Snow/Mud Trails - Explanation of PC/Mobile Differences

Hello! I followed this tutorial to create snow trails: Creating Snow Trails in Unreal Engine 4 | Kodeco

Since mobile doesn’t support tessellation, I modified it to use World Position Offset with a highly subdivided plane. I noticed a couple differences between the PC and mobile versions. Specifically, on mobile:

  • The snow begins to deform at a much higher height above the actual surface (objects that are many centimeters away from touching the snow will still cause it to deform)
  • It seems like the render targets backing the effect are of significantly lower resolution (snow deforms around the whole character instead of just around the character’s foot) (does the engine automatically downscale render targets on mobile?)

Here’s 2 videos demonstrating the difference between PC and mobile (I used mobile preview, but it also looks the same on my phone):



I understand that the engine cuts some corners on mobile, so you can’t expect things to look the same between the 2 platforms. I’m really just curious about the first point above; what’s causing objects to deform snow when it’s not even close to touching it?

It’s as if the calculation which uses the depth pass to find the distance from snow is being offset somehow. Could this have to do with low float precision on mobile?

Btw, here’s how the amount of deformation is calculated (taken from the tutorial):

It basically uses a scene capture with custom depth and some distance calculation to determine if an object is within the 25 unit frustum in which snow deforms.

interesting. maybe both the uv and depth buffer are lower precision hence this result.
curious to know the actual cause.