Toon Shading

Implement a non-photorealistic rendering technique that simulates the visual style of cartoons or comic books by quantizing light intensity into discrete color levels, often combined with edge detection.

Overview

• Compute lighting terms and shade a shape.

Learning Objectives

• Understand the basic principles of toon shading: discretization of lighting.
• Learn how to use step() or floor() functions to map continuous light intensity to a limited number of color levels.
• Master basic edge detection methods (e.g., based on the dot product of normal and view direction) and their application in toon shading.
• Be able to implement a toon shader with hard shadows and outlines.
• Explore how to change the style of toon rendering by adjusting the number of color levels and colors.

Prerequisites

• phong-lighting
• step-function
• edge-detection-techniques

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

• Clamp t into [0,1] when needed.
• Don’t use raw pixels without normalization.
• Make sure edge0 < edge1 for smoothstep().