
20.7 Sphere Maps 927
A sphere of radius 1 and centered at the view-space origin (0, 0, 0) is shown
in Figure 20.18 (b). Also shown is the reflection vector r and the normal vector h.
The direction vector for view space is (0, 0, 1). The figure shows the negation of
this positioned at the reflected vector on the sphere. The nor mal vector is projected
onto the image plane (the vertical blue line segment); the orange line segment is
the direction of projection. The black endpoint of the orange segment shown on the
image plane gives you a pair (x, y), which is the texture coordinate assigned to the
position P of the original object.
The view-space normal