trail.shader

Shades the ribbon a TrailRenderer builds.

The ribbon carries its gradient in the vertex colour — colour and opacity interpolated from the head to the tail as the strip is built — so this shader brings that through and lets base_color, a base-colour texture and an emissive texture ride along it.

Unlit, by two arguments: a trail is usually its own light source, and lighting a surface with no thickness puts a shading seam down its middle where the two sides disagree about which way they face.