light_source(3G)

NAME

light_source − define light source positions and colors

SYNOPSIS

C Syntax:

void light_source(fildes,index,type,red,green,blue,x,y,z);
int fildes,index,type;
float red,green,blue,x,y,z;

FORTRAN77 Syntax:

subroutine light_source(fildes,index,type,red,green,blue,x,y,z)
integer*4 fildes,index,type
real red,green,blue,x,y,z

Pascal Syntax:

procedure light_source(fildes,index,type:integer; red,green,blue,x,y,z:real);

DESCRIPTION

Input Parameters

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

index Selects the light source to be modified. The total number of light sources is device-dependent.

type Selects the light source type from DIRECTIONAL, POSITIONAL

red,green,blue Values (in the range 0.0 to 1.0) that define the color of the light source.

x,y,z x,y,z coordinate position of the light source or a vector pointing to the light source. Note that if this is a vector, it does not need to be normalized to unit length.

Discussion

Light_source specifies the location and color of different light sources which are then used in shading of filled polygons. Up to eight (8) different light sources can be specified on a HP98721 device, and up to fifteen (15) on all other 3-D accelerated devices. These numbers do not include the ambient light source which is always index 0 and cannot be modified to a DIRECTIONAL or POSITIONAL type.

The type parameter can be one of the following:

DIRECTIONAL Point source at infinity. The x,y,z parameters specify a vector anchored at the origin and directed toward the light source.

POSITIONAL Point source close to viewing area. The x,y,z parameters specify the position of the light source in world coordinates.

Additional aspects of POSITIONAL light sources can be set with light_model .

DEFAULTS

DIRECTIONAL directed at x=0.0, y=0.0, z=−1.0 with red=1.0, green=1.0, blue=1.0

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