1991-2006 Silicon Graphics, Inc.
glLightModel 3G
glLightModel 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 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).

`GL_LIGHT_MODEL_COLOR_CONTROL`

  params must be either `GL_SEPARATE_SPECULAR_COLOR` or `GL_SINGLE_COLOR`. `GL_SINGLE_COLOR` specifies 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 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.

## 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, glMaterial

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.