FragmentShader

Colour every pixel of your shader your own way, then light it like the rest of the scene with one call.

The fragment stage of a Shader: write an out vec4, in display colour. glueShade(albedo, pos, normal) lights a surface like a Part, with sun, sky and lights, and the Shader's attributes arrive as uniforms of the same name. Blending is off, so a fragment can't fade: dissolve it with discard. In Rendered it draws over the traced picture, hidden where parts are in front; a Traced Shader leaves this stage out.