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glLightf, glLighti, glLightfv, glLightiv

These functions set light-source parameters.

void glLightf(
  GLenum light,
  GLenum pname,
  GLfloat param
);

void glLighti(
  GLenum light,
  GLenum pname,
  GLint param
);

Parameters

light
The identifier of a light. The number of lights available depends on the implementation, but at least eight lights are supported. They are identified by symbolic names of the form GL_LIGHTi where i is a value: 0 to GL_MAX_LIGHTS - 1.
pname
A single-valued light-source parameter for light. The following values are accepted.
Value Meaning
GL_SPOT_EXPONENT The params parameter is a single integer or floating-point value that specifies the intensity distribution of the light. Integer and floating-point values are mapped directly. Only values in the range [0,128] are accepted.
GL_SPOT_CUTOFF Effective light intensity is attenuated by the cosine of the angle between the direction of the light and the direction from the light to the vertex being lighted, raised to the power of the spot exponent. Thus, higher spot exponents result in a more focused light source, regardless of the spot cutoff angle (see the following paragraph). The default spot exponent is 0, resulting in uniform light distribution.
GL_CONSTANT_ATTENUATION
GL_LINEAR_ATTENUATION
GL_QUADRATIC_ATTENUATION
The params parameter is a single integer or floating-point value that specifies the maximum spread angle of a light source. Integer and floating-point values are mapped directly. Only values in the range [0,90], and the special value 180, are accepted. If the angle between the direction of the light and the direction from the light to the vertex being lighted is greater than the spot cutoff angle, then the light is completely masked. Otherwise, its intensity is controlled by the spot exponent and the attenuation factors. The default spot cutoff is 180, resulting in uniform light distribution.

The params parameter is a single integer or floating-point value that specifies one of the three light attenuation factors. Integer and floating-point values are mapped directly. Only nonnegative values are accepted. If the light is positional, rather than directional, its intensity is attenuated by the reciprocal of the sum of: the constant factor, the linear factor multiplied by the distance between the light and the vertex being lighted, and the quadratic factor multiplied by the square of the same distance. The default attenuation factors are (1,0,0), resulting in no attenuation.


param
The value to which parameter pname of light source light will be set.
void glLightfv(
  GLenum light,
  GLenum pname,
  const GLfloat *params
);

void glLightiv(
  GLenum light,
  GLenum pname,
  const GLint *params
);

Parameters

light
A light. The number of lights depends on the implementation, but at least eight lights are supported. They are identified by symbolic names of the form GL_LIGHTi where 0 &le; i < GL_MAX_LIGHTS.
pname
A light source parameter for light. The following values are accepted:
Value Meaning
GL_AMBIENT The params parameter contains four integer or floating-point values that specify the ambient RGBA intensity of the light. 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 light intensity is (0.0, 0.0, 0.0, 1.0).
GL_DIFFUSE The params parameter contains four integer or floating-point values that specify the diffuse RGBA intensity of the light. 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 diffuse intensity is (0.0, 0.0, 0.0, 1.0) for all lights other than light zero. The default diffuse intensity of light zero is (1.0, 1.0, 1.0, 1.0).
GL_SPECULAR The params parameter contains four integer or floating-point values that specify the specular RGBA intensity of the light. 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 specular intensity is (0.0, 0.0, 0.0, 1.0) for all lights other than light zero. The default specular intensity of light zero is (1.0, 1.0, 1.0, 1.0).
GL_POSITION The params parameter contains four integer or floating-point values that specify the position of the light in homogeneous object coordinates. Both integer and floating-point values are mapped directly. Neither integer nor floating-point values are clamped.

The position is transformed by the modelview matrix when glLight is called (just as if it were a point), and it is stored in eye coordinates. If the w component of the position is 0.0, the light is treated as a directional source. Diffuse and specular lighting calculations take the lights direction, but not its actual position, into account, and attenuation is disabled. Otherwise, diffuse and specular lighting calculations are based on the actual location of the light in eye coordinates, and attenuation is enabled. The default position is (0,0,1,0); thus, the default light source is directional, parallel to, and in the direction of the z axis.

GL_SPOT_DIRECTION The params parameter contains three integer or floating-point values that specify the direction of the light in homogeneous object coordinates. Both integer and floating-point values are mapped directly. Neither integer nor floating-point values are clamped.

The spot direction is transformed by the inverse of the modelview matrix when glLight is called (just as if it were a normal), and it is stored in eye coordinates. It is significant only when GL_SPOT_CUTOFF is not 180, which it is by default. The default direction is (0,0,1).

GL_SPOT_EXPONENT The params parameter is a single integer or floating-point value that specifies the intensity distribution of the light. Integer and floating-point values are mapped directly. Only values in the range [0,128] are accepted.

Effective light intensity is attenuated by the cosine of the angle between the direction of the light and the direction from the light to the vertex being lighted, raised to the power of the spot exponent. Thus, higher spot exponents result in a more focused light source, regardless of the spot cutoff angle (see the following paragraph). The default spot exponent is 0, resulting in uniform light distribution.

GL_SPOT_CUTOFF The params parameter is a single integer or floating-point value that specifies the maximum spread angle of a light source. Integer and floating-point values are mapped directly. Only values in the range [0,90], and the special value 180, are accepted. If the angle between the direction of the light and the direction from the light to the vertex being lighted is greater than the spot cutoff angle, then the light is completely masked. Otherwise, its intensity is controlled by the spot exponent and the attenuation factors. The default spot cutoff is 180, resulting in uniform light distribution.
GL_CONSTANT_ATTENUATION
GL_LINEAR_ATTENUATION
GL_QUADRATIC_ATTENUATION
The params parameter is a single integer or floating-point value that specifies one of the three light attenuation factors. Integer and floating-point values are mapped directly. Only nonnegative values are accepted. If the light is positional, rather than directional, its intensity is attenuated by the reciprocal of the sum of: the constant factor, the linear factor multiplied by the distance between the light and the vertex being lighted, and the quadratic factor multiplied by the square of the same distance. The default attenuation factors are (1,0,0), resulting in no attenuation.

params
A pointer to the value or values to which parameter pname of light source light will be set.

Remarks

The glLight function sets the values of individual light source parameters. The light parameter names the light and is a symbolic name of the form:

GL_LIGHTi, where 0 &le; i < GL_MAX_LIGHTS

The pname parameter specifies one of the light source parameters, again by symbolic name. The params parameter is either a single value or a pointer to an array that contains the new values.

Lighting calculation is enabled and disabled using glEnable and glDisable with argument GL_LIGHTING. When lighting is enabled, light sources that are enabled contribute to the lighting calculation. Light source i is enabled and disabled using glEnable and glDisable with argument GL_LIGHTi.

It is always the case that GL_LIGHTi = GL_LIGHT0 + i.

The following functions retrieve information related to the glLight function:

glGetLight

glIsEnabled with argument GL_LIGHTING

Error Codes

The following are the error codes generated and their conditions.

Error code Condition
GL_INVALID_ENUM light or pname was not an accepted value.
GL_INVALID_VALUE a spot exponent value was specified outside the range [0,128], or if spot cutoff was specified outside the range [0,90] (except for the special value 180), or if a negative attenuation factor was specified.
GL_INVALID_OPERATION glLight was called between a call to glBegin and the corresponding call to glEnd.

Requirements

  Windows NT/2000: Requires Windows NT 3.5 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in Gl.h.
  Library: Use Opengl32.lib.

See Also

glBegin, glColorMaterial, glEnd, glLightModel, glMaterial


  

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