Question

Q1: Draw the graphics pipeline?

Q2: Differentiate between Phong and Modified Phong model?

Answer 1

1-ans-

2-ans-

The Phong model computes the specular response as the dot product between the mirror reflection direction and the viewing direction, raised to a power.

For example, if V⃗ V→ is the viewing direction, L⃗ L→ the incoming light direction and R⃗ R→ the perfect specular reflection direction for L⃗ L→, then the specular response is max(V⃗ .R⃗ ,0)pmax(V→.R→,0)p, where pp is the exponent that controls the fall-off of the specular response.

The Modified-Phong model uses a half vector H⃗ H→, which is computed as H⃗ =L⃗ +V⃗ |L⃗ +V⃗ |H→=L→+V→|L→+V→|, which is then used to compute the specular response as max(H⃗ .N⃗ ,0)pmax(H→.N→,0)p, where N⃗ N→ is the surface normal. The idea is that when the eye vector V⃗ V→ is aligned perfectly with the perfect mirror direction R⃗ R→, the half vector H⃗ H→ would be exactly aligned with the surface normal N⃗ N→. Hence the Blinn-Phong can get away with computing an expensive mirror direction R⃗ R→ everytime by using the half vector which can model the specular response.

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