

 
Manual Reference Pages  GLLIGHTMODELI (3)
NAME
glLightModelf, glLightModeli, glLightModelfv, glLightModeliv  set the lighting model parameters
CONTENTS
C Specification
Parameters
C Specification
Parameters
Description
Errors
Associated Gets
See Also
C SPECIFICATION
void glLightModelf(
GLenum pname,
GLfloat param )
void glLightModeli(
GLenum pname,
GLint param )
PARAMETERS
pname

Specifies a singlevalued 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 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 floatingpoint 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.
Floatingpoint values are mapped directly.
Neither integer nor floatingpoint values are clamped.
The initial ambient scene intensity is (0.2, 0.2, 0.2, 1.0).

GL_LIGHT_MODEL_LOCAL_VIEWER
 
params is a single integer or floatingpoint 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 floatingpoint value that specifies
whether one or twosided 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), onesided lighting is specified,
and only the front material parameters are used in the
lighting equation.
Otherwise, twosided lighting is specified.
In this case, vertices of backfacing polygons are lighted using the
back material parameters,
and have their normals reversed before the lighting equation is evaluated.
Vertices of frontfacing 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 fullscene
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 vertextoeye and vertextolight
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.
ERRORS
GL_INVALID_ENUM is generated if pname is not an accepted value.
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_LOCAL_VIEWER
glGet with argument GL_LIGHT_MODEL_TWO_SIDE
glIsEnabled with argument GL_LIGHTING
SEE ALSO
glLight,
glMaterial
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