Major differences between gz and zdoomgl from the same date?

[invictius]

Did they have the same features at one point and then just fork off? Or were there some wads that would only run on one or the other?

[Graf Zahl]

They have completely different roots. GZDoom incorporated some code from ZDoomGL, like some of the GL init code, the sky drawer and the parser for GLDEFS (the latter one was a big mistake in hindsight, I should have developed a better format...)

The renderers themselves share absolutely nothing. GZDoom grew out of PrBoom, although even in 2005 only a very minimal amount of PrBoom code remained - ZDoomGL was an independent piece of work. The main reason I pushed GZDoom to release back then was because overall ZDoomGL was not really a usable port, it had no support for render hacks, it got extremely slow on larger maps and it completely depended on the texture management for the software renderer, i.e. it converted everything to 8 bit, even if the source material was of better quality. Aside from taking the abovementioned bits of code, the biggest relation they share was that GZDoom's release prompted the cancellation of the ZDoomGL project. Apparently Timmie already had lost interest but considering how far behind in development ZDoomGL was, he no longer saw a point to continue his work.