HP c3700 - Workstation, Reference Manual, Page: 255 / 486

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glLightModel
Chapter 10
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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 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 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 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