glLightf function
The glLightf function returns light source parameter values.
Syntax
void WINAPI glLightf(
GLenum light,
GLenum pname,
GLfloat param
);
Parameters
-
light
-
The identifier of a light. The number of possible lights 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 symbolic names are accepted.
Value Meaning - GL_SPOT_EXPONENT
The param parameter is a single floating-point value that specifies the intensity distribution of the light. 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. The default spot exponent is 0, resulting in uniform light distribution.- GL_SPOT_CUTOFF
The param parameter is a single floating-point value that specifies the maximum spread angle of a light source. 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 param parameter is a single floating-point value that specifies one of the three light attenuation factors. 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
-
Specifies the value that parameter pname of light source light will be set to.
Return value
This function does not return a value.
Error codes
The following error codes can be retrieved by the glGetError function.
| Name | Meaning |
|---|---|
|
light or pname was not an accepted value. |
|
A spot exponent value was specified outside the range [0, 128], or spot cutoff was specified outside the range [0, 90] (except for the special value 180), or a negative attenuation factor was specified. |
|
The function was called between a call to glBegin and the corresponding call to glEnd. |
Remarks
The glLightf function sets the value or values of individual light source parameters. The light parameter names the light and is a symbolic name of the form GL_LIGHTi, where 0 = i < GL_MAX_LIGHTS.
The pname parameter specifies one of the light source parameters, again by symbolic name. The param 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 glLightf function:
glIsEnabled with argument GL_LIGHTING
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client |
Windows 2000 Professional [desktop apps only] |
| Minimum supported server |
Windows 2000 Server [desktop apps only] |
| Header |
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| Library |
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| DLL |
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