Transformation Operators - Essentials of Interactive Computer Graphics - page 191

Figure 8.11.

Reflecting a photograph across the y -axis.

Notice that the resulting rectangle formed by the scaled vertices is a mirror image
of the original rectangle. This fact can be observed by the mirrored photograph in
Figure 8.11. This mirror reflection can be generalized, where

( ,− )

S 1 1

mirror reflects vertices/objects across the x -axis, and

S ( − 1 , 1 )

mirror reflects vertices/objects across the y -axis.

Summary of the Scaling Operator

Order of operations. Once again, in general for all transformation operators,
the order of operations is important. In this case,

V a S

is different from

SV a .