Hi
Yes that should be the default behaviour.
Mix mode in fact does an
"alpha over" operation on the background texture channel or base value, and that should be also the case for scalar textures. However, I believe that in this case we are supporting a legacy feature but it is badly implemented.
If I remember well, in YafaRay exporter previous to Blender 2.50 and in YafRay, there were in fact two settings called
Var and
DVar that controlled minimum and maximun range of the scalar texturing, respectively. For instance, if
Var=0.20 and
DVar=0.80 that would meand minimun and maximun ranges for black and white values in scalar textures, respectively. This workflow was copied from Blender Internal like so many texture related features.
Somewhere along the way Blender Internal dropped
Var setting but kept
DVar, while YafaRay exporter post Blender 2.50 adopted this strange workflow of doing scalar texturing, in which base value is used to set minimun range for black in scalar textures. That's why I am asking what
upper_value fval actually does in XML scenes as I suspect I may have something to do with the problem exposed here.
I would like that we have a clear view about the situation so we propose a rock solid consistent workflow from now on for scalar texturing.