glLightModel Subroutine

OpenGL 1.1 for AIX: Reference Manual

glLightModel Subroutine

Purpose

Sets the lighting model parameters.

Library

OpenGL C bindings library: libGL.a

C Syntax

void glLightModelf(GLenum ParameterName,
      GLfloat Parameter)

void glLightModeli(GLenum ParameterName,
      GLint Parameter)

void glLightModelfv(GLenum ParameterName,
      const GLfloat *ParameterValues)

void glLightModeliv(GLenum ParameterName,
      const GLint *ParameterValues)

Parameters

ParameterName	For glLightModelf and glLightModeli, this parameter specifies a single-valued lighting model parameter. GL_LIGHT_MODEL_LOCAL_VIEWER and GL_LIGHT_MODEL_TWO_SIDE are accepted. For glLightModelfv and glLightModeliv, this parameter specifies a lighting model parameter. GL_LIGHT_MODEL_AMBIENT, GL_LIGHT_MODEL_LOCAL_VIEWER, and GL_LIGHT_MODEL_TWO_SIDE are accepted.
Parameter	Specifies the value to which ParameterName is set. This parameter applies only to glLightModelf and glLightModeli.
ParameterValues	Specifies a pointer to the value or values to which ParameterName is set. This parameter applies only to glLightModelfv and glLightModeliv.

Description

The glLightModel subroutine sets the lighting model parameters. ParameterName names a parameter and ParameterValues gives the new value. There are three lighting model parameters:

GL_LIGHT_MODEL_AMBIENT	ParameterValues contains four integer or floating-point values that specify the ambient red, green, blue, alpha (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 default ambient scene intensity is (0.2, 0.2, 0.2, 1.0).
GL_LIGHT_MODEL_LOCAL_VIEWER	ParameterValues is a single integer or floating-point value that specifies how specular reflection angles are computed. If ParameterValues is 0 (or 0.0), specular reflections are computed from the origin of the eye coordinate system. Otherwise, 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. The default is False.
GL_LIGHT_MODEL_TWO_SIDE	ParameterValues is a single integer or floating-point value that specifies whether one-sided or two-sided lighting calculations are done for polygons. It has no effect on the lighting calculations for points, lines, or bitmaps. If ParameterValues 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 backfacing polygons are lighted using the back material parameters, and have their normals reversed before the lighting equation is evaluated. Vertices of frontfacing polygons are always lighted using the front material parameters, with no change to their normals. The default is False.

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 (zero) if they are 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. The extent to which the resulting index is above ambient is determined by diffuse and specular coefficients, computed with a weighting of the lights' colors (.30, .59, .11); the shininess of the material; and the same reflection and attenuation equations as in the RGBA case.

Errors

GL_INVALID_ENUM	ParameterName is not an accepted value.
GL_INVALID_OPERATION	The glLightModel subroutine is called between a call to glBegin and the corresponding call to glEnd.

Associated Gets

Associated gets for the glLightModel subroutine are as follows. (See the glGet subroutine for more information.)

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.

Files

/usr/include/GL/gl.h

Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL.

Related Information

The glBegin or glEnd subroutine, glEnable or glDisable subroutine, glLight subroutine, glMaterial subroutine.

OpenGL Overview.