(MBF21) Triggering Sky Transfers

[Novaseer]

Is it possible to trigger a sky transfer with a voodoo doll (as opposed to having that sky transfer automatically occur at map start) with MBF21?

 

I ask on behalf of my map for NOVA IV - as part of its final fight I want to change the sky across the entire map from the default blue sky to a red hellish one. I know an effect like this is done in Eviternity II's MAP30, but I'm not sure if that's a 'real' effect or simply a wall lowering to reveal another sky behind it - and a 'cheat' like that isn't feasible for my map as the geometry is far too complicated.

[Aurelius]

You can make a "composite" sky texture with two different skies stacked vertically, then use a displacement scroller to instantly scroll from one sky to another. This trick was used in Jumpwad MAP07. Here's an example wad using the MBF21 displacement scroller.

 

Unfortunately this doesn't play well with GZDoom, though you might find some sky dimensions and/or offset to make it work. Alternatively you can add some GZDoom only alternative using LOADACS, but it's a bit more work.

[Novaseer]

8 minutes ago, Aurelius said:

You can make a "composite" sky texture with two different skies stacked vertically, then use a displacement scroller to instantly scroll from one sky to another. This trick was used in Jumpwad MAP07. Here's an example wad using the MBF21 displacement scroller.

Thank you, I'll see about getting such a sky added to the project's resource WAD.

[Ribbiks]

It's worth noting that when I was toying with the jumpwad07 sky I found the effect wasn't perfectly consistent across ports, with prb+, glb+, zdoom and gzdoom all being a little different. It was basically unsalvageable in the gl renderers that I tried, so I wound up using GLDEFS (or GLBDEFS for prb, which is a pretty obscure feature) to swap out the composite sky for a static one, with the rationale that no effect > broken effect. Here's a table I made to document which ports worked and which didn't:

 

 

I was messing with this in 2020-2021, so it's possible the situation has improved. If I were to do it nowadays I would also test it in dsda-doom (software + gl-faux-software + with and without freelook for each) and also woof.