At this moment I'm working on materials blending.
The industry standard for this is more or less what's called height based blending. It's the blending mode, where two or more materials are mixed not only according to their distribution weight (which alone would give a very flat featureless picture), but with respect to the height/displacement provided along with texture materials as well. Here's the good explanation of what is materials blending and what each blending mode looks like (I'm aiming to replicate the look of the last picture):
http://www.gamasutra.com/blogs/AndreyMi ... atting.php
As always couple of pictures of what's been achieved so far:
Here you can see the gravel and ice material are mixed together linearly from left to right. The most interesting part is what happens in the middle, where both weight (changing from left to right) and height (which is the property of each material) play nicely together.
And here's the zoomed in fragment, it's placed around the middle of the map, as described above. On the left side the gravel is almost "pure" with very little perceived amount of inclusion. In the middle, we can see ice patches occupy cracks between individual gravel stones. On the right side, ice has almost replaced the gravel patches as the latter are barely visible.
What pictures above lack is the sense of volume, which in case of spring can be only emulated by use of the parallax occlusion mapping (POM).
Unfortunately with such diverse set of materials and the way they are currently described in Lua, the implementation of POM looks rather complicated, so it remains my stretch target. Practically this means, that I only do it in case there is some real interest/demand from the artists (see my previous post).
In the mean time you can entertain yourself by looking how materials blending might work with POM here: https://shaderfrog.com/app/view/2818