about adding textures to pwads

I feel this is much a newbie question, but I need to seriously get it right, if I'm to implement it on my maps.
Can I borrow a graphic from the IWAD, using SLADE, then change it a bit (say, spray it with 'blood'...) and save that into my pwad, so I can choose it in Doom Builder as textures for my walls?
anyway, how would I achieve that?

thanks for all the help.
cheers.

Typically, you'd export the texture to a file, modify it, then import that file as a new entry, select it, convert it to Doom patch format, and choose "add to TEXTUREx"; importing if needed the textures and patch tables from the base resource archive, which would previously set accordingly (doom2.wad for a Doom II mod, doom.wad for a Ultimate Doom mod, etc.).

For some ports such as ZDoom, you can simply import the modified file between a TX_START and a TX_END lump. You can also skip the conversion step if it's in a supported image format already.

pablogener said:

Can I borrow a graphic from the IWAD, using SLADE, then change it a bit (say, spray it with 'blood'...) and save that into my pwad

If the 'blood' patches (to borrow your example) have transparent backgrounds, another option is to learn the black art of texture lump editing and create new textures that way, instead of filling your PWAD with modified IWAD graphics.

I tried 'exporting' the textures in PNG format, from slade, but seems I'm missing a pngout.exe file that didn't come along SLADE.... would anybody know what/where that is? anyway, it's a nice idea, creating a 'patch' with the blood splat and 'patch up' other textures with that to create the effect of bloody walls.

If you're using the official v3.0.2 release I'd suggest you replace it with an SVN build. As for blood splats, they were used to create a number of textures in TNT.WAD, it'd be worth your while to take a look at how it's done and maybe borrow the patches for your wad.

pablogener said:

I tried 'exporting' the textures in PNG format, from slade, but seems I'm missing a pngout.exe file that didn't come along SLADE....

Exporting isn't optimizing. You don't need pngout to export.