One-parameter shader

float shading = chf('shading');
vector color = chv('color');

vector pos_light = {2.6, 1.2, 0.6};
vector dir = normalize(pos_light - v@P);

float lumen = max(1.0 - shading, 0.0);
float angle = max(dot(dir, v@N), lumen);
shading = fit(shading, 1, 2, 1, 20);
float shade = pow(angle, max(shading, 1.0));

v@Cd = color * shade;