View Full Version : Multitexturing Questions

10-29-2002, 11:13 PM
Hi all,
I just got a Geforce 3 and it's awesome! I am playing around with the 4 texture units on it. (well it has 4 per pipeline, maybe only two though? I get 4 per pipe so that's all that matters?).

I would like to know ways to combine textures togethor using multitexturing. I am building a landscape engine. I have my base texture, which I generate with a tool. I'd like to find ways to put details onto it.

What I'd like to do is somehow be able to put the higher frequency information in the textures onto the landscape. This way I get alot of detail. I don't know how to do this or generate the detail maps so they blend nicely togethor. I don't know how to make multiple texture units blend, modulate or put luminance onto the final output. I just know how to combine them but I don't know how to tell it how yet.

I read the OpenGL docs on the Multitexture stuff but it doesn't contain much clues how to use it just tech info about how it works.
Any information about how to do multitexturing with OpenGL around?

Also if I do bump mapping, does that take up a texture unit?


10-30-2002, 02:14 AM
Hi! Well... for multitexture you will need to use GL_ARB_multitexture opengl extension (http://oss.sgi.com/projects/ogl-sample/registry/). It's quite easy. I think www.nvidia.com (http://www.nvidia.com) has some demos about it and about about bump mapping as well.
For multitexuring you will need to load each texture unit with a texture and then draw your geometry normally but will need to specify the texture coordinates for each texture unit.
For bump mapping, you will need a normal map which contains the bumps so you will need to load it to a texture unit so you can perform per-pixel operations. For per-pixel operations check register combiners but as you have a GeForce3 you probably could do this with pixel shaders but about pixel s haders i don't know nothing because my graphics card is a GeForce2 http://www.opengl.org/discussion_boards/ubb/frown.gif.
Check www.nvidia.com (http://www.nvidia.com) , you have everything you need here!! http://www.opengl.org/discussion_boards/ubb/smile.gif

Hope this might help you.

10-30-2002, 02:53 AM
Hi yah,
Thanks for your help. I already know how to use Mutlitexture, the problem is I don't know how to work with it to get the results I want.

I figured out some ways to get what I want but it's not what I want to do exactly. What I do is convert my detail texture to grey scale. For some reason I can only load this into opengl using GL_RED as the channel. I have no idea how to load an 8-bit greyscale any other way with gluBuild2DMipMaps. Then it works.

What I really want to know is how to do alpha blending and blending and how to use modulation with multitextures to get cool effects. I realize that details should only be rendered in the nearby areas and turned off when viewing distant terrain because it looks funny otherwise.

Anyways in a couple more monthes GeForce 3 TI200 will be very cheap so you can upgrade. I got my TI200 for $99 which is the price I was waiting for. Before that I was using a GeForce 2 MX400, and then a Voodoo 3. I don't buy the latest graphcis cards anymore when it was all new I was buying a new card every couple of months. I have so many of them now it's pathetic. I think in a bout 3 months a Ti200 will go for $60-80 so you should be able to pick one up. THey are real sweet you have to see all the Cg stuff with them really cool stuff.

See yah

10-30-2002, 09:30 AM
About loading grey scale, I think its not worth the bother since I'm betting that most cards now convert to RGBA8888. GL_LUMINANCE is probably what you want with GL_UNSIGNED_BYTE.

To get the effect you want? You need to figure out how to setup the env combiners or better yet, use some 3D software.

Hooray for technology and the cheap prices! Unfortunatly I cant buy the hard disk I want because their out of stock for 2 weeks now!