Particle additions:

- Support for subemitters (= particles can emit particles).
- Option to set a different velocity change value for particles in water (can be used to simulate buouancy).
- Fixed drag vector & timer not being reset when initializing a particle.

Barotrauma/BarotraumaClient/Source/Particles/ParticlePrefab.cs

@@ -101,6 +101,20 @@ namespace Barotrauma.Particles
             }
         }
 
+        private Vector2 velocityChangeWater;
+        public Vector2 VelocityChangeWaterDisplay { get; private set; }
+
+        [Editable(ToolTip = "How much the velocity of the particle changes per second when in water."), Serialize("0.0,0.0", false)]
+        public Vector2 VelocityChangeWater
+        {
+            get { return velocityChangeWater; }
+            private set
+            {
+                velocityChangeWater = value;
+                VelocityChangeWaterDisplay = ConvertUnits.ToDisplayUnits(value);
+            }
+        }
+
         [Editable(0.0f, 10000.0f, ToolTip = "Drag applied to the particle when it's moving through water."), Serialize(0.0f, false)]
         public float CollisionRadius { get; private set; }
 
@@ -164,6 +178,8 @@ namespace Barotrauma.Particles
 
         //----------------------------------------------------
 
+        public readonly List<ParticleEmitterPrefab> SubEmitters = new List<ParticleEmitterPrefab>();
+
         public Dictionary<string, SerializableProperty> SerializableProperties
         {
             get;
@@ -191,9 +207,20 @@ namespace Barotrauma.Particles
                     case "animatedsprite":
                         Sprites.Add(new SpriteSheet(subElement));
                         break;
+                    case "particleemitter":
+                    case "emitter":
+                    case "subemitter":
+                        SubEmitters.Add(new ParticleEmitterPrefab(subElement));
+                        break;
                 }
             }
 
+            //if velocity change in water is not given, it defaults to the normal velocity change
+            if (element.Attribute("velocitychangewater") == null)
+            {
+                VelocityChangeWater = VelocityChange;
+            }
+
             if (element.Attribute("angularvelocity") != null)
             {
                 AngularVelocityMin = element.GetAttributeFloat("angularvelocity", 0.0f);