/[gzz]/gzz/Documentation/Manuscripts/Irregu/irregu.tex
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revision 1.113 by tjl, Sat Nov 30 15:26:52 2002 UTC revision 1.114 by tjl, Sat Nov 30 17:55:34 2002 UTC
# Line 579  solid shapes. Line 579  solid shapes.
579    
580  \subsection{Drawing the shape}  \subsection{Drawing the shape}
581    
582    \label{secshape}
583    
584  XXX figs for all these shapes!  XXX figs for all these shapes!
585    
586  The type of offsetting in Eq.(\ref{eqoffset}) is implemented  The type of offsetting in Eq.(\ref{eqoffset}) is implemented
# Line 723  good quality. In this section, we presen Line 725  good quality. In this section, we presen
725  able to approximate the shape well in a single pass.  able to approximate the shape well in a single pass.
726    
727  The algorithm works by precalculating the displacement or offset  The algorithm works by precalculating the displacement or offset
728  of the outer edge of the black line, assuming that the shape algorithm  of the outer edge of the black line, assuming that the inner
729  draws the inner edge.  edge is defined as the edge of the area drawn by the
730  The precalculated edge shapes are different for different orientations,  algorithms of Section~\ref{secshape}.
731  but this can be approximated by storing the offsets at a discrete set  The precalculated edge shapes are different
732    for different angles,
733    but can be approximated by storing the offsets at a discrete set
734  of orientations in different components of a texture and interpolating  of orientations in different components of a texture and interpolating
735  by calculating dot products.  by calculating dot products.
736  This approximation is not completely free of artifacts (FIG),  This approximation is not completely free of artifacts (FIG),
# Line 734  but is sometimes acceptable and is fast Line 738  but is sometimes acceptable and is fast
738    
739  Non-photorealistic line width scaling can be obtained by computing  Non-photorealistic line width scaling can be obtained by computing
740  each mip-map\cite{williams83pyramidal}  each mip-map\cite{williams83pyramidal}
741  level of the outer surface textures separately  level of the outer edge textures separately
742  with the desired line width for that scale.  with the desired line width for that scale.
743  This method of computing mip-maps is similar to the art maps used in  This method of computing mip-maps is similar to the art maps used in
744  \cite{klein00nonphotorealistic}.  \cite{klein00nonphotorealistic}.
745  Because the textures store displacement values,  Because the textures store offset/displacement values,
746  the mip-map levels interpolate seamlessly.  the mip-map levels interpolate seamlessly.
747  However, zooming above the highest level of detail in the mip-map  However, zooming above the highest level of detail in the mip-map
748  will fall back to the linear scaling.  will fall back to the linear scaling.
# Line 762  to extract the discontinuities. Line 766  to extract the discontinuities.
766    
767  The advantage of image-space algorithms is that their performance  The advantage of image-space algorithms is that their performance
768  does not depend on the complexity of a scene; however, it appears  does not depend on the complexity of a scene; however, it appears
769  that NV30/R300 generation of graphics chips is flexible enough  that only the NV30/R300 generation of graphics chips is flexible enough
770  to support image-based operations well, due to the number of texture  to support image-based operations well, due to the number of texture
771  accesses and floating point operations needed. Also, it is more  accesses and floating point operations needed. Also, it is more
772  difficult (although possible)  difficult (although possible)

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