surface line() { color surface_color, layer_color; color layer_opac; float fuzz = 0.025; color green = color (0,0.5,0); point p1, p2; float half_width; float d; surface_color = Cs; layer_color = green; p1 = (0.25, 0.15, 0);/* endpoint #1 */ p2 = (0.85, 0.7, 0);/* endpoint #2 */ half_width = 0.05;/* 1/2 line width */ d = ptlined(p1, p2, (s, t, 0)); layer_opac = 1 - smoothstep(half_width - fuzz, half_width, d); surface_color = blend(surface_color, layer_color, layer_opac); Ci = surface_color; }