CS 435 Autumn 1997 --- Introduction to Interactive Graphics

Implementing Phong Specular Illumination

Phong Specular Illumination Formula for Intensity (from class notes, pg. 8-12)

da=I_ak_a + I_pk_d (N · L )
I=d_a + (1-d_a)I_pk_s (N · H)ⁿ
Add specular if N · L > 0 and N · H > 0

Object Color and Illumination

Now we need to add color into this intensity calculation. The diffuse and ambient intensity is multiplied by the color of the object. Specular illumination is affected by the color of the light, not the object in the simple model. (The color of the light actually affects all components.)

	n_l = (N · L)
	if (n_l > =0.0)
	   da = obj_amb[obj] + obj_kd[obj]*n_l
	else 
	   da = obj_amb[obj] 
	d_a.r = da*obj_color[obj].r
	d_a.g = da*obj_color[obj].g
	d_a.b = da*obj_color[obj].b
                   spec.r=spec.g=spec.b=0;
	if (n_l > 0)
	{
	   n_h = pow(MAX(0, (N · H)), obj_specexp[obj])
	   spec.r  = obj_ks[obj]*n_h
	   spec.g  = obj_ks[obj]*n_h
	   spec.b  = obj_ks[obj]*n_h
	}
	final_color.r = MIN(1.0, (d_a.r + (1-d_a.r)*spec.r))
	final_color.g = MIN(1.0, (d_a.g + (1-d_a.g)*spec.g))
	final_color.b = MIN(1.0, (d_a.b + (1-d_a.b)*spec.b))

Faceted Shading:

Create a structure to hold the user selected color of each object (obj_color[obj])
Create a structure to hold the final color after illumination of each polygon (face_color[obj][face] ) Set face_color[obj][face]= final_color.

Examples of illumination types

Ambient Illumination	Diffuse plus Ambient Illumination	Specular plus Diffuse plus Ambient Illumination

David S. Ebert
Sun Nov 16 01 11:19:09 EST 1997