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<STRONG>NAME</STRONG>
<STRONG>glLightModelf,</STRONG> <STRONG>glLightModeli,</STRONG> <STRONG>glLightModelfv,</STRONG> <STRONG>glLightModeliv</STRONG>
- set the lighting model parameters
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glLightModelf</STRONG>( GLenum <EM>pname</EM>,
GLfloat <EM>param</EM> )
void <STRONG>glLightModeli</STRONG>( GLenum <EM>pname</EM>,
GLint <EM>param</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>pname</EM> Specifies a single-valued lighting model parameter.
<STRONG>GL_LIGHT_MODEL_LOCAL_VIEWER</STRONG> and
<STRONG>GL_LIGHT_MODEL_TWO_SIDE</STRONG> are accepted.
<EM>param</EM> Specifies the value that <EM>param</EM> will be set to.
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glLightModelfv</STRONG>( GLenum <EM>pname</EM>,
const GLfloat *<EM>params</EM> )
void <STRONG>glLightModeliv</STRONG>( GLenum <EM>pname</EM>,
const GLint *<EM>params</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>pname</EM>
Specifies a lighting model parameter.
<STRONG>GL_LIGHT_MODEL_AMBIENT</STRONG>, <STRONG>GL_LIGHT_MODEL_LOCAL_VIEWER</STRONG>,
and <STRONG>GL_LIGHT_MODEL_TWO_SIDE</STRONG> are accepted.
<EM>params</EM>
Specifies a pointer to the value or values that <EM>params</EM>
will be set to.
<STRONG>DESCRIPTION</STRONG>
<STRONG>glLightModel</STRONG> sets the lighting model parameter. <EM>pname</EM> names
a parameter and <EM>params</EM> gives the new value. There are three
lighting model parameters:
<STRONG>GL_LIGHT_MODEL_AMBIENT</STRONG>
<EM>params</EM> 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).
<STRONG>GL_LIGHT_MODEL_LOCAL_VIEWER</STRONG>
<EM>params</EM> is a single integer or floating-point value
that specifies how specular reflection angles are
computed. If <EM>params</EM> is 0 (or 0.0), specular
reflection angles take the view direction to be
parallel to and in the direction of the -<EM>z</EM> 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.
<STRONG>GL_LIGHT_MODEL_TWO_SIDE</STRONG>
<EM>params</EM> 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 <EM>params</EM> is 0 (or 0.0), one-
sided lighting is specified, and only the <EM>front</EM>
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 <EM>back</EM> material
parameters, and have their normals reversed before
the lighting equation is evaluated. Vertices of
front-facing polygons are always lighted using the
<EM>front</EM> 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 <STRONG>glMaterial</STRONG> using <STRONG>GL_COLOR_INDEXES</STRONG>. 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.
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>pname</EM> is not an accepted
value.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glLightModel</STRONG> is
executed between the execution of <STRONG>glBegin</STRONG> and the
corresponding execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_LIGHT_MODEL_AMBIENT</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_LIGHT_MODEL_LOCAL_VIEWER</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_LIGHT_MODEL_TWO_SIDE</STRONG>
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_LIGHTING</STRONG>
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glLight</STRONG>, <STRONG>glMaterial</STRONG>
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