GLLIGHTMODEL(3G) 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 inten-sity intensity
sity 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 spec-ifies specifies
ifies 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 twosided
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 prod-uct product
uct 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 specu-lar specular
lar 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)
GLLIGHTMODEL(3G)
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