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152 Chapter 17: Rendering
sometimes give unexpected results. Usually there
is a workaround for the problem, or more than
one. This topic describes some situations that can
arise, and ways to correct them.
Par a ll el Pr ojecti on Los es Det ai l
Iftheprojectioncageissetupsoprojectedraysrun
parallel to part of the high-resolution geometry,
that portion of geometry c an b e lost in the normal
bump map.
Forexample,inthisscene,thenormalbumpmap
isbasedonahigh-resolutioncylinderthathas
indentations at the top and bottom.
Default cage around high-res cylinder
However, the normal bump map does not show
the end indentations.
Indentation is missing from top and bottom of the cylinder’s
normal bump map.
Thereasonisthatwiththedefaultprojectioncage,
theraysparallelthesidesoftheindentation,and
so details are lost.
Projection rays (shown in red) pa rallel the sides of the
indentation.
To correct the problem, you can move the end of
the cage upward, and scale it inward a little, so the
raysdon’trunsonearlyparalleltothesideofthe
indentation.