GLLIGHTMODEL(3G) UNIX Programmer's Manual 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 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
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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 com-
putation 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 equa-
tion. 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 nor-
mals. 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
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dot product of the vertex's normal with the normalized vec-
tor 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 exe-
cuted 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)
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