Slope Mask From Normal

Real materials don't wear evenly. Dirt settles on top surfaces, grime collects in crevices, paint chips off edges that face up into the weather. Recreating that in a texture by hand means painting masks for hours. x1SlopeMaskFromNormal does it from the normal map in about a second: it reads which way every surface is facing and emits a mask of exactly the faces you asked for. This is the same trick Substance Painter's slope masking does, and it's a small node in ComfyUI that saves you a lot of manual masking.

How it works

A tangent-space normal map stores surface direction as RGB - the X and Y channels encode tilt, the Z channel encodes how much the surface points up out of the plane. The node decodes those channels and extracts the one you pick with mode:

• +z (default) - surfaces pointing up (flat tops, horizontal ledges). Perfect for dust and fallen-leaf debris.
• -z - surfaces pointing down (undersides, ceilings). For grime that hangs, or moisture that collects underneath.
• +x / -x, +y / -y - the four wall directions. For one-sided weathering like north-side moss or wind-driven rain streaks on a specific face.
• rim - the special one: it's 1 - Z, so it highlights everything not pointing up, i.e. all the sloped and vertical geometry at once. Great for edge-wear before you split it further.

strength (1.0) scales how aggressively the mask responds, and gamma (1.0) reshapes the falloff - lower gamma pushes midtones toward white, which fattens the masked areas. invert_values flips it, which you'll want constantly (dirt on +z means dust on tops; invert for grime in crevices).

The inputs that matter

Unlike the JSON-blob MKRShift nodes, this one is all discrete widgets, and there are only a handful:

• mode - the direction dropdown. This is 90% of the node.
• strength (1.0) and gamma (1.0) - how strong and how soft.
• invert_values - flip the mask.
• mask_feather (8.0) and invert_mask - the output feather, plus an optional mask input to restrict where the slope mask is even emitted.

Outputs are image (the grayscale slope map, viewable as a texture), mask (the same thing as a MASK you can wire into a blend, a roughness map, or any other map socket), and slope_info (a text summary). Feed the mask into the pack's x1SurfaceDustMask or x1EdgeWearMask as a source mask and you've built a full weathering stack without painting a single pixel.

Installing it

Part of the MKRShift Nodes pack. ComfyUI Manager: search "MKRShift", install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/criskb/MKRShift_Nodes

Restart after. No models to download - pure numpy on the normal map.

Gotchas

The normal map needs to be tangent space (the standard R+G = tilt, B = up encoding) or the directions come out meaningless; a world-space normal from a photo scan will produce a mask that's correct in spirit but misaligned with your UVs. Also, this works on the geometry direction, not on height or cavities - if you want dust in crevices, use a cavity or AO map instead of this node. They solve different problems and you'll reach for both.