I found a way to make the game use a higher resolution texture for Slave Zero (just the player model, nothing else) in the Glide video mode.
This texture is the one the game uses when bump mapping is enabled in Direct3D.

Performing the following might prevent bump mapping from working in Direct3D mode.

Instructions (I'm assuming the directory and file structure is the same for the GOG version as it is for the CD version):

1. Navigate to your Slave Zero install directory and open the "Data" folder (eg. C:\GOG Games\Slave Zero\Data)
2. Make a back-up of "textures.zip"
3. Extract "textures.zip" using WinRAR or 7-Zip to a new folder
4. Rename or delete "textures.zip"
5. Locate the following files in the new folder:

a_Slave0_live_Limbs.tex
a_Slave0_live_Limbs_hires.tex
a_Slave0_live_Torso.tex
a_Slave0_live_Torso_hires.tex

6. Delete "a_Slave0_live_Limbs.tex" and "a_Slave0_live_Torso.tex"
7. Make a copy of "a_Slave0_live_Limbs_hires.tex" and rename it to "a_Slave0_live_Limbs.tex"
8. Make a copy of "a_Slave0_live_Torso_hires.tex" and rename it to "a_Slave0_live_Torso.tex"
9. Use WinRAR or 7-Zip to add the contents of the folder to a new zip archive called "textures.zip". Move it into the "Data" folder.
10. Play the game.

??: If something went horribly wrong or you want to get bump mapping to work in Direct3D again, delete "textures.zip" and replace it with the back-up.

| [url=http://i.minus.com/iqfJpDQcSL6qv.jpg]AFTER (shadows disabled to make it easier to see the texture)

| [url=http://i.minus.com/iihHeTjpvOdFi.jpg]AFTER

thanks for the info

i will try that the next few days.

are the other textures also better in bump mapping or is it just and only the player model of slave zero ?

Just and only the player model of Slave Zero from what I can tell - I haven't seen anything else in-game using bump-mapping and the only texture files that mention bump-mapping or hires in their filenames are for Slave Zero.

i had to amke the textures.zip write protected.
otherwise it rebuilt the originals lowres textures

but the rest worked just fine thank you

Hmm.. maybe the .zip has to be compressed a certain way for the game to read it correctly.
(the texture it's looking for is PHONEY64.tex)

These are the settings I used in WinRAR to make the zip.
These are the settings I used for 7zip.

(I would upload my textures.zip somewhere so that this tweak doesn't require as many manual steps, but I'm not sure uploading a large chunk of the game would be allowed)

Still no luck, I'm afraid. I realized one problem might be be running the game through the direct 3d .exe that was linked in another thread here, but... no. Trying to re-install the game with the original setting and put in the modified .zip file makes the game quit instantly, it still refuses to start.

I'm not the biggest tech wiz here so if it's not compression that's the problem, I dunno what is. Weird.

When you created the new zip file, did you add the entire folder "textures" to the zip, or just the contents of the folder?

If the texture files are inside a folder in the zip the game won't be able to find them (and will display the PHONEY64.tex error)

Contents of textures.zip should look like the left

Oh yeah it works now, awesome. :O

I just feel kinda silly now, I don't compress stuff often so I figured it'd be kinda self-explanatory that it wouldn't compress the way it initially did.

Thanks for the help!

It's possible edit .tex files?
I didn't manage to open them yet.

I haven't found a way to edit them.
I think it's a proprietary format containing the full-size texture and mipmaps, with some type of compression applied.

Apparently there is/was a development tool called "Texer" which can convert .tga and/or .flc images into .tex files, but I don't know if it's still available anywhere. If it could be found it might make texture replacements possible.

They made a plugin for those textures: http://forum.xentax.com/viewtopic.php?f=18&t=19293&p=147337#p147337
Btw I got some off topic questions:
1) I still don't know which mode is better for the game, d3d or nglide?
2) Usually my game crash on apolcalypse a or b when I am fighting the slaves: http://i.imgur.com/bekkG8e.jpg, still don't know why this happens, and i noticed it's a common issue online
3) Can't host muliplayer maps, it freezes instantly in both nglide and normal game, don't know how fix that.

Nice, that seems to work perfectly for viewing and extracting the base textures: screenshot
I downloaded Noesis from here, downloaded the script zip from the post you linked and extracted the tex_SLaveZero_tex.py file to \noesisv436\plugins\python

Now to find a way to get modified textures back into the .tex format...

1. In the past I recommended nGlide as it was probably the most stable way to run the game and allowed bypassing the crosshair offset issue via resolution forcing. Now it's possible to run the D3D renderer using dgVoodoo 2, which also offers resolution forcing and can be combined with the Direct3D / widescreen patch if desired. I haven't played enough to compare stability against nGlide.

2. Unfortunately I haven't found a reliable way to avoid that issue. Upper City A crash can be avoided by destroying them at long range (without using missiles), but the one in the tunnels on Apocalypse B is almost guaranteed to cause a crash - I only managed to get past (after many attempts) by looking in the opposite direction from the enemy and running past as quickly as possible.

3. I haven't actually tried multiplayer before now, but the levels seem to be loading okay using the Direct3D patch and dgVoodoo 2. No idea if getting into a match with another player is possible.
Note: I'm using an old retail copy of the game and Windows 7 - I don't know if the GOG version and/or Windows 8/10 will result in different behaviour.

Nice to see the script working, i also managed to find texer and other tools on my old slave zero iso (lucky me), I uploaded them on google drive: https://drive.google.com/open?id=1kvgf_p0CwCvdKPoFfcGBL91ljv1WeXa3
Thanks for the other tips for graphic setup, and multiplayer, the only remaining issue is the bugged enemy, i thought it could be a problem with the address for his health value, but sometimes crashes when you just see it lol
Needs a good debug way to figure out why that happens.

Ah, so it was on the CD the whole time... I'll have to dig mine out of whichever box it ended up in a while ago and see if there's anything else I missed on there.

There's something particularly weird about the Apocalypse B enemy - sometimes I seem to get teleported into the alcove he's in just before the game crashes. Occasionally Slave Zero will get knocked over as though hit by a railgun attack, but the nearest enemy with one of those is several rooms away...