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 )
delim $$
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 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_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 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.
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 ALSOglLight(3G), glMaterial(3G)
March 1, 2011
