1991-2006 Silicon Graphics, Inc.
glConvolutionFilter1D 3G
glConvolutionFilter1D define a one-dimensional convolution filter

## C Specification

void `glConvolutionFilter1D` GLenum target GLenum internalformat GLsizei width GLenum format GLenum type const GLvoid * data

## Parameters

target

  Must be `GL_CONVOLUTION_1D`.

internalformat

  The internal format of the convolution filter kernel. The allowable values are `GL_ALPHA`, `GL_ALPHA4`, `GL_ALPHA8`, `GL_ALPHA12`, `GL_ALPHA16`, `GL_LUMINANCE`, `GL_LUMINANCE4`, `GL_LUMINANCE8`, `GL_LUMINANCE12`, `GL_LUMINANCE16`, `GL_LUMINANCE_ALPHA`, `GL_LUMINANCE4_ALPHA4`, `GL_LUMINANCE6_ALPHA2`, `GL_LUMINANCE8_ALPHA8`, `GL_LUMINANCE12_ALPHA4`, `GL_LUMINANCE12_ALPHA12`, `GL_LUMINANCE16_ALPHA16`, `GL_INTENSITY`, `GL_INTENSITY4`, `GL_INTENSITY8`, `GL_INTENSITY12`, `GL_INTENSITY16`, `GL_R3_G3_B2`, `GL_RGB`, `GL_RGB4`, `GL_RGB5`, `GL_RGB8`, `GL_RGB10`, `GL_RGB12`, `GL_RGB16`, `GL_RGBA`, `GL_RGBA2`, `GL_RGBA4`, `GL_RGB5_A1`, `GL_RGBA8`, `GL_RGB10_A2`, `GL_RGBA12`, or `GL_RGBA16`.

width

  The width of the pixel array referenced by data.

format

  The format of the pixel data in data. The allowable values are `GL_ALPHA`, `GL_LUMINANCE`, `GL_LUMINANCE_ALPHA`, `GL_INTENSITY`, `GL_RGB`, and `GL_RGBA`.

type

  The type of the pixel data in data. 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.

data

  Pointer to a one-dimensional array of pixel data that is processed to build the convolution filter kernel.

## Description

`glConvolutionFilter1D` builds a one-dimensional convolution filter kernel from an array of pixels.

The pixel array specified by width, format, type, and data is extracted from memory and processed just as if glDrawPixels were called, but processing stops after the final expansion to RGBA is completed.

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

The R, G, B, and A components of each pixel are next scaled by the four 1D `GL_CONVOLUTION_FILTER_SCALE` parameters and biased by the four 1D `GL_CONVOLUTION_FILTER_BIAS` parameters. (The scale and bias parameters are set by glConvolutionParameter using the `GL_CONVOLUTION_1D` target and the names `GL_CONVOLUTION_FILTER_SCALE` and `GL_CONVOLUTION_FILTER_BIAS`. The parameters themselves are vectors of four values that are applied to red, green, blue, and alpha, in that order.) The R, G, B, and A values are not clamped to [0,1] at any time during this process.

Each pixel is then converted to the internal format specified by internalformat. This conversion simply maps the component values of the pixel (R, G, B, and A) to the values included in the internal format (red, green, blue, alpha, luminance, and intensity). The mapping is as follows:

Internal Format | Red | Green | Blue | Alpha | Luminance | Intensity
--- | --- | --- | --- | --- | --- | ---
`GL_ALPHA` |  |  |  | A |  |
`GL_LUMINANCE` |  |  |  |  | R |
`GL_LUMINANCE_ALPHA` |  |  |  | A | R |
`GL_INTENSITY` |  |  |  |  |  | R
`GL_RGB` | R | G | B |  |  |
`GL_RGBA` | R | G | B | A |  |

The red, green, blue, alpha, luminance, and/or intensity components of the resulting pixels are stored in floating-point rather than integer format. They form a one-dimensional filter kernel image indexed with coordinate i such that i starts at 0 and increases from left to right. Kernel location i is derived from the ith pixel, counting from 0.

Note that after a convolution is performed, the resulting color components are also scaled by their corresponding `GL_POST_CONVOLUTION_c_SCALE` parameters and biased by their corresponding `GL_POST_CONVOLUTION_c_BIAS` parameters (where c takes on the values RED, GREEN, BLUE, and ALPHA). These parameters are set by glPixelTransfer.

## Notes

`glConvolutionFilter1D` 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_CONVOLUTION_1D`.

`GL_INVALID_ENUM` is generated if internalformat 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_VALUE` is generated if width is less than zero or greater than the maximum supported value. This value may be queried with glGetConvolutionParameter using target `GL_CONVOLUTION_1D` and name `GL_MAX_CONVOLUTION_WIDTH`.

`GL_INVALID_OPERATION` is generated if format 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 type is not `GL_RGB`.

`GL_INVALID_OPERATION` is generated if format 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 type 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_UNPACK_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_UNPACK_BUFFER` target and the data would be unpacked from the buffer object such that the memory reads 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_UNPACK_BUFFER` target and data 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 `glConvolutionFilter1D` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGetConvolutionParameter, glGetConvolutionFilter

glGet with argument `GL_PIXEL_UNPACK_BUFFER_BINDING`

## See Also

glConvolutionFilter2D, glSeparableFilter2D, glConvolutionParameter, glPixelTransfer

## 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/.