Figure 6

Texture mapping onto the curved surfaces of tube and ribbon segments. (A) The local coordinate frames needed for drawing a single amino acid as a tube or ribbon segment are shown using the same conventions as in Figure 3, except that a small blue sphere marks the amino-terminal end of the segment, while a small red sphere marks the carboxyl-terminal end. The same amino acid is drawn as a tube segment in (B) and as a ribbon segment in (C). In both (B) and (C), a blue end cap indicates the amino-terminus of the segment, while a red end cap indicates the carboxyl-terminus. (D) This two-dimensional swirl image was mapped onto the curved three-dimensional surfaces of the tube (B) and ribbon (C) segments by using (s, t) texture coordinates that are assigned to each vertex of a segment when its geometry is first calculated.