GLLIGHTMODEL
Section: Misc. Reference Manual Pages (3G)
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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 ALSO
glLight(3G),
glMaterial(3G)