n3f(3G)								       n3f(3G)

NAME    [Toc]    [Back]

     n3f - specifies a normal

C SPECIFICATION    [Toc]    [Back]

     void n3f(float vector[3])

PARAMETERS    [Toc]    [Back]

     vector   expects the address of an	array containing three floating	point
	      numbers.	These numbers are used to set the value	for the
	      current vertex normal.

DESCRIPTION    [Toc]    [Back]

     n3f specifies a floating point normal for lighting	calculations.  The
     normal becomes the	current	normal for subsequent vertices;	it is not
     necessary to respecify a normal if	it is unchanged	(e.g., a single	call
     to	n3f specifies normals for all vertices of a flat- shaded polygon).

     Vector components are Nx, Ny, and Nz for indices 0, 1, and	2.

     Lighting calculations assume that the specified normal is of unit length.
     If	non-unit-length	normals	are to be specified, use nmode (NNORMALIZE) to
     inform the	system that non-unit-length normals must be normalized.
     Lighting performance may be reduced in this event.

     When called with unequal arguments, scale causes the ModelView matrix to
     become non-orthonormal.  In this case, or in any other case that results
     in	a non-orthonormal ModelView matrix, normals are	also renormalized
     automatically by default, as specified by nmode (NAUTO).  Performance
     reduction,	if any,	matches	that of	nmode (NNORMALIZE).

SEE ALSO    [Toc]    [Back]

     lmbind, lmdef, nmode

BUGS    [Toc]    [Back]

     On	the IRIS-4D/120GTX and IRIS-4D/140GTX, there is	problem	with the
     graphics DMA hardware that	can cause data to be sent to the hardware
     after the subroutine call has returned.  If the data is modified
     immediately after the subroutine call, the	modified data may get sent
     down.  To avoid this, don't modify	the data until after another n,	v, or
     c call has	been made.

     This is an	example	of the bug:

	  vertex[2] = 1.0;
	  v3f(vertex);	 /* 4D/1x0 GTX hardware	may receive 3.0	for the	z value	*/
	  vertex[2] = 3.0;
	  v3f(vertex);


     This is one way to	work around the	problem:





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n3f(3G)								       n3f(3G)



	  vertexA[2] = 1.0;
	  v3f(vertexA);
	  vertexB[2] = 3.0;
	  v3f(vertexB);


									PPPPaaaaggggeeee 2222