How to make a trail follow a thrown prop

[Lord_Melvin]

So i'm making a SWEP that throws a prop, but I want a trail to follow it once it's thrown. How do I do that?

Here is my code:

SWEP.Author			= "Lord_Melvin" -- These two options will be shown when you have the weapon highlighted in the weapon selection menu
SWEP.Instructions		= "fires a regular punch"

SWEP.Spawnable = true
SWEP.AdminOnly = false

SWEP.Category				= "One Piece"
SWEP.Primary.ClipSize		= -1
SWEP.Primary.DefaultClip	= -1
SWEP.Primary.Automatic		= false
SWEP.Primary.Ammo		= "none"



SWEP.Secondary.ClipSize		= -1
SWEP.Secondary.DefaultClip	= -1
SWEP.Secondary.Automatic	= false
SWEP.Secondary.Ammo		= "none"
SWEP.Weight			= 5
SWEP.AutoSwitchTo		= false
SWEP.AutoSwitchFrom		= false

SWEP.Slot			= 1
SWEP.SlotPos			= 2
SWEP.DrawAmmo			= false
SWEP.DrawCrosshair		= true




SWEP.ViewModel			= "models/weapons/v_smg1.mdl"
SWEP.WorldModel			= "models/weapons/w_smg1.mdl"

local ShootSound = "weapons/one piece/fist/pistal.mp3"
local DeploySound = "weapons/one piece/fist/gomu gomu no.mp3"

function SWEP:Deploy()
		self:EmitSound( DeploySound )
end

function SWEP:PrimaryAttack()

	self.Weapon:SetNextPrimaryFire( CurTime() + 0.1 )


	self:ThrowChair( "models/props/luffy/fist/fist.mdl" )
	
	

end

--
-- Called when the rightmouse button is pressed
--
function SWEP:SecondaryAttack()

	-- Note we don't call SetNextSecondaryFire here because it's not
	-- automatic and so we let them fire as fast as they can click.

	-- Call 'ThrowChair' on self with this model
	self:ThrowChair( "models/props/luffy/fist/fist.mdl" )


end

--
-- A custom function we added. When you call this the player will fire a chair!
--
function SWEP:ThrowChair( model_file )

	--
	-- Play the shoot sound we precached earlier!
	--
	self:EmitSound( ShootSound )


	--
	-- If we're the client then this is as much as we want to do.
	-- We play the sound above on the client due to prediction.
	-- ( if we didn't they would feel a ping delay during multiplayer )
	--
	if ( CLIENT ) then return end

	--
	-- Create a prop_physics entity
	--
	local ent = ents.Create( "prop_physics" )

	--
	-- Always make sure that created entities are actually created!
	--
	if ( !IsValid( ent ) ) then return end

	--
	-- Set the entity's model to the passed in model
	--
	ent:SetModel( model_file )

	--
	-- Set the position to the player's eye position plus 16 units forward.
	-- Set the angles to the player'e eye angles. Then spawn it.
	--
	ent:SetPos( self.Owner:EyePos() + ( self.Owner:GetAimVector() * 16 ) )
	ent:SetAngles( self.Owner:EyeAngles() )
	ent:Spawn()


	--
	-- Now get the physics object. Whenever we get a physics object
	-- we need to test to make sure its valid before using it.
	-- If it isn't then we'll remove the entity.
	--
	local phys = ent:GetPhysicsObject()
	if ( !IsValid( phys ) ) then ent:Remove() return end


	--
	-- Now we apply the force - so the chair actually throws instead
	-- of just falling to the ground. You can play with this value here
	-- to adjust how fast we throw it.
	--
	local velocity = self.Owner:GetAimVector()
	velocity = velocity * 10000
	velocity = velocity + ( VectorRand() * 1000 ) -- a random element
	phys:ApplyForceCenter( velocity )
	
	
	timer.Simple(2.5, function()
	if ent:IsValid() then ent:Remove() end
	end)
	--
	-- Assuming we're playing in Sandbox mode we want to add this
	-- entity to the cleanup and undo lists. This is done like so.
	--
	cleanup.Add( self.Owner, "props", ent )

	undo.Create( "Thrown_punch" )
		undo.AddEntity( ent )
		undo.SetPlayer( self.Owner )
	undo.Finish()
end

[c👌de_g🎷]

Run this on the entity once you spawn it serverside: [url]https://wiki.garrysmod.com/page/util/SpriteTrail[/url]

Make sure you store the return value to a variable, so if you undo the prop you can remove the trail as well.

[Lord_Melvin]

I'm getting some errors, I also want to know if I need a string texture and were do I find my ent?

function SWEP:ThrowChair( model_file )

	--
	-- Play the shoot sound we precached earlier!
	--
	self:EmitSound( ShootSound )


	--
	-- If we're the client then this is as much as we want to do.
	-- We play the sound above on the client due to prediction.
	-- ( if we didn't they would feel a ping delay during multiplayer )
	
	
	
	--
	if ( CLIENT ) then return end

	--
	-- Create a prop_physics entity
	--
	local ent = ents.Create( "prop_physics" )

	--
	-- Always make sure that created entities are actually created!
	--
	if ( !IsValid( ent ) ) then return end

	--
	-- Set the entity's model to the passed in model
	--
	
	util.SpriteTrail( ent,0,Color(255,163,128,255) ,true, 100, 100, 2.5, 0.0025)

	
	ent:SetModel( model_file )

	--
	-- Set the position to the player's eye position plus 16 units forward.
	-- Set the angles to the player'e eye angles. Then spawn it.
	--
	ent:SetPos( self.Owner:EyePos() + ( self.Owner:GetAimVector() * 16 ) )
	ent:SetAngles( self.Owner:EyeAngles() )
	ent:Spawn()


	--
	-- Now get the physics object. Whenever we get a physics object
	-- we need to test to make sure its valid before using it.
	-- If it isn't then we'll remove the entity.
	--
	local phys = ent:GetPhysicsObject()
	if ( !IsValid( phys ) ) then ent:Remove() return end


	--
	-- Now we apply the force - so the chair actually throws instead
	-- of just falling to the ground. You can play with this value here
	-- to adjust how fast we throw it.
	--
	local velocity = self.Owner:GetAimVector()
	velocity = velocity * 10000
	velocity = velocity + ( VectorRand() * 1000 ) -- a random element
	phys:ApplyForceCenter( velocity )
	
	
	timer.Simple(2.5, function()
	if ent:IsValid() then ent:Remove() end
	end)
	--
	-- Assuming we're playing in Sandbox mode we want to add this
	-- entity to the cleanup and undo lists. This is done like so.
	--
	cleanup.Add( self.Owner, "props", ent )

	undo.Create( "Thrown_punch" )
		undo.AddEntity( ent )
		undo.SetPlayer( self.Owner )
	undo.Finish()
end

[editline]12th May 2016[/editline]

Error:

[ERROR] addons/one piece swep/lua/weapons/weapon_punch/shared.lua:101: bad argument #9 to 'SpriteTrail' (string expected, got no value)
1. SpriteTrail - [C]:-1
2. ThrowChair - addons/one piece swep/lua/weapons/weapon_punch/shared.lua:101
3. unknown - addons/one piece swep/lua/weapons/weapon_punch/shared.lua:46

[Lord_Melvin]

Ok I switched the ent and I got this error

[ERROR] addons/one piece swep/lua/weapons/weapon_punch/shared.lua:101: Tried to use a NULL entity!
1. SpriteTrail - [C]:-1
2. ThrowChair - addons/one piece swep/lua/weapons/weapon_punch/shared.lua:101
3. unknown - addons/one piece swep/lua/weapons/weapon_punch/shared.lua:46

Code:

function SWEP:ThrowChair( model_file )

	--
	-- Play the shoot sound we precached earlier!
	--
	self:EmitSound( ShootSound )


	--
	-- If we're the client then this is as much as we want to do.
	-- We play the sound above on the client due to prediction.
	-- ( if we didn't they would feel a ping delay during multiplayer )
	
	
	
	--
	if ( CLIENT ) then return end

	--
	-- Create a prop_physics entity
	--
	local ent = ents.Create( "prop_physics" )

	--
	-- Always make sure that created entities are actually created!
	--
	if ( !IsValid( ent ) ) then return end

	--
	-- Set the entity's model to the passed in model
	--
	
	util.SpriteTrail( ThrowChair,0,Color(255,163,128,255) ,true, 100, 100, 2.5, 0.0025)

	
	ent:SetModel( model_file )

	--
	-- Set the position to the player's eye position plus 16 units forward.
	-- Set the angles to the player'e eye angles. Then spawn it.
	--
	ent:SetPos( self.Owner:EyePos() + ( self.Owner:GetAimVector() * 16 ) )
	ent:SetAngles( self.Owner:EyeAngles() )
	ent:Spawn()


	--
	-- Now get the physics object. Whenever we get a physics object
	-- we need to test to make sure its valid before using it.
	-- If it isn't then we'll remove the entity.
	--
	local phys = ent:GetPhysicsObject()
	if ( !IsValid( phys ) ) then ent:Remove() return end


	--
	-- Now we apply the force - so the chair actually throws instead
	-- of just falling to the ground. You can play with this value here
	-- to adjust how fast we throw it.
	--
	local velocity = self.Owner:GetAimVector()
	velocity = velocity * 100000
	velocity = velocity + ( VectorRand() * 1000 ) -- a random element
	phys:ApplyForceCenter( velocity )
	
	
	timer.Simple(2.5, function()
	if ent:IsValid() then ent:Remove() end
	end)
	--
	-- Assuming we're playing in Sandbox mode we want to add this
	-- entity to the cleanup and undo lists. This is done like so.
	--
	cleanup.Add( self.Owner, "props", ent )

	undo.Create( "Thrown_punch" )
		undo.AddEntity( ent )
		undo.SetPlayer( self.Owner )
	undo.Finish()
end

[McDunkinY]

Well, obviously it's a null entity, nowhere in the code do I see another instance of "ThrowChair" as an entity...

If you take a close look at the wiki, it says its first argument is an entity and ThrowChair isn't an entity, it's a method of "SWEP". Replace "ThrowChair" with "ent" which is the entity the SWEP creates. Finally, as previously mentioned: [QUOTE]Make sure you store the return value to a variable, so if you undo the prop you can remove the trail as well.[/QUOTE]

Make a reference to the return value of util.SpriteTrail, which is another entity, so that you may remove it when the thrown entity is removed, or manipulate it after it's created.

[Lord_Melvin]

[QUOTE=McDunkable;50310984]Well, obviously it's a null entity, nowhere in the code do I see another instance of "ThrowChair" as an entity...

If you take a close look at the wiki, it says its first argument is an entity and ThrowChair isn't an entity, it's a method of "SWEP". Replace "ThrowChair" with "ent" which is the entity the SWEP creates. Finally, as previously mentioned:

Make a reference to the return value of util.SpriteTrail, which is another entity, so that you may remove it when the thrown entity is removed, or manipulate it after it's created.[/QUOTE]

Sorry for being so needy but how would I store the return value to a variable? Like this?

local trail = util.SpriteTrail( ent,0,Color(255,163,128,255) ,true, 100, 100, 2.5, 0.0025)

Once again, sorry for being so hopeless. I'm new to lua and I should probably already know how to do this. :frown:

[McDunkinY]

Like that, except make it a variable of the thrown entity itself, that way you can access it outside of that scope, as in your example, it's a local variable.

ent.trail = ....

You should probably keep track of the thrown entities as well by adding them onto a table of SWEP then removing them as they get removed.

[Lord_Melvin]

[QUOTE=McDunkable;50314621]Like that, except make it a variable of the thrown entity itself, that way you can access it outside of that scope, as in your example, it's a local variable.

ent.trail = ....

You should probably keep track of the thrown entities as well by adding them onto a table of SWEP then removing them as they get removed.[/QUOTE]

I got this error:

[ERROR] addons/one piece swep/lua/weapons/weapon_punch/shared.lua:101: bad argument #9 to 'SpriteTrail' (string expected, got no value)
1. SpriteTrail - [C]:-1
2. ThrowChair - addons/one piece swep/lua/weapons/weapon_punch/shared.lua:101
3. unknown - addons/one piece swep/lua/weapons/weapon_punch/shared.lua:46

Here is my code:

function SWEP:ThrowChair( model_file )

	--
	-- Play the shoot sound we precached earlier!
	--
	self:EmitSound( ShootSound )


	--
	-- If we're the client then this is as much as we want to do.
	-- We play the sound above on the client due to prediction.
	-- ( if we didn't they would feel a ping delay during multiplayer )
	
	
	
	--
	if ( CLIENT ) then return end

	--
	-- Create a prop_physics entity
	--
	local ent = ents.Create( "prop_physics" )

	--
	-- Always make sure that created entities are actually created!
	--
	if ( !IsValid( ent ) ) then return end

	--
	-- Set the entity's model to the passed in model
	--
	
	ent.trail = util.SpriteTrail( ent,0,Color(255,163,128,255) ,true, 100, 100, 2.5, 0.0025)

	
	ent:SetModel( model_file )

	--
	-- Set the position to the player's eye position plus 16 units forward.
	-- Set the angles to the player'e eye angles. Then spawn it.
	--
	ent:SetPos( self.Owner:EyePos() + ( self.Owner:GetAimVector() * 16 ) )
	ent:SetAngles( self.Owner:EyeAngles() )
	ent:Spawn()


	--
	-- Now get the physics object. Whenever we get a physics object
	-- we need to test to make sure its valid before using it.
	-- If it isn't then we'll remove the entity.
	--
	local phys = ent:GetPhysicsObject()
	if ( !IsValid( phys ) ) then ent:Remove() return end


	--
	-- Now we apply the force - so the chair actually throws instead
	-- of just falling to the ground. You can play with this value here
	-- to adjust how fast we throw it.
	--
	local velocity = self.Owner:GetAimVector()
	velocity = velocity * 100000
	velocity = velocity + ( VectorRand() * 1000 ) -- a random element
	phys:ApplyForceCenter( velocity )
	
	
	timer.Simple(2.5, function()
	if ent:IsValid() then ent:Remove() end
	end)
	--
	-- Assuming we're playing in Sandbox mode we want to add this
	-- entity to the cleanup and undo lists. This is done like so.
	--
	cleanup.Add( self.Owner, "props", ent )

	undo.Create( "Thrown_punch" )
		undo.AddEntity( ent )
		undo.SetPlayer( self.Owner )
	undo.Finish()
end

[editline]14th May 2016[/editline]

Nvm I got it working!