Glidos' shadow hack in Tomb Raider 1

I always wanted to ask Paul, but never did.

What's the thing with the shadow hack that Glidos can fix ?

I asked recently the authors of Dosbox (which via the Glide patch actually doesn't get to produce Lara's shadow) but they don't know much about it.

My question is : is that a hack that really fixes a glitch in the original Voodoo Rush version (since "straightforward" software TR1 does have the shadow after all) ?

Is that a trick made tweaking the Glide to OpenGL wrapping ?

Just for the sake of clearing my mind about it.

Thx for reading. 

I can't really say I've ever gotten to the bottom of it, but yes, I think the voodoo rush version of Tomb.exe has a glitch.

Glidos gets around it, by recording the constant colour when TR1 set the alpha source, and then reenstating that colour every time TR1 uses transparency.

Paul Gardiner <...> said:

Glidos gets around it, by recording the constant colour when TR1 set the alpha source, and then reenstating that colour every time TR1 uses transparency.

in the wake of your hint, and also after fetching an old post of yours at vogons

http://vogons.zetafleet.com/viewtopic.php?t=2213

where in 2003 you wrote : I think there may have been bugs in early versions of Glide that TR1 then relied on. Something like the alpha unit having its own cache of the constant color value that doesn't get updated if the alpha unit is off... or something completely different

I tried to understand more about it and shoveling and fiddling with the open source of glide patch by gulikoza (dosbox cvs builder) who kindly helped with compile instructions for mingw\msys and stuff, I guess I came to a solution of sorts by tweaking a bit Glide grConstantColorValue(), which hopefully would aim to follow your steps, I compiled it and it seems to work.

Is it alright for you if I discuss it here ? Or, if you don't care, better to address vogons' forum ? Or what  ?