glLightModel
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.
GL_LIGHT_MODEL_LOCAL_VIEWER, GL_LIGHT_MODEL_TWO_SIDE,
and GL_LIGHT_MODEL_COLOR_CONTROL_EXT 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. GL_LIGHT_MODEL_AMBIENT,
GL_LIGHT_MODEL_LOCAL_VIEWER, GL_LIGHT_MODEL_TWO_SIDE,
and GL_LIGHT_MODEL_COLOR_CONTROL_EXT 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:
- GL_LIGHT_MODEL_AMBIENT
-
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).
- GL_LIGHT_MODEL_LOCAL_VIEWER
-
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.
- GL_LIGHT_MODEL_TWO_SIDE
-
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.
- GL_LIGHT_MODEL_COLOR_CONTROL_EXT
-
params is a single integer or floating-point value and must be either
GL_SINGLE_COLOR_EXT or GL_SEPARATE_SPECULAR_COLOR_EXT. If
params is GL_SEPARATE_SPECULAR_COLOR_EXT the specular
contribution to lighting is computed as a separate value and added to the
color after the application of the texture mapping (if enabled).
The fragment color is the color produced by lighting without the specular
contribution. If params is GL_SINGLE_COLOR_EXT, lighting
produces a single color used as the fragment color which includes the
specular contribution and no additional color is added to the color
produced by the texture function. If lighting is disabled, the current
color is used as the fragment color and no additional color is added to the
color produced by the texture function. The initial value is
GL_SINGLE_COLOR_EXT.
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 GL_COLOR_INDEXES. Diffuse
and specular coefficients, computed with a (0.30,0.59,0.11)
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.
EXTENSIONS
Some routines and constants for this function are part of an extension, not part of the
core GL command set. The following extension names must be present in the string returned by
glGetString when called with argument GL_EXTENSIONS
to use these routines and constants.
- GL_EXT_separate_specular_color
-
GL_LIGHT_MODEL_COLOR_CONTROL_EXT, GL_SINGLE_COLOR_EXT, and
GL_SEPARATE_SPECULAR_COLOR_EXT
are part of the EXT_separate_specular_color extension.
ERRORS
GL_INVALID_ENUM is generated if pname is not an accepted value.
GL_INVALID_OPERATION is generated if glLightModel is executed
between the execution of glBegin and the
corresponding execution of glEnd.
ASSOCIATED GETS
glGet with argument GL_LIGHT_MODEL_AMBIENT
glGet with argument GL_LIGHT_MODEL_LOCAL_VIEWER
glGet with argument GL_LIGHT_MODEL_TWO_SIDE
glIsEnabled with argument GL_LIGHTING
SEE ALSO
glLight,