Adding abs() to a displaced SDF allows the raymarcher to backtrack when it overshoots a surface

When a displaced SDF generates a negative value (the ray has passed inside a surface due to inaccuracy), the ray marcher normally keeps stepping in the same direction, getting further inside. Adding abs() around the distance field makes negative values positive — the marcher ‘backtracks’ and converges on the actual surface by oscillating around it. This fixes flickering artifacts from displacement without the heavy cost of halving the global step size. The ‘S’ in SDF becomes purely informational — it is no longer a true signed field — but this is acceptable for visual stability.

Examples

d = abs(map(pos)); // allows backtracking on overshot surfaces with displacement

Assessment

Compare the visual result of abs(map(p)) vs map(p) on a strongly displaced terrain when viewed from a grazing angle. What artifact does abs() prevent?