glLightModel(3G) OpenGL Reference glLightModel(3G)
NAME
glLightModelf, glLightModeli, glLightModelfv, glLightModeliv - set the
lighting model parameters
C SPECIFICATION
void glLightModelf( GLenum pname,
GLfloat param )
void glLightModeli( GLenum pname,
GLint param )
PARAMETERS
pname Specifies a single-valued lighting model parameter.
GLLIGHTMODELLOCALVIEWER and GLLIGHTMODELTWOSIDE are
accepted.
param Specifies the value that param will be set to.
C SPECIFICATION
void glLightModelfv( GLenum pname,
const GLfloat *params )
void glLightModeliv( GLenum pname,
const GLint *params )
PARAMETERS
pname
Specifies a lighting model parameter. GLLIGHTMODELAMBIENT,
GLLIGHTMODELLOCALVIEWER, and GLLIGHTMODELTWOSIDE 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 three lighting model
parameters:
GLLIGHTMODELAMBIENT
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 positive
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).
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glLightModel(3G) OpenGL Reference glLightModel(3G)
GLLIGHTMODELLOCALVIEWER
params is a single integer or floating-point value that
specifies 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
coordinates. Otherwise, specular reflections are computed from
the origin of the eye coordinate system. The initial value is
0.
GLLIGHTMODELTWOSIDE
params is a single integer 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, 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.
Otherwise, two-sided lighting is specified. In this case,
vertices 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
parameters, 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 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.
In color index mode, the value of the lighted index of a vertex ranges
from the ambient to the specular values passed to glMaterial 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
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glLightModel(3G) OpenGL Reference glLightModel(3G)
RGBA case, determine how much above ambient the resulting index is.
ERRORS
GLINVALIDENUM is generated if pname is not an accepted value.
GLINVALIDOPERATION is generated if glLightModel is executed between the
execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGet with argument GLLIGHTMODELAMBIENT
glGet with argument GLLIGHTMODELLOCALVIEWER
glGet with argument GLLIGHTMODELTWOSIDE
glIsEnabled with argument GLLIGHTING
SEE ALSO
glLight, glMaterial
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