Allow transparent parts in translucent FOF and PolyObject planes

Until now, transparency in FOF flats (via the cyan = invisible hack) was only possible if you gave the FOF FF_TRANSLUCENT but set the alpha value to 256. This meant that actually translucent FOFs couldn't have transparency. The situation for PolyObjects was similar. This was despite the fact that a rendering routine that allows for both transparency and translucency does exist. This branch adds the ability to enable cyan pixel cutting explicitly via the ML_EFFECT6 flag, making translucent flats with transparency possible. To ensure backwards compatibility, the old methods for enabling transparency still work.

• srb2win-splat.exe
• splat.wad

Now that, since v2.2.1(?), wall textures can be used on floors/ceilings, is this beneficial when compared to using actually-transparent textures instead of "hacky" cyan-transparent flats?

I mean, sure, more options are always nice, especially when this has already been coded... but is this actually useful anymore?

(Disclaimer: I don't know whether or not transparent textures currently work for translucent FOFs/PolyObjects.)

Yes, because transparent textures currently don't work for translucent FOFs/polyobjects: their actually-transparent areas will show up as cyan when used as a flat, as can be seen in the provided example map.

merged

mentioned in commit 50b47a1b