2003-2004 Silicon Graphics, Inc.
glLightModel 3G
glLightModel glLightModelf glLightModelx glLightModelfv glLightModelxv set the lighting model parameters

## C Specification

void `glLightModelf` GLenum pname GLfloat param void `glLightModelx` GLenum pname GLfixed param

## Parameters

pname

  Specifies a single-valued lighting model parameter. Must be `GL_LIGHT_MODEL_TWO_SIDE`.

param

  Specifies the value that param will be set to.

## C Specification

void `glLightModelfv` GLenum pname const GLfloat * params void `glLightModelxv` GLenum pname const GLfixed * params

## Parameters

pname

  Specifies a lighting model parameter. `GL_LIGHT_MODEL_AMBIENT` 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 two lighting model parameters:

`GL_LIGHT_MODEL_AMBIENT`

  params contains four fixed-point or floating-point values that specify the ambient intensity of the entire scene. The values are not clamped. The initial value is (0.2, 0.2, 0.2, 1.0).

`GL_LIGHT_MODEL_TWO_SIDE`

  params is a single fixed-point 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 or lines. If params is 0, one-sided lighting is specified, and both front- and back-facing polygons are assigned the same computed color. Otherwise, two-sided lighting is specified. In this case, vertices of back-facing polygons have their normals reversed before the lighting equation is evaluated. Vertices of front-facing polygons are always lighted with no change to their normals. The initial value is 0. Note that there is only one set of material properties shared by both front- and back-facing polygons.

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.

## Errors

`GL_INVALID_ENUM` is generated if pname is not an accepted value.

## See Also

glLight, glMaterial

## Copyright

Copyright 2003-2004 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.