Shading Types

Flat Shading

• One colour per triangle
• Normal is constant across the triangle
• Compute lighting once per triangle
• Fast but shows faceted surfaces

Gouraud Shading (Smooth Shading)

• Lighting computed at each vertex
• Colours interpolated across the triangle using barycentric coordinates
• Smooth appearance but may miss highlights inside large triangles

Phong Shading (Per-Pixel Shading)

• Normal vectors interpolated across the triangle
• Lighting equation evaluated per pixel (fragment)
• Most accurate of the three
• Computationally more expensive

Comparison

Method	Lighting Computed	Quality
Flat	Per triangle	Faceted
Gouraud	Per vertex	Smooth but may miss highlights
Phong	Per pixel	Best quality

Summary

• Flat: one colour per triangle
• Gouraud: interpolate vertex colours
• Phong: interpolate normals, compute lighting per pixel

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Past Paper Questions

2023 Paper 3 Question 4: Compare flat, Gouraud, and Phong shading. When might each be appropriate?