Phong Lighting

Phong Lighting

The Phong reflection model breaks lighting into three components:

1. Ambient — constant background illumination (prevents pure black shadows)
2. Diffuse — scattered light based on surface orientation toward light
3. Specular — mirror-like highlight based on the reflection direction

The Formula

color = ambient + diffuse + specular

Given:

• eyev: unit vector from surface toward camera
• normalv: unit normal vector of the surface
• lightv: unit vector from surface toward light

ambient = material.ambient

lightDotNormal = dot(lightv, normalv)
if (lightDotNormal < 0):
    diffuse = 0  // light is behind the surface
else:
    diffuse = material.diffuse * lightDotNormal

reflectv = reflect(-lightv, normalv)  // mirror direction
reflectDotEye = dot(reflectv, eyev)
if (reflectDotEye <= 0):
    specular = 0
else:
    factor = pow(reflectDotEye, material.shininess)
    specular = material.specular * factor

Reflect Formula

reflect(in, normal) = in - normal * 2 * dot(in, normal)

Test Cases from the Book

Using: color=(1,1,1), ambient=0.1, diffuse=0.9, specular=0.9, shininess=200

Your Task

Implement phong(eyex, eyey, eyez, nx, ny, nz, lx, ly, lz) that returns the combined lighting intensity.

Expected output:

1.9
0.1