1991-2006
Silicon Graphics, Inc.
glGetHistogram
3G

# glGetHistogram

get histogram table

## C Specification

                    void glGetHistogram
                    GLenum target
                    GLboolean reset
                    GLenum format
                    GLenum type
                    GLvoid * values

## Parameters

`target`

  Must be `GL_HISTOGRAM`.

`reset`

  If `GL_TRUE`, each component counter that is actually returned is reset to zero. (Other counters are unaffected.) If `GL_FALSE`, none of the counters in the histogram table is modified.

`format`

  The format of values to be returned in `values`. Must be one of `GL_RED`, `GL_GREEN`, `GL_BLUE`, `GL_ALPHA`, `GL_RGB`, `GL_BGR`, `GL_RGBA`, `GL_BGRA`, `GL_LUMINANCE`, or `GL_LUMINANCE_ALPHA`.

`type`

  The type of values to be returned in `values`. Symbolic constants `GL_UNSIGNED_BYTE`, `GL_BYTE`, `GL_BITMAP`, `GL_UNSIGNED_SHORT`, `GL_SHORT`, `GL_UNSIGNED_INT`, `GL_INT`, `GL_FLOAT`, `GL_UNSIGNED_BYTE_3_3_2`, `GL_UNSIGNED_BYTE_2_3_3_REV`, `GL_UNSIGNED_SHORT_5_6_5`, `GL_UNSIGNED_SHORT_5_6_5_REV`, `GL_UNSIGNED_SHORT_4_4_4_4`, `GL_UNSIGNED_SHORT_4_4_4_4_REV`, `GL_UNSIGNED_SHORT_5_5_5_1`, `GL_UNSIGNED_SHORT_1_5_5_5_REV`, `GL_UNSIGNED_INT_8_8_8_8`, `GL_UNSIGNED_INT_8_8_8_8_REV`, `GL_UNSIGNED_INT_10_10_10_2`, and `GL_UNSIGNED_INT_2_10_10_10_REV` are accepted.

`values`

  A pointer to storage for the returned histogram table.

## Description

`glGetHistogram` returns the current histogram table as a one-dimensional image with the same width as the histogram. No pixel transfer operations are performed on this image, but pixel storage modes that are applicable to 1D images are honored.

If a non-zero named buffer object is bound to the `GL_PIXEL_PACK_BUFFER` target (see glBindBuffer) while a histogram table is requested, `values` is treated as a byte offset into the buffer object's data store.

Color components that are requested in the specified `format`, but which are not included in the internal format of the histogram, are returned as zero. The assignments of internal color components to the components requested by `format` are:

Internal Component | Resulting Component
--- | ---
Red | Red
Green | Green
Blue | Blue
Alpha | Alpha
Luminance | Red

## Notes

`glGetHistogram` is present only if `ARB_imaging` is returned when glGetString is called with an argument of `GL_EXTENSIONS`.

## Errors

`GL_INVALID_ENUM` is generated if `target` is not `GL_HISTOGRAM`.

`GL_INVALID_ENUM` is generated if `format` is not one of the allowable values.

`GL_INVALID_ENUM` is generated if `type` is not one of the allowable values.

`GL_INVALID_OPERATION` is generated if `type` is one of `GL_UNSIGNED_BYTE_3_3_2`, `GL_UNSIGNED_BYTE_2_3_3_REV`, `GL_UNSIGNED_SHORT_5_6_5`, or `GL_UNSIGNED_SHORT_5_6_5_REV` and `format` is not `GL_RGB`.

`GL_INVALID_OPERATION` is generated if `type` is one of `GL_UNSIGNED_SHORT_4_4_4_4`, `GL_UNSIGNED_SHORT_4_4_4_4_REV`, `GL_UNSIGNED_SHORT_5_5_5_1`, `GL_UNSIGNED_SHORT_1_5_5_5_REV`, `GL_UNSIGNED_INT_8_8_8_8`, `GL_UNSIGNED_INT_8_8_8_8_REV`, `GL_UNSIGNED_INT_10_10_10_2`, or `GL_UNSIGNED_INT_2_10_10_10_REV` and `format` is neither `GL_RGBA` nor `GL_BGRA`.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_PACK_BUFFER` target and the buffer object's data store is currently mapped.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_PACK_BUFFER` target and the data would be packed to the buffer object such that the memory writes required would exceed the data store size.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_PACK_BUFFER` target and `values` is not evenly divisible into the number of bytes needed to store in memory a datum indicated by `type`.

`GL_INVALID_OPERATION` is generated if `glGetHistogram` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGetHistogramParameter

glGet with argument `GL_PIXEL_PACK_BUFFER_BINDING`

## See Also

glHistogram, glResetHistogram,

## 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/.