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162 7. The Rendering Pipeline
– For a directional light source with incident direction
ˆ
d:
I
d
= −
ˆ
d · ˆn.
– For a spotlight located at P
l
, pointing in direction
ˆ
d and having
light cone angles
1
and
2
:
I
d
=
⎧
⎪
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎪
⎩
P
l
− p
|P
l
− p|
· ˆn if <
1
,
P
l
− p
|P
l
− p|
· ˆn
1 −
(
−
1
)
(
2
−
1
)
if
1
≤ ≤
2
,
0if
2
< ,
where
is the angle between the direction of the incident light
and the surface normal, and is given by
= cos
−1
(
ˆ
d · (p −P
l
)).
Diffuse lighting is the most significant component of an illumination
model, and if there is more than one light source in the scene, the
intensity of the diffuse reflection component is summed over all the
light sources.
• Specular reflection (I
s
)