When I first heard of Delta’s Color Erosion I got an immediate picture in my head of what that might look like. Once I found the macros using it, I realized that it was just a distortion/displacement over split channels that, unfortunately, work more like X, Y offsets. The picture I had of colors running down flow paths was not possible without correct vectors-from-slopes.
Now that my new computer is here and I can get code devices to work, I took a shot at using the Flow Directions example. I think this is a good proof-of-concept, but for distances beyond a couple kilometers it doesn’t remain very physically accurate. Within those limits? Not a problem. Now it’s just a matter of splitting diffuse/albedo textures into channels, eroding, and then splicing them back together.
I thought the same thing. I went on to use an equalized flow-soil average (50%) mask on displacement. I did the same with a modified flow directions (taking best from all four cardinal directions - lower branch).
Before there was a Code Device, I would use the angle output from Select Aspect masked by flow for this, but the displacement was more lateral offset than following the steepest slope from high to low elevations. Having seen the map produced by Flow Directions, I see that it would have worked better using the main output of Select Aspect with a heading of 0 and elevation of 45 degrees.
Edit: I took a closer look at my original pass and saw that I was wrong about the distortion following flow paths strictly from high to low elevation. It’s still displacing sideways, so on one side of the mountains it looks the way I pictured, but the opposite side looks like material flowed upslope instead!
Ah, well. I can kludge something together for the right effect with two passes (or maybe four?) and splice them together with aspect masks.
The effect I’m going for can be illustrated with colorizers using two leveled heights at 1-normalized-gamma+2 fed into 2-gamma+2 averaged together using the flow-soil mask from before.
Since I got what I intended in Filter Forge I played a little to get the correct angles in Aspect devices and used them for vector displacement. This produced the effect of material following flow, rather than going against it in half of the terrain.
