                        [Images & Graphics Header]

                   Extensions of the Neutral File Format

                               April 16, 1993

Positional Light

Description:
"l" X Y Z I R G B
Format:
l %g %g %g %g %g %g %g
A light is now defined by it's XYZ position, intensity and color. Intensity
is a value between 0 and 1 and color is defined as RGB with values between
0 and 1 like bachground color.

Fill color and shading parameters

Description:
"f" red green blue Kd Ks Shine T index_of_refraction Ka
Format:
f %g %g %g %g %g %g %g %g %g
A ambient component Ka was added to the original description of fill color
and shading parameters. Ka should be between 0 and 0.3, the default value
is 0.2.

Bezier patch

Description:
"pb" u_degree v_degree
x00 y00 z00
x10 y10 z10
..
xmn ymn zmn    // m==u_degree; m==v_degree

Format:
pb %d %d
%g %g %g
..
%g %g %g

u_dgree and v_degree are the degrees of the Bezier patch in direction of
parameters u and v. The description of the degrees is followed by the
coordinates of the Bezier points. A Bezier patch is described by
(u_degree+1)*(v_degree+1) points. The Bezier points are listed in columnwise
order with u as line index and v as column index.

NURBS

Description:
"pn"
u_degree v_degree u_count v_count u_points v_points
u1 u2 ... u_u_points
v1 v2 ... v_v_points
x1 y1 z1 w1
..
xr vr wr zr            // r = u_points * v_points
[description of trimming curves]
"pn_end"


Format:
pn
%d %d %d %d %d %d
%g %g .. %g
%g %g .. %g
%g %g %g %g
..
%g %g &g &g
[description of trimming curves]
pn_end

In the first line of a description of a non-uniform rational B-Spline patch
the degree, the dimension of knot vectors and the number of control points
in direction of parameter u and v are listed. This is followed by the listing
of knot vectors, first in direction of u, then in direction of v. After that
the control points (deBoor points) of the patch are listed. The deBoor points
are described in homogeneous coordinates with the weight w as it's fourth
component. The points have to be listed in linewise order with u as line index
and v as column index.

There is another kind of NURBS: "nonrational" NURBS. These have the same
description as listed before, only with a new descriptor: "pnn" and without
the weights "w..." in the control points.

It is possible to list any number of trimming curves for a NURBS patch
immediately after the description of the patch.

Description of a trimming curve:
t_ord t_count t_points
t1 t2 .. t_t_count
x1 y1 z1 w1
..
xr yr zr wr        // r=t_points

Format:
%d %d %d
%g %g .. %g
%g %g %g %g
..
%g %g %g %g

t_ord is the order of the trimming curve, t_count is the dimension of the knot
vector and t_points is the number of control points. The control points are
listed after the description of the knot vector.

The whole description of a NURBS patch including trimming curves has to be
completed by the string "pn_end".

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