stoneTriplanar

A stone projected from three sides in the object's own space, in metres, for boulders, rocks and terrain pieces with no usable texture layout. The vertex stage hands the fragment the object-space position; the fragment rebuilds the object's rotation from screen derivatives so the three normal maps point the right way. The texture stays put on a boulder that is moved, turned or rolled, keeps real scale (tile_size metres per repeat) however the boulder is stretched, and fills a PBR surface the engine lights, so the albedo, roughness and normal views read it. Used by cliffRockTriplanar and mossyStoneTriplanar.