Phong Lighting Model

Three Components of Surface Lighting

In 1975, Bui Tuong Phong published a model that broke real-time lighting into three terms. It is empirical, not physically based, but fast and convincing enough to dominate games for three decades before PBR took over.

Ambient: constant indirect light so surfaces are never pure black
Diffuse (Lambertian): max(0, N dot L) where N is surface normal, L is light direction
Specular: shiny highlight toward the viewer

Blinn-Phong Variant

The Blinn-Phong specular term uses a half-angle vector instead of a reflection vector:

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For example, a surface with normal (0,0,1), light at (2,2,5), and eye at (0,0,5) produces a bright specular lobe when N dot H is near 1. Diffuse depends only on light angle; specular depends on both light and view angles.

Ambient: material ambient * light color
Diffuse: matte scatter, no view dependence
Specular: shininess controls highlight tightness (32 is moderately glossy)

For This Exercise

You will implement Blinn-Phong lighting for a single surface point with given normal, light position, eye position, and material constants. This task asks you to compute L, V, H, and print the final RGB color. Even PBR renderers retain the same N dot L diffuse structure introduced here.

Write a C program that implements the Blinn-Phong lighting model for a single point on a surface.

Requirements:

Define a surface point at origin (0, 0, 0) with normal N = (0, 0, 1)
Define a point light at position L_pos = (2, 2, 5) with color (1.0, 1.0, 1.0)
Define the camera/eye at E = (0, 0, 5)
Material properties: ambient = (0.1, 0.1, 0.1), diffuse = (0.7, 0.2, 0.2), specular = (0.8, 0.8, 0.8), shininess = 32
Compute:
- Light direction L = normalize(L_pos - surface_point)
- View direction V = normalize(E - surface_point)
- Half-angle H = normalize(L + V)
- Ambient = material.ambient * light.color
- Diffuse = material.diffuse * light.color * max(0, N dot L)
- Specular = material.specular * light.color * pow(max(0, N dot H), shininess)
- Final = Ambient + Diffuse + Specular
Print each component (ambient, diffuse, specular) as RGB values
Print the final color
Test with three shininess values: 8, 32, 128, showing how the specular highlight tightens
Implement vector helpers: dot, normalize, add, subtract
Use 3 decimal places for output

Three Components of Surface Lighting

Ambient: constant indirect light so surfaces are never pure black
Diffuse (Lambertian): max(0, N dot L) where N is surface normal, L is light direction
Specular: shiny highlight toward the viewer

Blinn-Phong Variant

The Blinn-Phong specular term uses a half-angle vector instead of a reflection vector:

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Ambient: material ambient * light color
Diffuse: matte scatter, no view dependence
Specular: shininess controls highlight tightness (32 is moderately glossy)

For This Exercise

Write a C program that implements the Blinn-Phong lighting model for a single point on a surface.

Requirements:

Define a surface point at origin (0, 0, 0) with normal N = (0, 0, 1)
Define a point light at position L_pos = (2, 2, 5) with color (1.0, 1.0, 1.0)
Define the camera/eye at E = (0, 0, 5)
Material properties: ambient = (0.1, 0.1, 0.1), diffuse = (0.7, 0.2, 0.2), specular = (0.8, 0.8, 0.8), shininess = 32
Compute:
- Light direction L = normalize(L_pos - surface_point)
- View direction V = normalize(E - surface_point)
- Half-angle H = normalize(L + V)
- Ambient = material.ambient * light.color
- Diffuse = material.diffuse * light.color * max(0, N dot L)
- Specular = material.specular * light.color * pow(max(0, N dot H), shininess)
- Final = Ambient + Diffuse + Specular
Print each component (ambient, diffuse, specular) as RGB values
Print the final color
Test with three shininess values: 8, 32, 128, showing how the specular highlight tightens
Implement vector helpers: dot, normalize, add, subtract
Use 3 decimal places for output

Topic Overview

Three Components of Surface Lighting

Blinn-Phong Variant

For This Exercise

Implementation Task

Progressive Hints

Resources

Open Source

Phong Lighting Model

Topic Overview

Three Components of Surface Lighting

Blinn-Phong Variant

For This Exercise

Implementation Task

Progressive Hints

Resources

Open Source