2003-2004
Silicon Graphics, Inc.
glLightModel
3G
glLightModel
glLightModelf
glLightModelx
glLightModelfv
glLightModelxv
set the lighting model parameters
C Specification
void glLightModelf
GLenum pname
GLfloat param
void glLightModelx
GLenum pname
GLfixed param
Parameters
pname
Specifies a single-valued lighting model parameter. Must be
GL_LIGHT_MODEL_TWO_SIDE.
param
Specifies the value that param
will be set to.
C Specification
void glLightModelfv
GLenum pname
const GLfloat * params
void glLightModelxv
GLenum pname
const GLfixed * params
Parameters
pname
Specifies a lighting model parameter.
GL_LIGHT_MODEL_AMBIENT and
GL_LIGHT_MODEL_TWO_SIDE are accepted.
params
Specifies a pointer to the value or values that
params will be set to.
Description
glLightModel sets the lighting model parameter.
pname names a parameter and
params
gives the new value. There are two lighting model parameters:
GL_LIGHT_MODEL_AMBIENT
params
contains four fixed-point or floating-point values that
specify the ambient intensity of the entire scene.
The values are not clamped. The initial value is
(0.2, 0.2, 0.2, 1.0).
GL_LIGHT_MODEL_TWO_SIDE
params
is a single fixed-point or floating-point value that
specifies whether one- or two-sided lighting calculations
are done for polygons. It has no effect on the lighting
calculations for points or lines. If
params
is 0, one-sided lighting is specified, and both front- and
back-facing polygons are assigned the same computed color.
Otherwise, two-sided lighting is specified. In this case,
vertices of back-facing polygons have their normals reversed
before the lighting equation is evaluated. Vertices of
front-facing polygons are always lighted with no change to
their normals. The initial value is 0. Note that there is
only one set of material properties shared by both
front- and back-facing polygons.
The lighted color of a vertex is the sum of the material
emission intensity, the product of the material ambient
reflectance and the lighting model full-scene ambient
intensity, and the contribution of each enabled light source.
Each light source contributes the sum of three terms: ambient,
diffuse, and specular. The ambient light source contribution is
the product of the material ambient reflectance and the light's
ambient intensity. The diffuse light source contribution is the
product of the material diffuse reflectance, the light's
diffuse intensity, and the dot product of the vertex's normal
with the normalized vector from the vertex to the light source.
The specular light source contribution is the product of the
material specular reflectance, the light's specular intensity,
and the dot product of the normalized vertex-to-eye and
vertex-to-light vectors, raised to the power of the shininess
of the material. All three light source contributions are
attenuated equally based on the distance from the vertex to the
light source and on light source direction, spread exponent,
and spread cutoff angle. All dot products are replaced with 0
if they evaluate to a negative value.
The alpha component of the resulting lighted color is set
to the alpha value of the material diffuse reflectance.
Errors
GL_INVALID_ENUM is generated if
pname is not an accepted value.
See Also
glLight,
glMaterial
Copyright
Copyright 2003-2004
Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.