glLightMode
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 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_LOCAL_VIEWER
and GL_LIGHT_MODEL_TWO_SIDE are accepted.
- params
-
Specifies a pointer to the value 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 default 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 default 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 default 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 sourcecontribution 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 zero 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.
ERRORS
GL_INVALID_ENUM is generated if pname is not an accepted value.
GL_INVALID_OPERATION is generated if glLightModel is called
between a call to glBegin and the
corresponding call to 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,
glMaterial
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© 1995 Uwe Behrens. All rights reserved.