Reference Talk:User Defined Pattern

copied from the povray.beta-test newsgroup:

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This version adds a new pigment pattern:

   pigment {
     user_defined {
       function { RED_FUNCTION },
       function { GREEN_FUNCTION },
       function { BLUE_FUNCTION },
       function { FILTER_FUNCTION },
       function { TRANSMIT_FUNCTION }
     }
   }

Each function is optional, in which case the corresponding component is set to 0. For example, the following sets the colour to rgbft <x,y,0,0,z>:

   pigment {
     user_defined {
       function { x },
       function { y },
       ,,
       function { z }
     }
   }

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The pattern is similar to `image_map` in that it directly specifies colours, rather than using a `colour_map` or `pigment_map`.