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[GZDoom] Sector portals, green DoomGuy apparition

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Hello All,

For my new map I am using Sector portals for the first time. I think I managed to set up the portal correctly, but if I go through it at high speed the green marine appears for a brief, yet noticable moment. When I go slowly then everything seems correct.


Can you help me with getting rid of this apparition?


See the video:


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Thanks Aquila, and yep, solving this issue was a personal mission of mine for quite some time! 


The problem is down to the interpolation code in GZDoom (I believe).  As the game tries to smooth out your sprite movement between tics, it means your sprite's position and your actual position can every so slightly differ from time to time.  Usually this isn't an issue, but when you go through a portal at a fast enough speed, your sprite can actually pass through the portal before you do, meaning you see your own back for a moment.


Without rewriting the interpolation code, the only remaining solution is to hide the player sprite.  There are no default ACS commands to do this in GZDoom without also hiding the weapon sprites, so the solution requires a bit of a work-around.  The most basic approach would be to include new player sprites in your WAD that are completely invisible.  The plus side is that it's easy, the downside is it breaks co-op and third-person cameras. 


The solution in the above thread was my attempt to achieve that without changing the player sprites, rendering you invisible only briefly.  Instead of editing the sprites, I created a custom Player Class that turns invisible once a specific new Power-Up is given.  You can set the Power-Up to last say a few seconds and then give it to the player just before they pass through the portal, rendering them invisible only briefly (and thus only briefly breaking co-op and third-person cameras). 


All in all, it's a bit of a pain.  My personal advice would be not to worry about it if you only have a handful of portals, as it may get fixed in a future version of GZDoom.  I created a map in Elementalism that has well over 100 portals in it, so I had to come up with something, but otherwise it might be better to just try to ignore it.

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Which version of GZDOOM are you using?

I had a problem like this in January with GZD-x64 g2.4pre-42, which was then fixed in version 2.3.1.

I haven't had any problems since, with GZDoom now at GZDOOM- g3.7pre-210.

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1 hour ago, Kappes Buur said:

Which version of GZDOOM are you using?


It very much still happens with the latest builds unfortunately.  I had no idea the devs had attempted to fix it, whatever they tried unfortunately hasn't seemed to have worked.  I wonder if it was solved for certain situations but not all of them?

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Thanks for the feedback. Now at least I know that it's not my fault with setting the portal incorrectly.


I will experiment with the proposed soultion even though it seems to be extremely "hacky" :)

The advise to ignore the issue is also very tempting :)


@Kappes Buur, I observed it with GZDoom


BTW: After reading through your post on drdteam I see that you had this problem with line portals. For me it's not the case. In the map I released recently (link below) I used the line portals to great extent and never observed any green marine appearing. This only happened to me once I started experimenting with sector portals.



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