[f1bb767] Performance regression when running Project Brutality

[argv]

In the latest dev build (f1bb767), I'm seeing some serious performance issues in Project Brutality compared to GZDoom 2.2. “stat rendertimes” shows finish times spiking: 20+ one time, then 10 or below, then 20+ again, and so on.

While this is happening, there are a lot of sprites on the screen (800 to 1200). There must be more to it than that, though, because I wrote a test actor to generate 1000 sprites for a moment, and that didn't cause this problem.

Environment (see also attached DxDiag report):

• Windows 7 64-bit
• AMD Radeon R9 290x
• Radeon Software 16.8.2 (Crimson)
• GZDoom f1bb767 Win64 from DRD Team dev builds site

To reproduce:

1. Load doom2.wad, Project Brutality 2.03, and Doom 2 The Way id Did.
2. zdoombrutaljanitor 1;sv_cheats 1;skill 4;map map07
3. god
4. Step forward through the door and teleport line.
5. Kill the Mancubi.
6. Let the Arachnotrons and Spider Mastermind shoot at you. The frame rate should tank.

The same problem can also be seen on Doom 2 map07, but it is less pronounced. I'm guessing the inclusion of a Spider Mastermind on D2TWiD's map07 makes the problem worse, somehow.

[Graf Zahl]

Can you narrow it down to some specific devbuild?

[argv]

Ok, I'll work on that. Give me a while.

By the way: the software renderer doesn't show this problem. Frame rate stays at solid 60 (if translucent sprite rendering is turned off, but that's another story).

[argv]

The problem shows up in the build of 750c194. It is not present in the build of d655892. Backing out that commit seems to solve the problem.

[Graf Zahl]

I added a new CVAR gl_finishbeforeswap which can optionally restore the old order. Please check this so I can close this report and finalize the implementation.