowEvent, with a PlayerShootBowSystem listening for it. The system would then spawn the arrow using a function in Spawner similar to items. Does that seem right?

[caelunshun]

Yes, that seems right. You might want to consider how you could generalize PlayerShootBowEvent to support other arrow shooting causes, such as dispensers.

[caelunshun]

Seems like the velocity is overflowing when being sent to clients.

[caelunshun]

Sorry, accidental close

[aramperes]

So I'm not too sure, but it seems like the scale of velocity is very different for items and arrows. I packet-logged Spigot and saw velocity values in the thousands.

According to https://wiki.vg/Protocol#Entity_Velocity, it should be pretty normal to get very high velocity values since it's measured in 1/8000th of blocks per tick. Why the values are so much smaller for items is unclear to me.

[caelunshun]

The velocity value on Feather is in blocks per tick. The util::protocol_velocity function converts it to the units used for packets, 1/8000 block per tick, which is what you're observing.

[aramperes]

The thing is util::protocol_velocity is performing the opposite conversion: dividing by 8000 is converting the protocol format (short) to blocks-per-tick (float). It should be multiplying the float values by 8000 to convert to short.

[caelunshun]

Ah... so protocol_velocity has always been incorrect, then. It should be multiplying by 8000. Sorry about that.

(Now I know what's causing entities to jitter on the client...)

[aramperes]

I will merge develop into this branch and adjust the velocity.

[aramperes]

Ready for review/merge.

[caelunshun]

Also, physics aren't being applied to arrows on the server side because they don't have a bounding box (EntityPhysicsSystem joins over entities with bounding boxes). This can be observed by shooting an arrow and then rejoining; the arrow will be back to where it was shot from.

[aramperes]

Also, physics aren't being applied to arrows on the server side because they don't have a bounding box (EntityPhysicsSystem joins over entities with bounding boxes). This can be observed by shooting an arrow and then rejoining; the arrow will be back to where it was shot from.

I added a bounding box and made the arrow spawn 1.5 blocks in front of the player. However, it seems like the arrow breaks off its course after a few blocks and falls down. Seems like something is off with the physics impl?

[caelunshun]

Yes, physics::entity::drag_force returns 0 by default, so the velocity gets set to 0. gravitational_accelration should return -0.05 and drag_force 0.99 for arrows. I tried this, and it solved the problem.

[aramperes]

Cool. Is there a value set for the "gliding" effect when the entity is blocked? Arrows should do a full-stop when colliding with a block.

[caelunshun]

That's not implemented yet, but you could just set slip_multiplier to 0.0 for arrows here. https://github.com/caelunshun/feather/blob/d9f973899e74f7816530e50f451da5b7592521a6/server/src/physics/entity.rs#L159

That won't work when the arrow hits a wall—only when it impacts the ground. A more robust solution would be to add an EntityCollideEvent and set arrows' velocities to 0 when the event is triggered. This will require some modification of the physics code, though.

[caelunshun]

Thanks!