** 3-D shaded surface with lighting. **

** SURFL(...) is the same as SURF (...) except that it draws the surface **

** with highlights from a light source. **

** **

** **

** SURFL(Z), SURFL(X,Y,Z), SURFL(Z,S), and SURFL(X,Y,Z,S) are all **

** legal. S, if specified, is the three vector S = [Sx,Sy,Sz] **

** that specifies the direction of the light source. S can also be **

** specified in spherical coordinates, S = [AZ,EL]. **

** **

** **

** The shading is based on a combination of diffuse, specular and **

** ambient lighting models. **

** **

** **

** The default value for S is 45 degrees counterclockwise from **

** the current view direction. Use CLA , HOLD ON, VIEW (AZ,EL), **

** SURFL(...), HOLD OFF to plot the lighted surface with view **

** direction (AZ,EL). **

** **

** **

** The relative contributions due to ambient light, diffuse **

** reflection, specular reflection, and the specular spread **

** coefficient can be set by using five arguments **

** SURFL(X,Y,Z,S,K) where K=[ka,kd,ks,spread]. **

** **

** **

** Relies on the ordering of points in the X,Y, and Z matrices **

** to define the inside and outside of parametric surfaces. **

** Try SURFL(X',Y',Z') if you don't like the results of **

** this function. Due to the way surface normal vectors are **

** computed, SURFL requires matrices that are at least 3-by-3. **

** **

** **

** See also SURF . **

** **