GLCONVOLUTIONFILTER1(3G)

NAME
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/.