ZDoom

if (true) { // insert CVAR here
	line.flags &= ~ML_MAPPED;
	line.flags |= ML_REVEALED;
}

Ok, so, I have it clearing off the "AM_MAPPED" flag and putting in an "AM_REVEALED" flag after it draws every line, so it only properly renders what the player can see and leaves the rest grayed out.
[imgur]https://imgur.com/gallery/fMsHzvA[/imgur]

I just need to put in a CVAR here:
[code]if (true) { // insert CVAR here
line.flags &= ~ML_MAPPED;
line.flags |= ML_REVEALED;
}[/code]

Ok, I'll implement that and see how it looks. What should I use for the internal condition to do this?

That's exactly what I had in mind. Adding something complex is out because this is a time critical loop. But clearing ML_MAPPED before starting the renderer is definitely an option.

Since you were asking me on the Discord, I might be able to implement a cheat code which causes the automap to remove all of the lines after every frame or possibly just highlight them. I'm already screwing with the automap code in my experimental build, but I'd have to look at the code for setting ML_MAPPED to see if there is an efficient way to do this.

You can disable wall rendering with gl_render_walls false, that might help.

From reading the BOA thread and trying to troubleshoot my own maps, a quick way to tell if a portal or area of the level is being occluded would make the process of tweaking performance on wide-open maps a little easier.