Phong Lighting Model

Implement the basic Phong lighting model to simulate ambient, diffuse, and specular highlights on object surfaces.

Overview

• Compute lighting terms and shade a shape.

Learning Objectives

• Understand the basic components of the Phong lighting model: ambient, diffuse, and specular reflection.
• Learn how to calculate light vectors, view vectors, and reflection vectors in GLSL.
• Master the formulas for diffuse and specular reflection and the meaning of their parameters.
• Be able to implement a basic Phong lighting shader and observe the effects of adjusting parameters.

Prerequisites

• vector-math
• normal-vectors

Inputs

• vec2 u_resolution — Canvas size in pixels.
• float u_time — Time in seconds.

Key Concepts

• Diffuse lighting uses max(dot(n, l), 0.0).

float diff = max(dot(n, lightDir), 0.0);

• Specular highlights use pow (Phong/Blinn-Phong).

float spec = pow(max(dot(r, v), 0.0), shininess);

How To Implement (Step-by-step)

• Get normal n and a normalized light direction.
• Compute diffuse term with dot(n, l).
• Optionally compute specular with pow.
• Combine terms and output.

Self-check

• Does it compile without errors?
• Does the output match the goal?
• Are key values kept in [0,1]?

Common Mistakes

• Don’t use raw pixels without normalization.