Game Development Reference
In-Depth Information
Gouraud shading's strength and weakness lies in its interpolation. If a polygon
covers more pixels on the screen space than the number of vertices it has, the
interpolating color values from samples of expensive lighting calculations at vertices
is less processor-intensive than performing the lighting calculation for each pixel.
However, effects such as specular highlights might not be rendered correctly. The
following diagram explains Gouraud shading:
Gouraud Shading
Let's now summarize the steps:
1. Determine the normal at each polygon vertex
2. Apply an illumination model (Lambertian, Blinn-Phong) to each vertex to
calculate the vertex intensity
3.
Linearly interpolate the vertex intensities over the surface polygon
Phong shading
Phong shading interpolates surface normals across rasterized polygons and
computes pixel colors based on the interpolated normals and a reflection model.
The Phong interpolation method works better than Gouraud shading when applied
to a reflection model that has small specular highlights such as the Phong reflection
model. The following diagram explains Phong shading:
Phong Shading
