surface_coefficients(3G)

NAME

surface_coefficients, bf_surface_coefficients − select the ambient, diffuse and specular coefficients for filled area primitives, and back-facing elements of filled area primitives

SYNOPSIS

C Syntax:

void surface_coefficients ( fildes, ka, kd, ks );
int fildes;
float ka, kd, ks;

void bf_surface_coefficients ( fildes, ka, kd, ks );
int fildes;
float ka, kd, ks;

FORTRAN77 Syntax:

subroutine surface_coefficients ( fildes, ka, kd, ks )
integer*4 fildes
real ka, kd, ks

subroutine bf_surface_coefficients ( fildes, ka, kd, ks )
integer*4 fildes
real ka, kd, ks

Pascal Syntax:

procedure surface_coefficients ( fildes:integer;
ka, kd, ks:real );

procedure bf_surface_coefficients ( fildes:integer; ka,
kd, ks:real );

DESCRIPTION

Input Parameters

fildes Integer file descriptor returned by gopen when an I/O path to a graphics device is opened.

ka Coefficient of ambient reflection

kd Coefficient of diffuse reflection

ks Coefficient of specular reflection

Discussion

The surface_coefficients subroutine specifies ambient, diffuse, and specular lighting constants for polygonal surfaces. bf_surface_coefficients specifies the same constants for back-facing shaded polygons. Its parameters are used to determine the intensity of back-facing shaded polygons. The use of surface coefficients on front-facing and back-facing polygons is initiated by a call to shade_mode, turning shading on and to bf_control, turning on special handling for back-facing polygons.

The reflection coefficients defined here are multiplied by each of these terms and are used as a means to attenuate the contribution of various components. When shading polygons, the basic light source computations consist of the sum of three separate components:

The energy due to ambient illumination:

Ea = (ka)(Rs)(Ia)

The energy due to diffuse reflection from a point source, where n is device-dependent (see discussion in light_switch(3G) on the number of lights supported):

Ed = (kd)n∑j=1(Rs)(Ipj)(cos(ij))

The energy due to specular reflection from a point source, where n is device-dependent (see discussion in light_switch(3G) on the number of lights supported):

Es = (ks)n∑j=1(W)(Ipj)((cos(sj))h)

Where:

Rs	=	Reflectance coefficient of the surface
		(RGB color set by fill_color)
Ia	=	Ambient illumination
		(RGB color set by light_ambient)
Ip	=	Point source illumination
		(RGB color set by light_source)

ka	=	Coefficient of ambient reflection
kd	=	Coefficient of diffuse reflection
ks	=	Coefficient of specular reflection

i	=	Incident angle of light source
W	=	Specular reflection coefficient (red, green,
		blue color set by surface_model)
s	=	Angle between viewpoint ray and reflected ray.
h	=	Specular highlight power is degree of
		shininess (highlight)

DEFAULTS

ka = 1.0 kd = 1.0 ks = 1.0

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