tlutdef(3G)							   tlutdef(3G)

NAME    [Toc]    [Back]

     tlutdef - defines a texture look-up table

C SPECIFICATION    [Toc]    [Back]

     void tlutdef(long index,
		  long nc,
		  long len,
		  unsigned long	*table,
		  long np,
		  float	*props)

PARAMETERS    [Toc]    [Back]

     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 TL_NULL.	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 TL_NULL.

DESCRIPTION    [Toc]    [Back]

     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.






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tlutdef(3G)							   tlutdef(3G)



     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 TV_MODULATE 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    [Toc]    [Back]

     afunction,	scrsubdivide, t, tevdef, tevbind, texbind, texdef2d, texgen

NOTES    [Toc]    [Back]

     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 getgdesc to determine whether texture
     mapping is	supported.

BUGS    [Toc]    [Back]

     tlutdef 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.


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