SECTION 4.6
323
Patterns
mapped. If more than one point (u,
v)
in parameter space is mapped to the same
point in device space, the point selected is the one with the largest value of
v.
If
multiple points have the same
v,
the one with the largest value of
u
is selected. If
one patch overlaps another, the patch that appears later in the data stream paints
over the earlier one.
Note also that the patch is a control surface rather than a painting geometry. The
outline of a projected square (that is, the painted area) might not be the same as
the patch boundary if, for example, the patch folds over on itself, as shown in
Appearance
Painted area
Patch boundary
FIGURE 4.21
Painted area and boundary of a Coons patch
addition to those common to all shading dictionaries (Table 4.28) and stream dic-
tionaries (Table 3.4 on page 62).