The RenderMan Interface - Paul Bourke

Appendix E
STANDARD BUILT-IN FILTERS
In this section the required RenderMan Interface filters are defined. Keep in mind that the
filter implementations may assume that they will never be passed (x, y) values that are
outside the ([−xwidth/2, xwidth/2], [−ywidth/2, ywidth/2]) range.
E.1 Box Filter
RtFloat
RiBoxFilter (RtFloat x, RtFloat y, RtFloat xwidth, RtFloat ywidth)
{
return 1.0;
}
E.2 Triangle Filter
RtFloat
RiTriangleFilter (RtFloat x, RtFloat y, RtFloat xwidth, RtFloat ywidth)
{
return ( (1.0 – fabs(x)) / (xwidth*0.5) )
* ( (1.0 – fabs(y)) / (ywidth*0.5) ) ;
}
E.3 CatmullRom Filter
RtFloat
RiCatmullRomFilter (RtFloat x, RtFloat y, RtFloat xwidth, RtFloat ywidth)
{
RtFloat r2 = (x*x + y*y);
RtFloat r = sqrt(r2);
return (r >= 2.0) 0.0 :
(r < 1.0) (3.0*r*r2 – 5.0*r2 + 2.0) : (–r*r2 + 5.0*r2 – 8.0*r + 4.0);
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