GLIGHTMODEL(3G) GLIGHTMODEL(3G)
NAME
glLightodelf,, glLightodeli,, glLightodelfv,, glLightodeliv - set the
lighting model parameters
C SPECIFICATION
void glLightodelf( GLenum pname,
GLfloat param )
void glLightodeli( GLenum pname,
GLint param )
PARAMETERS
pname Specifies a single-valued lighting model parameter.
GLIGHTMODELOCALVIEWER, GLIGHTMODELCOLORCONTROL, and
GLIGHTMODELTWOSIDE are accepted.
param Specifies the value that param will be set to.
C SPECIFICATION
void glLightodelfv( GLenum pname,
const GLfloat *params )
void glLightodeliv( GLenum pname,
const GLint *params )
PARAMETERS
pname Specifies a lighting model parameter. GLIGHTMODELAMBIENT,
GLIGHTMODELCOLORCONTROL, GLIGHTMODELOCALVIEWER, and
GLIGHTMODELTWOSIDE are accepted.
params Specifies a pointer to the value or values that params will be
set to.
DESCRIPTION
glLightodel sets the lighting model parameter. pname names a parame-
ter and params gives the new value. There are three lighting model
parameters:
GLIGHTMODELAMBIENT
params contains four integer or floating-point values that
specify the ambient RGBA intensity of the entire scene.
Integer values are mapped linearly such that the most posi-
tive representable value maps to 1.0, and the most negative
representable value maps to -1.0. Floating-point values are
mapped directly. Neither integer nor floating-point values
are clamped. The initial ambient scene intensity is (0.2,
0.2, 0.2, 1.0).
GLIGHTMODELCOLORCONTROL
params must be either GLSEPARATESPECULARCOLOR or
GLSINGLECOLOR. GLSINGLECOLOR specifies that a single
color is generated from the lighting computation for a ver-
tex. GLSEPARATESPECULARCOLOR specifies that the specular
color computation of lighting be stored separately from the
remainder of the lighting computation. The specular color is
summed into the generated fragment's color after the applica-
tion of texture mapping (if enabled). The initial value is
GLSINGLECOLOR.
GLIGHTMODELOCALVIEWER
params is a single integer or floating-point value that spec-
ifies how specular reflection angles are computed. If params
is 0 (or 0.0), specular reflection angles take the view
direction to be parallel to and in the direction of the -z
axis, regardless of the location of the vertex in eye coordi-
nates. Otherwise, specular reflections are computed from the
origin of the eye coordinate system. The initial value is 0.
GLIGHTMODELTWOSIDE
params is a single integer or floating-point value that spec-
ifies whether one- or two-sided lighting calculations are
done for polygons. It has no effect on the lighting calcula-
tions for points, lines, or bitmaps. If params is 0 (or
0.0), one-sided lighting is specified, and only the front
material parameters are used in the lighting equation. Oth-
erwise, two-sided lighting is specified. In this case, ver-
tices of back-facing polygons are lighted using the back
material parameters, and have their normals reversed before
the lighting equation is evaluated. Vertices of front-facing
polygons are always lighted using the front material parame-
ters, with no change to their normals. The initial value is
0.
In RGBA mode, 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 normal-
ized 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 contri-
butions 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.
In color index mode, the value of the lighted index of a vertex ranges
from the ambient to the specular values passed to glaterial using
GLCOLORINDEXES. Diffuse and specular coefficients, computed with a
(.30, .59, .11) weighting of the lights' colors, the shininess of the
material, and the same reflection and attenuation equations as in the
RGBA case, determine how much above ambient the resulting index is.
NOTES
GLIGHTMODELCOLORCONTROL is available only if the GL version is 1.2
or greater.
ERORS
GLINVALIDENUM is generated if pname is not an accepted value.
GLINVALIDENUM is generated if pname is GLIGHTMODELCOLORCONTROL
and params is not one of GLSINGLECOLOR or GLSEPARATESPECULARCOLOR.
GLINVALIDOPERATION is generated if glLightodel is executed between
the execution of glBegin and the corresponding execution of glEnd.
ASOCIATED GETS
glGet with argument GLIGHTMODELAMBIENT
glGet with argument GLIGHTMODELCOLORCONTROL
glGet with argument GLIGHTMODELOCALVIEWER
glGet with argument GLIGHTMODELTWOSIDE
glIsEnabled with argument GLIGHTING
SEE ALSO
glLight, glaterial
GLIGHTMODEL(3G)
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