Due to an ongoing thread at the Polycount boards about the snow and ice of Uncharted 2, I replicated Paul Greveson aka MoP’s vertex blending material in Unreal.
This is my result:
The tank tracks are another type of blend, this one’s about the snow on the ground.
I was asked to post my node layout on my blog, so here goes:
The base mask for snow coverage is calculated by using the Red vertex color channel (you can easily paint onto one channel only in UDK, great feature!) and a heightmap. These are combined together to create a transition effect with the heightmap, where the vertexcolors fade out. Clamped at the end to prevent extreme values, just for safety.
Using the Green vertex channel, we calculate a varying number for the mask’s hardness. 20 is the ceiling value, a 1 is added to prevent powering to 0 (bad). The invert on the vertex color is just to make sure the default value is hard (default vertex color is 1,1,1,1).
Both groups are combined by powering the raw mask to the hardness value, adjusting the contrast. Clamped for safety, though technically not necessary since we’re only powering a value of max 1to20,resulting in a 1 anyway.
The mask is used on 3 LinearInteroplate nodes, to blend between snow and non-snow diffuse, spec and normals. Since I had the heightmap anyway, I just used it for a quick parallax effect on the diffuse (I should apply it to normals as well…).
Total material. Nothing too complex, only 63 instructions which really isn’t expensive.
I recommend doing this in UDK only, since painting vertexcolors is incredibly easy there.