It depends on what you call a detail texture. Be a bit more precise, just tell us exactly what you need, or what effect you want to achieve.

If you mean a highly tiled texture gradually blended on the terrain, depending on camera distance, then there are several ways.

You can simply compute the radial distance between the camera position and each vertex of your mesh. Then derive a blend factor from this value and blend a second (highly tiled) texture on the terrain using this factors. You can do it single or dual pass. You can cut the detail maps after a certain threshold distance, if the factor gets zero.

Then there is the mipmap trick. You always need two passes (or two units), on your whole terrain for that. The trick is to use a special mipmap in the alpha channel of your detail texture, that gradually fades out with higher mipmap levels. The you blend your detail texture based on this alpha. It''s rather easy to implement, but looks not very good IMO. And you _need_ trilinear filtering, or it will really be ugly.

And finally you have some more complicated methods using VPs and regcoms.

/ Yann