GLLIGHTMODEL(3G) 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. GL_LIGHT_MODEL_LOCAL_VIEWER, GL_LIGHT_MODEL_COLOR_CONTROL, and
GL_LIGHT_MODEL_TWO_SIDE 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_COLOR_CONTROL, GL_LIGHT_MODEL_LOCAL_VIEWER, 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 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 val-
ues 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_COLOR_CONTROL
params must be either GL_SEPARATE_SPECULAR_COLOR or GL_SINGLE_COLOR. GL_SINGLE_COLOR specifies that a single color is generated
from the lighting computation for a vertex. GL_SEPARATE_SPECULAR_COLOR 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 application of texture mapping (if enabled). The initial value is GL_SINGLE_COLOR.
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 coordi-
nate 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 nor-
mals 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
GL_COLOR_INDEXES. 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
GL_LIGHT_MODEL_COLOR_CONTROL is available only if the GL version is 1.2 or greater.
ERRORS
GL_INVALID_ENUM is generated if pname is not an accepted value.
GL_INVALID_ENUM is generated if pname is GL_LIGHT_MODEL_COLOR_CONTROL and params is not one of GL_SINGLE_COLOR or
GL_SEPARATE_SPECULAR_COLOR.
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_COLOR_CONTROL
glGet with argument GL_LIGHT_MODEL_LOCAL_VIEWER
glGet with argument GL_LIGHT_MODEL_TWO_SIDE
glIsEnabled with argument GL_LIGHTING
SEE ALSO
glLight(3G), glMaterial(3G)
GLLIGHTMODEL(3G)