tltdef(3G)

NAME
     tltdef - defines a texture look-up table

FORTRAN SPECIFICATION
     subroutine tltdef(index, nc, len, table, np, props)
     integer*4 index, len, nc, np
     integer*4 table(*)
     real props(np)

PARAMETERS
     index   expects the name of the texture look-up table being defined.
             Index 0 is reserved as a null definition, and cannot be
             redefined.

     nc      expects the number of components per table entry.

     len     expects the length of table in table entries.

     table   expects a long-word aligned array of packed nc, 8-bit, component
             table entries.

     np      expects the number of symbols and floating point values in props,
             including the termination symbol TLNULL.  If np is zero, it is
             ignored.  Operation over network connections is more efficient
             when np is correctly specified, however.

     props   expects the array of floating point symbols and values that
             define the texture look-up table.  props must contain a sequence
             of symbols, each followed by the appropriate number of floating
             point values.  The last symbol must be TLNULL.

DESCRIPTION
     Texture coordinates, s,t,r may be specified at geometry vertices,
     similarly to color, depth, and vertex normals.  The texture coordinates
     are interpolated from the values specified at the vertices for each
     screen pixel touched by the geometry.  A texture function maps the
     texture coordinates s,t, or s,t,r, corresponding to a screen pixel into
     nc values, called texture function outputs, using an image and a set of
     properties. The texture function outputs may be translated with a texture
     look-up table.  The texture lookup outputs are used by the texture
     environment function to modify the screen pixel color.

     The texture look-up table is defined by tlutdef and selected by tlutbind.
     texdef2d and texdef3d define a texture function and texbind selects which
     texture function definition to use.  The texture environment function is
     defined by tevdef and selected by tevbind. The texture coordinates are
     specified with the t family of commands.

     The texture look-up table allows the texture function outputs to be
     translated via the texture look-up table. The interaction between texture
     look up tables and textures with differing number of components is as
     follows:
          tlut nc    texture nc    action
          -------    ----------    -------------
          2          1             I looks up I,A
                     2             I,A looks up I,A
                     3             R,G,B passes through unchanged
                     4             R,G,B,A passes through unchanged

          3          1             I looks up R,G,B
                     2             I,A passes through unchanged
                     3             R,G,B looks up R,G,B
                     4             R,G,B,A passes through unchanged

          4          1             I looks up R,G,B,A
                     2             I looks up R,G,B; A looks up A.
                     3             R,G,B,B looks up R,G,B,A
                     4             R,G,B,A looks up R,G,B,A


     If the tlutdef parameter nc is not equal to the texdef parameter nc,
     tlutdef's nc determines which texture environment equation is used.  For
     example, if tlutdef's nc is 2 and a 1-component texture is used, texture
     environment TVMODU will scale red, green, and blue by lookup output I and
     alpha by lookup output A.

     There are no properties currently defined for this command. Different
     sized components may be supported in the future.

SEE ALSO
     afunct, scrsub, t, tevbin, tevdef, texbin, texdef, texgen

NOTES
     IRIS-4D G, GT, GTX, VGX, VGXT models, and the Personal Iris, Iris Indy,
     and Iris Indigo, do not support texture look up tables.  tlutdef is
     ignored by these machines.  Use getgde to determine whether texture
     mapping is supported.

BUGS
     tltdef is not supported on Impact.

     On Infinite Reality one and three component texture images on Infinite
     reality always return the 255th entry in the alpha table for two and four
     component tluts.