GLLIGHTMODEL() MachTen Programmer’s Manual GLLIGHTMODEL()

NAME
glLightModelf, glLightModeli, glLightModelfv, glLightMode-
liv - set the lighting model parameters

C SPECIFICATION
void glLightModelf( GLenum pname,
GLfloat param )
void glLightModeli( GLenum pname,
GLint param )

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PARAMETERS
pname Specifies a single-valued lighting model parame-
ter. 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 floating-point
values that specify the ambient RGBA intensity
of the entire scene. Integer values are mapped
linearly such that the most positive repre-
sentable value maps to 1.0, and the most nega-
tive representable value maps to -1.0. Float-
ing-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_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 direc-
tion 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 light-
ing 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 evalu-
ated. Vertices of front-facing polygons are
always lighted using the front material parame-
ters, with no change to their normals. The ini-
tial value is 0.

In RGBA mode, the lighted color of a vertex is the sum of
the material emission intensity, the product of the mate-
rial 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 equa-
tions as in the RGBA case, determine how much above ambi-
ent 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 exe-
cuted between the execution of glBegin and the correspond-
ing 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