1991-2006 Silicon Graphics, Inc.
glGetConvolutionFilter 3G
glGetConvolutionFilter get current 1D or 2D convolution filter kernel

## C Specification

void `glGetConvolutionFilter` GLenum target GLenum format GLenum type GLvoid * image

## Parameters

target

  The filter to be retrieved. Must be one of `GL_CONVOLUTION_1D` or `GL_CONVOLUTION_2D`.

format

  Format of the output image. 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

  Data type of components in the output image. 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.

image

  Pointer to storage for the output image.

## Description

`glGetConvolutionFilter` returns the current 1D or 2D convolution filter kernel as an image. The one- or two-dimensional image is placed in image according to the specifications in format and type. No pixel transfer operations are performed on this image, but the relevant pixel storage modes are applied.

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

Color components that are present in format but not included in the internal format of the filter are returned as zero. The assignments of internal color components to the components of format are as follows.

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

## Notes

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

The current separable 2D filter must be retrieved with glGetSeparableFilter rather than `glGetConvolutionFilter`.

## Errors

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

`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 image 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 `glGetConvolutionFilter` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGetConvolutionParameter

glGet with argument `GL_PIXEL_PACK_BUFFER_BINDING`

## See Also

glGetSeparableFilter, glConvolutionParameter, glConvolutionFilter1D, glConvolutionFilter2D

## 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/.