<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 bounce off projectiles from surfaces. For this to be triggered, your entity must be the one that's colliding, have some velocity <page>ENTITY:SetMoveType</page> must either be `MOVETYPE_FLY` or `MOVETYPE_FLY_GRAVITY` and <page>ENTITY:SetMoveCollide</page> must be `MOVECOLLIDE_FLY_CUSTOM`. <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> </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 function ENT:ResolveCustomFlyCollision(traceResult, vel) vel = self:GetVelocity() -- use unmodified velocity local normal = vel - 2 * vel:Dot(traceResult.HitNormal) * traceResult.HitNormal local speed = vel:Length() normal = normal:GetNormalized() self:SetLocalVelocity(normal * speed) self:SetAngles(normal:Angle()) end </code> </example>