Refraction
The Refract command calculates the exit rays from selected incident rays at the intersection point with a boundary curve. The created exit rays remain selected. Pre-selection of incident rays is possible.

Options:
Direction: N1N2, N2N1
Trim ray curves: Yes / No
Extend ray curves: Yes / No
 

The direction (dir - command) of the curves defines how the ray travels i.e. how the curve will be refracted.

The exit rays are copies of the incident rays, which means they are on the same layer, have the same length and same properties.
 

The incident ray does not have to end at the boundary. The exit ray starts at the intersection point.
 

Attention, this also means, that the incident ray might be completely on the other side of the boundary curve.
 

If N1 is the index of refraction for air (~1.003) and N2 for glass (~1.48) then the add-in can calculate the refraction from air to glass with the left mouse button and from glass to air with the right mouse button.
 

Total internal reflection might take place if the incident light is traveling within the more optically dense medium towards the less optically dense medium. If the incident angle is larger than the critical angle the rays will be reflected.
 

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