crow_keratin.shader

Everything the Old Crow is made of, on one surface. A bird is keratin throughout — the feather vane, the beak sheath, the scaled tarsus and the claw are one protein laid down three ways — so this shader carries all three patterns and pattern_mode (0 feather, 1 horn, 2 scale) picks the one standing on this material.

It hands the engine a PbrSurface, so the moon, the first light and the cliff's shadows reach the crow the way they reach the rock, and capture { pass = ... } reads real albedo, roughness and emissive off it.

Iridescence is in two halves. iridescence* drives the engine's thin-film lobe, broken up per vane so neighbouring feathers sit at different thicknesses and the hue crawls across the bird as it turns. sheen_glow adds the half a night scene needs — a view-dependent blue→violet→green wash on the grazing angles that does not wait for a light to be aimed at the bird. rim_* takes the same idea to the silhouette, because a black crow on black basalt has no edge otherwise.

wear greys the pigment and lifts roughness in broad blotches; on horn it also polishes the tip, which is what an old beak looks like.