Multitexturing/Vertex Alpha question:

Example:
I have a mesh which I make to use as a terrain. I place two
greyscale textures on it, one on top of the other. Is it then
possible to change the vertex alpha of individual vertices so
that only one of the textures becomes transparent, or will it
do that for both of them?

Basically I want to be able to have regions on the mesh which show one of the textures and other regions where the other texture is visible.

VertexAlpha affects all textures AFAIK. Of course you could use multiple copies of the same vertices, representing individual Surfaces. Unfortunately this will double the polycount, but nice results are possible this way.

Thanks,

I feared that was the only way to do it, make a second surface and increase the polycount.

EDIT:

Actually there is another way to do it without using alpha blending that I will try later tonight.

Did this way work? ;)

The second method "kind of" worked. What I did was use vertex coloring rather than a texture for the terrain, then used 2 greyscale textures, the first as grass which was tiled across the terrain (static mesh terrain not blitz terrain). The second texture used the second UV set and was added with an additive blend. However the second texture had been designed such that when it was add-blended with the grass texture beneath it, you would not see the grass detail texture beneath the rocky bits - to do this I used a kind of "subtractive blend" to generate the texture.

If I had perservered with working on it I may have been able to achieve something useful with it, as it is it was more effort than I was willing to spend to get an effect that was not that great.