Graphics Reference
In-Depth Information
Inline Exercise 15.5:
Mandatory; do not continue until you have done this:
Draw a schematic diagram of this scene from three viewpoints.
1. The orthographic view from infinity facing along the
x
-axis. Make
z
increase to the right and
y
increase upward. Show the camera and its
field of view.
2. The orthographic view from infinity facing along the
y
-axis. Make
x
increase to the right and
z
increase downward. Show the camera and its
field of view. Draw the vertex normals.
3. The perspective view from the camera, facing along the
−
−
z
-axis; the
camera should not appear in this image.
We begin the ray-casting renderer by expanding and implementing our initial
pseudocode from Listing 15.2. It is repeated in Listing 15.11 with more detail.
Listing 15.11: Detailed pseudocode for a ray-casting renderer.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
for each pixel row
y
:
for each pixel column
x
:
let
R
= ray through screen space position
(
x
+
0
.
5,
y
+
0
.
5
)
closest
=
∞
for each triangle
T
:
d
= intersect(
T
,
R
)
if (
d
<
closest
)
closest
=
d
sum
=0
let
P
be the intersection point
for each direction
v
i
:
sum
+= light scattered at
P
from
v
i
to
v
o
image
[
x
,
y
]=
sum
The three loops iterate over every ray and triangle combination. The body of
the for-each-triangle loop verifies that the new intersection is closer than previous
observed ones, and then shades the intersection. We will abstract the operation of
ray intersection and sampling into a helper function called
sampleRayTriangle
.
Listing 15.12 gives the interface for this helper function.
Listing 15.12: Interface for a function that performs ray-triangle
intersection and shading.
1
2
3
bool
sampleRayTriangle(
const
Scene
& scene,
int
x,
int
y,
const
Ray
&R,
const
Triangle
&T,
Radiance3
& radiance,
float
& distance);
The specification for
sampleRayTriangle
is as follows. It tests a particular
ray against a triangle. If the intersection exists and is closer than all previously
observed intersections for this ray, it computes the radiance scattered toward the
viewer and returns
true
. The innermost loop therefore sets the value of pixel
(
x
,
y
)
