Graphics Reference
In-Depth Information
Fig. 14.26 In this render, patches with a high amount of curvature are rendered as purple and blue ,
and small surface changes are yellow and green (Model and render courtesy of Rachel van de Meer)
14.4.8
Surface Tension
Surface tension is another way of saying that a surface tightly adheres to the shape
of the surface it is meant to represent. This is made possible by tangents that allow
the smooth interpolation of surface points across a surface. Surface tension is diffi -
cult to describe accurately with polygons because polygons are by nature rigid and
do not have any connections between faces. It can be imitated with polygons, but is
more time consuming than with NURBS. In NURBS, not only is it easier to repre-
sent, but using NURBS will sensitize any artist to surface tension. This will improve
the artist's observation skills and his ability to make a good likeness of a target
object, even when working in polygons.
Curvature can be rendered in some applications to identify problem areas in the
surface tension of patches. If the model is built well, colors that represent increases
or decreases in surface tension will cover large contiguous areas and blend smoothly
with each other (Fig. 14.26 ). Problems with curvature show up as small areas or
sharply different colors or jagged shapes.
Surface tension is important if your objects are meant to be convincing. If the
surface tension is duplicated correctly, the object will have more life to it than one
where this is not true. Poor surface tension will make a sail on a sailboat look like it
is made of rock instead of fabric swelled with wind, or the skin of a character look
like metal instead of a pliable organic substance. It might make metal look dented
where it should be smooth, or the elegant arc of a television screen look like the
bulge of a partly infl ated soap bubble. Surface tension can be described as an accurate
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