Ok, So I have this great landscape engine happening. It works beautifully. It uses multitexturing. It runs really well on a GF1, and someone said it actually runs ok on a TNT2 they tried too. Because of this, I wanted to only have to use two textures at any one time, because more would mean multiple passes, which I dont really feel like doing for a number of reasons. I had this plan whereby I would have two textures at any time for each patch - one "general", which would get tiled across the whole map, and one "specific", which would be specific to that patch. IE: "general" texture is the "feel of the map" (grass, sand, snow), "specific" texture is the "feel of the local area" (rocky, steep, muddy). The two would be blended by a function of altitude and gradient (like everyone else does). That ties up the two texture units, so I was using standard GL lighting as well. Which is also good seeing as the maps are randomly generated, and generating huge lightmaps from random maps at load time is a hassle. The theory was that I would use gl_arb_texture_combine, and its nice gl_interpolate mode to blend the two. I was thinking that I could set the first texture unit to simply render normally, then set up the second using interpolate_arb, taking the "previous" color, and the second texture, and blend based on alpha, which would be specified in a pre-computed color array (I am using vertex arrays, etc). But it doesnt work. I can get it to interpolate based on color, so you get the dark bits (due to lighting) replaced with the second texture. Which is entirely not what I want, obviously - kinda defeats the point of lighting, and the whole point is to be able to blend through where I choose, not where the light happens to make dark bits/shadow. I have seen a demo where the guy has two textures, and blends between the two based on the alpha he specifies using straight glColor4f() calls, so it *should* work - I am effectively doing exactly what he is doing. So I guess what I am asking is, is there any way to do lighting as well as arbitrarily blended textures on two texture units using env_combine. Or any other method. OR am I going to have to do multipass, and even then is it possible? HEEEEEEEELLLLLLLLLP MEEEEEEEEEEEEE!!!!!!!!!!!!!

Ok, I think I got something sorted. Am I right in assuming that interpolation doesnt work properly with lighting? If you turn lighting off, it seems to work fine.

Which is a pain in the butt, cos I wanted to use gl lighting.

Anyone know if lighting is the only problem I was having, and whether or not there is a way to do GL lighting as well as interpolate between two texture units based on alpha?

Multiple passes maybe?

How about using another texture unit?