Problem with tall sky rendering

[Graf Zahl]

I did some sky tests today to see how yesterday's changes affect the sky display when I noticed a problem.

If the sky is very tall (240 in this example) the top of the sky is cut off.

Here's the sky texture:



and here's how it looks in the game when looking fully up:



and when looking straight ahead:



As you can see on the first screenshot the uppermost part of the sky is not shown.

I couldn't find a single tall sky where this does not look like the intended positioning. It always looks like the sky is positioned too high. Wouldn't it be better if such textures were shifted down so that the top line matches the top of the screen?

[Enjay]

Would doing so mess up WADs where the author has spent time positioning his sky graphic based on Zdoom behaviour? It's quite a while since I used a single tall sky graphic for anything but I do remember that I would go back and forth between my graphics editor and Zdoom to ensure that the sky I was making looked as I wanted it to in the game.

[Graf Zahl]

No idea. I scanned through 100 WADs already and all tall skies I saw so far were of the kind where shifting the sky down looks better.

Maybe some advanced sky rendering options like explicitly specifying the position would be a good idea. Then we could add a compatibility option for affected WADs and if necessary handle them in compatibility.txt.

Based on what I saw I already made some changes to GZDoom which also had it wrong, but in a completely different way.

[randi]

Are all third-party tall skies taller than 200 pixels? They were only meant to be 200 pixels tall, but if everybody is making them taller, I suppose something should be done about it.

[Xaser]

I've always seen tall ones as 256, myself. Never had any idea that the actual intended size was less than that.

[Graf Zahl]

Are all third-party tall skies taller than 200 pixels? They were only meant to be 200 pixels tall, but if everybody is making them taller, I suppose something should be done about it.

I have seen several up to 240 (which all look strange) and created some 256 pixel tall ones myself.

I have addressed this issue in GZDoom today because I noticed that extra-tall skies didn't work properly there, too. But instead of being cut off at the top they were positioned too low because when I implemented them I used my own 256 pixel skies as guideline and I had the baseline placed far too high there (at y=160)

I've changed it now so that the baseline is always at y=200 for anything >= 200 pixels tall. Except for my own skies this appears to work fine with everything I checked. But to keep my own skies I'll add an offset option to ANIMDEFS so that I can easily reposition them. Could be used as a real feature...

[phi108]

Actually, back when I was manually stretching all skies in pwads that I played, I would stretch them or add stuff on top to make them 228 pixels tall, because that is the distance I deduced from looking at the bottom of the rendered sky up to where the vertical view stops.

I wondered why automatic stretching did it a bit differently.

(but for another complication, the new skulltag lets the software view go even higher, but I have it disabled with "cl_oldfreelooklimit 1". It doesn't change sky stretching though.

[Graf Zahl]

That would be a non-issue if the software renderer could expand the skies like GZDoom does in hardware mode. Yes, it would just be a solid color but is there really a better option?

[randi]

I've always seen tall ones as 256, myself. Never had any idea that the actual intended size was less than that.

It was 200 because that was what Heretic and Hexen used. They're the only games that had tall skies as standard features.

[Xaser]

Ah, that explains it. I take it that's the tallest the sky can be while still keeping the pitch clamped, which I assume works the same between ZDoom and Heretic/Hexen.

[Graf Zahl]

Hm. This doesn't work well for any of the skies I checked. I added a CVAR to toggle between the current behavior and how I think it should be and compared all the skies I found yesterday.

These are the WADs I checked:

The Darkest Hour (the moon and mountain skies)
Temple of the Ancients
Phoenix Rising
Paranoia
A Hex on You
The Chosen
Super Sonic Doom MAP10

In all of these cases it was beyond obvious that squishing the 240 tall sky to 200 is not the intended behavior. They look all better if left unsquished and having the base line moved down.
I'll try to find more skies but so far I haven't found any aside from my own that aren't just space clouds etc which aren't affected by positioning either way.

[edward850]

I'll try to find more skies but so far I haven't found any aside from my own that aren't just space clouds etc which aren't affected by positioning either way.

Zen Dynamics has tall skys, most notably map07. Not sure how tall they are though.

[Graf Zahl]

I'll check them immediately.

[Graf Zahl]

The skies in Zendyn fare even worse than all the others. They are caught somewhere in the middle with the base line at around 216 in a 256 pixel tall texture so they don't look right with either method without some fudging (like the skyoffset I implemented yesterday in GZDoom.)

But if I had to make a choice, Randy's squishing again loses clearly because the base line and the filler part below it becomes visible too obviously.

Here's 2 screenshots of Zendyn MAP07:

Squished: (see the darker part in the sky? That's where the base line is supposed to be. The lower part is just a darkened reflection of the upper part)




Shifted down: (it shows less of the mountains, of course but it also hides the parts that are supposed to stay hidden)

[randi]

Fine, whatever. I grow weary of fiddling with the sky.