Controlling the size and sharpness of a specular highlight comes down to this line:
Let's break it down.
What shininess does
shininess is the exponent passed to pow — it controls how tight and sharp the highlight appears:
shininess = 4→ large, soft highlight (matte rubber)shininess = 16→ medium, like plasticshininess = 64→ small, sharp (metallic paint)shininess = 256→ tiny pinpoint (mirror or glass)
A larger exponent means only pixels very close to the perfect reflection angle keep any brightness — the bright spot shrinks and concentrates.
What the half-vector hV is
This tutorial uses the Blinn-Phong approach instead of computing a full reflection vector. The half-vector sits midway between the light direction l and the view direction v:
Add the two directions together and normalize. Then check how well the surface normal n aligns with hV — better alignment means a brighter highlight.
Blinn-Phong is cheaper to compute than classic Phong and behaves more stably when the viewer is at a grazing angle.
Try changing it
| Change | Effect |
|---|---|
shininess = 16.0 to 4.0 | Large, soft highlight — rubber-like surface |
shininess = 16.0 to 64.0 | Small, tight highlight — smooth surface |
Change 0.6 in * spec * 0.6 to 1.5 | Brighter specular, may clip to white |
Exercise
The exercise has spec = 0.0 and no visible highlight. Fill in the TODO to compute the specular value using hV and shininess.
Answer Breakdown
Starting state: spec = 0.0 — the sphere shows only diffuse shading.
The fix: compute dot(n, hV) to measure how well the normal aligns with the half-vector, then raise it to shininess to concentrate the result into a tight highlight. shininess = 16.0 gives a medium-smooth plastic appearance.
Try changing shininess to 2.0 and see how far the highlight spreads across the sphere.