Fix incorrect object placement with A_SpawnItemEx

[Jekyll Grim Payne]

If you use A_SpawnItemEx to spawn something like a light halo for a flying projectile, even if you use 0,0,0 coordinates, the halo will look like it appears in front of the projectile and then jitters back; it only looks absolutely right when you use 'freeze' command.

The same problem arises if you try to use FastProjectile and make the halo object spawn via MissileType: they jitter back and forth (if the projectile has a regular speed, not what FastProjectile is usually used for).

I decided to create a singular halo that just uses the same velocity as the projectile and dies with it. However, if it spawns at the same time as the projectile, it'll appear 24 units in front of it, not at the projectile's position (even with 0,0,0 coordinates). So I used this:

Code: Select all

Actor BD_Plasmaball : Plasmaballreplaces Plasmaball
{  
+DONTBLAST
damagetype PlasmaDamage
+FORCEXYBILLBOARD
+THRUGHOST
+NOEXTREMEDEATH
+BLOODLESSIMPACT
decal BluePlasmaSplat
renderstyle ADD
scale .2
alpha .5
States
	{
	Spawn:
		TNT1 A 0
		TNT1 A 0 A_SpawnItemEx("BlueFlarePlasma",-24,0,0,velx,vely,velz,0,SXF_SETMASTER|SXF_ORIGINATOR|SXF_ABSOLUTEVELOCITY)
		PLBA ABCDEF 2 bright
		goto spawn+2
	}
}

Actor BlueFlarePlasma
{
+NOINTERACTION
+NOGRAVITY
renderstyle Add
alpha .5
scale .1
states
	{
	Spawn:
		LENB A 1bright
		loop
	}
}

It does look like the halo is perfectly matched to the projectile... As long as you're shooting horizontally. If you shoot diagonally up or down, the halo will naturally be skewed in space.

Is there any way I could adjust the formula so that it appears in its proper place?


For reference, if I use 0,0,0 coordinates, it'll look like this (this is view from the side with 'freeze', not from behind):



Note that in this case the halo somehow spawns in front of the projectile but it DOES take its pitch into account; while according to the wiki it's impossible to truly account for projectile's pitch.

[Apeirogon]

Try warp instead spawn, like

Code: Select all

Actor BD_Plasmaball : Plasmaballreplaces Plasmaball
{ 
+DONTBLAST
damagetype PlasmaDamage
+FORCEXYBILLBOARD
+THRUGHOST
+NOEXTREMEDEATH
+BLOODLESSIMPACT
decal BluePlasmaSplat
renderstyle ADD
scale .2
alpha .5
States
   {
   Spawn:
      TNT1 A 0 nodelay A_SpawnItemEx("BlueFlarePlasma",-24,0,0,velx,vely,velz,0,SXF_SETMASTER|SXF_ORIGINATOR|SXF_ABSOLUTEVELOCITY)
      miniloop
	  PLBA ABCDEF 2 bright a_warp(aaptr_master, 0,0,0,0, WARPF_NOCHECKPOSITION|WARPF_MOVEPTR|WARPF_INTERPOLATE|WARPF_WARPINTERPOLATION)
      loop
   }
}

[Jekyll Grim Payne]

Try warp instead spawn, like

It would make more sense to use A_Warp on the halo instead of the projectile, otherwise it'd change the position of the actual projectile. You're right, they can be combined (I tried A_Warp before but without combining it with this method), and it's very effective, it does indeed fix the halo's position. Thanks!

[krokots]

I encountered this "jittering" in my projects. Did you try to change angle of the "effect" so that is angled always towards player? Maybe that will stop the jittering, but I don't know. I just left it as it is in my mod.

[Void Weaver]

miniloop

o_0 What is "miniloop"?! I never saw such instruction before, how it work?

[Nash]

miniloop

o_0 What is "miniloop"?! I never saw such instruction before, how it work?

There is no such thing in the entire source code so I assume author made a mistake in that post.

(Source: every State-related instruction can be found inside ParseStates inside thingdef_states.cpp; on top of that, a global search for "miniloop" in the entire source code returns 0 results)

[Mikk-]

I think it’s supposed to be a custom state, however he forgot the Colon