fglFragmentLightModel(3G) OpenGL Reference fglFragmentLightModel(3G)NAME
fglFragmentLightModelfSGIX, fglFragmentLightModeliSGIX,
fglFragmentLightModelfvSGIX, fglFragmentLightModelivSGIX - set the
lighting model parameters
FORTRAN SPECIFICATION
SUBROUTINE fglFragmentLightModelfSGIX( INTEGER*4 pname,
REAL*4 param )
SUBROUTINE fglFragmentLightModeliSGIX( INTEGER*4 pname,
INTEGER*4 param )
PARAMETERS
pname Specifies a single-valued lighting model parameter.
GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX,
GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX, and
GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX are accepted.
param Specifies the value that param will be set to.
FORTRAN SPECIFICATION
SUBROUTINE fglFragmentLightModelfvSGIX( INTEGER*4 pname,
CHARACTER*8 params )
SUBROUTINE fglFragmentLightModelivSGIX( INTEGER*4 pname,
CHARACTER*8 params )
PARAMETERS
pname
Specifies a lighting model parameter.
GL_FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX,
GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX,
GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX, and
GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX are accepted.
params
Specifies a pointer to the value or values that params will be set
to.
DESCRIPTION
fglFragmentLightModel sets the lighting model parameter. pname names a
parameter and params gives the new value. There are three lighting model
parameters:
GL_FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX
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
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fglFragmentLightModel(3G) OpenGL Reference fglFragmentLightModel(3G)
clamped. The initial ambient scene intensity is (0.2, 0.2,
0.2, 1.0).
GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX
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 fragment in eye
coordinates. Otherwise, specular reflections are computed from
the origin of the eye coordinate system. The initial value is
0.
GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX
params must be either GL_FLAT or GL_SMOOTH, and controls how
normals are selected for use in the fragment lighting
computations. If GL_FLAT is selected for the lighting model,
the normal from the provoking vertex of the primitive is used
for all fragment lighting computations. If GL_SMOOTH is
specified a normal is computed for each fragment using the
normals from all of the vertices of the primitive.
GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX
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 initial value
is 0.
In RGBA mode, the lighted color of a fragment 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 fragment's normal with the
normalized vector from the fragment 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 fragment-to-eye and fragment-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
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fglFragmentLightModel(3G) OpenGL Reference fglFragmentLightModel(3G)
fragment 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 fragment ranges
from the ambient to the specular values passed to fglFragmentMaterial
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 fglFragmentLightModel is executed
between the execution of fglBegin and the corresponding execution of
fglEnd.
ASSOCIATED GETS
fglGet with argument GL_FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX
fglGet with argument GL_FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX
fglGet with argument GL_FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX
fglGet with argument GL_FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX
fglIsEnabled with argument GL_FRAGMENT_LIGHTING_SGIX
MACHINE DEPENDENCIES
The SGIX_fragment_lighting extension is supported only on Octane2 VPro
systems.
On Octane2 VPro systems, use of the texture q coordinate to achieve
projective texture effects will be processed on a per-vertex basis
instead of a per-pixel basis, unless the texture matrix is set up to be
projective. (A projective texture matrix, specified as 16-element array
M, is defined to be one in which any of the M[3], M[7], or M[11] array
elements is non-zero.) In addition, if either two-sided lighting or
fragment lighting or separate specular lighting is in effect, projective
texture effects will always be processed on a per-vertex basis.
SEE ALSO
fglFragmentLight, fglFragmentMaterial
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