<function name="ResolveCustomFlyCollision" parent="ENTITY" type="hook"> <added>2026.04.08</added> <description>Called during a non-VPhysics collision event for flying entities. This is best used to make projectiles bounce off from surfaces in their own way. For this to be triggered, this entity must be the one that's colliding, have some velocity, <page>Entity:GetMoveType</page> must be either <page text="MOVETYPE_FLY">Enums/MOVETYPE#MOVETYPE_FLY</page> or <page text="MOVETYPE_FLYGRAVITY">Enums/MOVETYPE#MOVETYPE_FLYGRAVITY</page>, and <page>Entity:GetMoveCollide</page> must be <page text="MOVECOLLIDE_FLY_CUSTOM">Enums/MOVECOLLIDE#MOVECOLLIDE_FLY_CUSTOM</page>. <note>This works only on `anim` type entities.</note></description> <realm>Server</realm> <args> <arg name="traceResult" type="table{TraceResult}">The <page>Structures/TraceResult</page> where the collision occured.</arg> <arg name="vel" type="vector">The calculated velocity after calculations such as bounciness, elasticity, ground sliding etc...</arg> </args> <rets> <ret type="boolean">Return `true` to prevent default action.</ret> </rets> </function> <example> <description>A rocket model which directly reflects off from surfaces without any velocity loss, similar to `sent_ball`.</description> <code> AddCSLuaFile() ENT.Base = "base_anim" ENT.Type = "anim" ENT.PrintName = "Bouncy Rocket" ENT.Category = "Other" ENT.Editable = true ENT.Spawnable = true ENT.AdminOnly = true ENT.RenderGroup = RENDERGROUP_TRANSLUCENT ENT.PhysicsSolidMask = MASK_SOLID + CONTENTS_HITBOX -- collide with vphysics function ENT:Initialize() self:SetModel( "models/weapons/w_missile_closed.mdl" ) self:SetMoveType( MOVETYPE_FLY ) self:SetMoveCollide( MOVECOLLIDE_FLY_CUSTOM ) self:SetCollisionGroup( COLLISION_GROUP_PROJECTILE ) self:SetSolid( SOLID_BBOX ) -- turns on collision with other entities self:SetCollisionBounds( Vector( -1, -1, -1 ), Vector( 1, 1, 1 ) ) self:SetVelocity( self:GetForward() * 650 ) end ⤶ if ( CLIENT ) then return end⤶ function ENT:ResolveCustomFlyCollision( traceResult, vel ) vel = self:GetVelocity() -- using unmodified velocity local speed = vel:Length() local tempdir = traceResult.HitNormal tempdir:Mul( 2 * vel:Dot( tempdir ) ) local dir = vel dir:Sub( tempdir ) dir:Normalize() local reflectionangle = dir:Angle() local newvel = dir newvel:Mul( speed ) self:SetLocalVelocity( newvel ) self:SetAngles( reflectionangle ) end </code> </example> <example> <description>A reduced version of the engine's crossbow bolt that replicates the behavior closely. It flies. It reflects. It sticks. It hurts.</description> <code> AddCSLuaFile() ENT.Base = "base_anim" ENT.Type = "anim" ENT.PrintName = "Simple Crossbow Bolt" ENT.Category = "Other" ENT.Spawnable = true ENT.AdminOnly = true ENT.RenderGroup = RENDERGROUP_OPAQUE ENT.PhysicsSolidMask = bit.band( bit.bor( MASK_SOLID, CONTENTS_HITBOX ), bit.bnot( CONTENTS_GRATE ) ) function ENT:Initialize() self:SetModel( "models/crossbow_bolt.mdl" ) self:SetSolid( SOLID_BBOX ) self:AddSolidFlags( FSOLID_NOT_STANDABLE ) self:SetCollisionGroup( COLLISION_GROUP_PROJECTILE ) self:SetCollisionBounds( Vector( -1, -1, -1 ), Vector( 1, 1, 1 ) ) self:SetMoveType( MOVETYPE_FLYGRAVITY ) self:SetMoveCollide( MOVECOLLIDE_FLY_CUSTOM ) self:SetGravity( 0.05 ) self:SetSkin( 1 ) end if ( CLIENT ) then return end local BOLT_AIR_VELOCITY = 3500 function ENT:SpawnFunction( pPlayer, trace_t, classname ) if ( not trace_t.Hit ) then return end local aimdirection = trace_t.Normal local angles = aimdirection:Angle() local origin local velocity local simplecrossbowbolt = ents.Create( classname ) simplecrossbowbolt:SetAngles( angles ) origin = aimdirection origin:Mul( 32 ) origin:Add( trace_t.StartPos ) simplecrossbowbolt:SetPos( origin ) velocity = origin velocity:Sub( trace_t.StartPos ) velocity:Div( 32 ) velocity:Mul( BOLT_AIR_VELOCITY ) simplecrossbowbolt:SetVelocity( velocity ) simplecrossbowbolt:SetOwner( pPlayer ) simplecrossbowbolt:Spawn() return simplecrossbowbolt end function ENT:ResolveCustomFlyCollision( trace_t, velocity ) if ( trace_t.HitSky ) then return self:Remove() end local pOther = trace_t.Entity self:EmitSound( "Weapon_Crossbow.BoltHitWorld" ) local direction = self:GetVelocity() local speed = direction:Length() direction:Normalize() direction:Negate() local hitDot = trace_t.HitNormal:Dot( direction ) direction:Negate() if ( ( hitDot < 0.5 ) and ( speed > 100 ) ) then -- Reflect off local vecReflection = Vector( 0, 0, 0 ) vecReflection:Set( trace_t.HitNormal ) vecReflection:Mul( 2 * hitDot ) vecReflection:Add( direction ) self:SetAngles( vecReflection:Angle() ) velocity = vecReflection velocity:Mul( speed * 0.75 ) self:SetLocalVelocity( velocity ) self:SetGravity( 1 ) else -- Stick ⤶ self:SetMoveType( MOVETYPE_NONE )⤶ self:SetCollisionGroup( COLLISION_GROUP_DEBRIS )⤶ ⤶ self:SetSkin( 0 )⤶ -- Move the bolt back a bit so it looks clean local compensatedpos = Vector( 0, 0, 0 ) compensatedpos:Set( trace_t.Normal ) compensatedpos:Mul( -6 ) compensatedpos:Add( trace_t.HitPos ) ⤶ self:SetPos( compensatedpos )⤶ -- Make it stick self:SetMoveType( MOVETYPE_NONE )⤶ self:SetPos( compensatedpos )⤶ self:SetParent( pOther ) self:SetSkin( 0 )⤶ -- Leave an impact effect local data = EffectData() data:SetOrigin( trace_t.HitPos ) data:SetStart( trace_t.StartPos ) data:SetSurfaceProp( trace_t.SurfaceProps ) data:SetDamageType( DMG_BULLET ) data:SetHitBox( trace_t.HitBox ) data:SetEntIndex( pOther:EntIndex() ) util.Effect( "Impact", data ) -- Cause some damage local info = DamageInfo() info:SetAttacker( self:GetOwner() ) info:SetInflictor( self ) info:SetDamage( 20 ) info:SetDamage( 100 ) info:SetDamageType( DMG_BULLET ) info:SetDamagePosition( trace_t.HitPos ) local force = compensatedpos force:Set( trace_t.Normal ) force:Mul( 75 * 4 ) force:Mul( 75 * 4 * 0.7 ) info:SetDamageForce( force ) pOther:TakeDamageInfo( info ) -- Schedule removal self.Think = self.Remove self:NextThink( CurTime() + 10 ) end -- Shoot sparks local data = EffectData() data:SetOrigin( trace_t.HitPos ) data:SetMagnitude( 1 ) data:SetMagnitude( 2 ) data:SetScale( 1 ) data:SetNormal( trace_t.HitNormal )⤶ data:SetRadius( 1 ) util.Effect( "Sparks", data ) local normal = trace_t.Normal⤶ normal:Negate() data:SetNormal( normal ) util.Effect( "ElectricSpark", data )⤶ end </code> </example>