Fix projectiles not inheriting velocities from the shooter/gun. (#12854)

Fixes https://github.com/space-wizards/space-station-14/issues/12852

Content.Client/Weapons/Ranged/Systems/GunSystem.cs

@@ -158,18 +158,8 @@ public sealed partial class GunSystem : SharedGunSystem
             return;
         }
 
-        EntityCoordinates coordinates;
+        // Define target coordinates relative to gun entity, so that network latency on moving grids doesn't fuck up the target location.
-
+        var coordinates = EntityCoordinates.FromMap(entity, mousePos, EntityManager);
-        // Bro why would I want a ternary here
-        // ReSharper disable once ConvertIfStatementToConditionalTernaryExpression
-        if (MapManager.TryFindGridAt(mousePos, out var grid))
-        {
-            coordinates = EntityCoordinates.FromMap(grid.GridEntityId, mousePos, EntityManager);
-        }
-        else
-        {
-            coordinates = EntityCoordinates.FromMap(MapManager.GetMapEntityId(mousePos.MapId), mousePos, EntityManager);
-        }
 
         Sawmill.Debug($"Sending shoot request tick {Timing.CurTick} / {Timing.CurTime}");
 

Content.Server/Magic/MagicSystem.cs

@@ -1,4 +1,4 @@
-using System.Threading;
+using System.Threading;
 using Content.Server.Body.Components;
 using Content.Server.Body.Systems;
 using Content.Server.Coordinates.Helpers;
@@ -16,6 +16,7 @@ using Content.Shared.Maps;
 using Content.Shared.Physics;
 using Content.Shared.Spawners.Components;
 using Content.Shared.Storage;
+using Robust.Server.GameObjects;
 using Robust.Shared.Audio;
 using Robust.Shared.Map;
 using Robust.Shared.Physics.Components;
@@ -39,7 +40,9 @@ public sealed class MagicSystem : EntitySystem
     [Dependency] private readonly SharedActionsSystem _actionsSystem = default!;
     [Dependency] private readonly DoAfterSystem _doAfter = default!;
     [Dependency] private readonly GunSystem _gunSystem = default!;
+    [Dependency] private readonly PhysicsSystem _physics = default!;
     [Dependency] private readonly SharedTransformSystem _transformSystem = default!;
+
     public override void Initialize()
     {
         base.Initialize();
@@ -155,11 +158,18 @@ public sealed class MagicSystem : EntitySystem
             return;
 
         var xform = Transform(ev.Performer);
+        var userVelocity = _physics.GetMapLinearVelocity(ev.Performer);
 
         foreach (var pos in GetSpawnPositions(xform, ev.Pos))
         {
-            var ent = Spawn(ev.Prototype, pos.SnapToGrid(EntityManager, _mapManager));
+            // If applicable, this ensures the projectile is parented to grid on spawn, instead of the map.
-            _gunSystem.ShootProjectile(ent, ev.Target.Position - Transform(ent).Coordinates.Position, ev.Performer);
+            var mapPos = pos.ToMap(EntityManager);
+            EntityCoordinates spawnCoords = _mapManager.TryFindGridAt(mapPos, out var grid)
+                ? pos.WithEntityId(grid.Owner, EntityManager)
+                : new(_mapManager.GetMapEntityId(mapPos.MapId), mapPos.Position);
+
+            var ent = Spawn(ev.Prototype, spawnCoords);
+            _gunSystem.ShootProjectile(ent, ev.Target.Position - mapPos.Position, userVelocity, ev.Performer);
         }
     }
 

Content.Server/Weapons/Ranged/Systems/GunSystem.cs

@@ -92,10 +92,15 @@ public sealed partial class GunSystem : SharedGunSystem
         var mapAngle = mapDirection.ToAngle();
         var angle = GetRecoilAngle(Timing.CurTime, gun, mapDirection.ToAngle());
 
+        // If applicable, this ensures the projectile is parented to grid on spawn, instead of the map.
+        EntityCoordinates fromEnt = MapManager.TryFindGridAt(fromMap, out var grid)
+            ? fromCoordinates.WithEntityId(grid.Owner, EntityManager)
+            : new(MapManager.GetMapEntityId(fromMap.MapId), fromMap.Position);
+
         // Update shot based on the recoil
         toMap = fromMap.Position + angle.ToVec() * mapDirection.Length;
         mapDirection = toMap - fromMap.Position;
-        var entityDirection = Transform(fromCoordinates.EntityId).InvWorldMatrix.Transform(toMap) - fromCoordinates.Position;
+        var gunVelocity = Physics.GetMapLinearVelocity(gun.Owner);
 
         // I must be high because this was getting tripped even when true.
         // DebugTools.Assert(direction != Vector2.Zero);
@@ -116,15 +121,15 @@ public sealed partial class GunSystem : SharedGunSystem
 
                             for (var i = 0; i < cartridge.Count; i++)
                             {
-                                var uid = Spawn(cartridge.Prototype, fromMap);
+                                var uid = Spawn(cartridge.Prototype, fromEnt);
-                                ShootProjectile(uid, angles[i].ToVec(), user, gun.ProjectileSpeed);
+                                ShootProjectile(uid, angles[i].ToVec(), gunVelocity, user, gun.ProjectileSpeed);
                                 shotProjectiles.Add(uid);
                             }
                         }
                         else
                         {
-                            var uid = Spawn(cartridge.Prototype, fromMap);
+                            var uid = Spawn(cartridge.Prototype, fromEnt);
-                            ShootProjectile(uid, mapDirection, user, gun.ProjectileSpeed);
+                            ShootProjectile(uid, mapDirection, gunVelocity, user, gun.ProjectileSpeed);
                             shotProjectiles.Add(uid);
                         }
 
@@ -167,7 +172,7 @@ public sealed partial class GunSystem : SharedGunSystem
                         break;
                     }
 
-                    ShootProjectile(newAmmo.Owner, mapDirection, user, gun.ProjectileSpeed);
+                    ShootProjectile(newAmmo.Owner, mapDirection, gunVelocity, user, gun.ProjectileSpeed);
                     break;
                 case HitscanPrototype hitscan:
                     var ray = new CollisionRay(fromMap.Position, mapDirection.Normalized, hitscan.CollisionMask);
@@ -229,11 +234,15 @@ public sealed partial class GunSystem : SharedGunSystem
         }, false);
     }
 
-    public void ShootProjectile(EntityUid uid, Vector2 direction, EntityUid? user = null, float speed = 20f)
+    public void ShootProjectile(EntityUid uid, Vector2 direction, Vector2 gunVelocity, EntityUid? user = null, float speed = 20f)
     {
         var physics = EnsureComp<PhysicsComponent>(uid);
         physics.BodyStatus = BodyStatus.InAir;
-        Physics.SetLinearVelocity(physics, direction.Normalized * speed);
+
+        var targetMapVelocity = gunVelocity + direction.Normalized * speed;
+        var currentMapVelocity = Physics.GetMapLinearVelocity(uid, physics);
+        var finalLinear = physics.LinearVelocity + targetMapVelocity - currentMapVelocity;
+        Physics.SetLinearVelocity(physics, finalLinear);
 
         if (user != null)
         {