The existing decal effect is based on the Parallax mapping algorithm, but it can only express the effect of depressions(concave down effect). Because it considers 1 as the height of the model’s surface and 0 as the height of the depression. What do I do when I want to express a bulge effect(convex looking)? For example, 0 is the lowest and 1 is the highest.
recreate the shader and subtract the value by .5f and then mutiply by two, this will make your number range from -1~1
when authoring your displacement texture, gray will now be the surface height, towards black will be concave, and towards white will be convex
i’ve never used parallax though, so i don’t know if the algorithm even supports convex objects
you could also try normal maps to make the illusion of bumps/ perturbations