Shading Models

How does a surface respond to light? Shading model.

Flat shading:

• One color per triangle.
• Fast, low quality.
• Looks faceted.

Gouraud shading:

• Compute color at each vertex.
• Interpolate across triangle.
• Smooth gradients but misses specular highlights.

Phong shading:

• Interpolate the normal across triangle.
• Compute color per pixel.
• Better specular.
• Slower.

Phong reflection model (different from Phong shading):

• ambient + diffuse + specular.

Blinn-Phong:

• Uses half-vector instead of reflection.
• Faster, similar appearance.

Lambertian (just diffuse):

• diffuse only.
• Looks matte. Good for chalk, paper, fabric.

PBR (Physically Based Rendering):

• Modern AAA standard.
• Material parameters: roughness, metallic, baseColor, normal.
• Cook-Torrance BRDF.
• Energy conservation.
• Realistic appearance across lighting.

PBR feels real. Used in Unreal, Unity HDRP, Blender, films.

For toy: Phong is enough. PBR is the production target.