glSeparableFilter2DEXT

NAME

glSeparableFilter2DEXT - define a separable two-dimensional convolution filter

C SPECIFICATION

void glSeparableFilter2DEXT(GLenum target,
                            GLenum internalformat,
                            GLsizei width,
                            GLsizei height,
                            GLenum format,
                            GLenum type,
                            const GLvoid *row,
                            const GLvoid *column)

PARAMETERS

target	Must be GL_SEPARABLE_2D_EXT.
internalformat	The internal format of the convolution filter kernel. The allowable values are GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_INTENSITY_EXT, GL_RGB, and GL_RGBA.
width	The number of elements in the pixel array referenced by row. (This is the width of the separable filter kernel.)
height	The number of elements in the pixel array referenced by column. (This is the height of the separable filter kernel.)
format	The format of the pixel data. The allowable values are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB, GL_RGBA, GL_BGR_EXT, GL_BGRA_EXT, GL_422_EXT, GL_422_REV_EXT, GL_422_AVERAGE_EXT, and GL_422_REV_AVERAGE_EXT.
type	Specifies the data type for pixel data. The allowable values are GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2_EXT, GL_UNSIGNED_BYTE_2_3_3_REV_EXT, GL_UNSIGNED_SHORT_5_6_5_EXT, GL_UNSIGNED_SHORT_5_6_5_REV_EXT, GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_4_4_4_4_REV_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT, GL_UNSIGNED_SHORT_1_5_5_5_REV_EXT, GL_UNSIGNED_INT_8_8_8_8_EXT, GL_UNSIGNED_INT_8_8_8_8_REV_EXT, GL_UNSIGNED_INT_10_10_10_2_EXT, and GL_UNSIGNED_INT_2_10_10_10_REV_EXT.
row	Pointer to a one-dimensional array of pixel data that is processed to build the row filter kernel.
column	Pointer to a one-dimensional array of pixel data that is processed to build the column filter kernel.

DESCRIPTION

glSeparableFilter2DEXT builds a two-dimensional separable convolution filter kernel from two arrays of pixels. The pixel arrays specified by (width, format, type, row) and (height, format, type, column) are processed just as if they had been passed to glDrawPixels, but processing stops after the final expansion to RGBA is completed. The formats GL_COLOR_INDEX, GL_DEPTH_COMPONENT, and GL_STENCIL_INDEX and the type GL_BITMAP are not allowed.

The R, G, B, and A components of each pixel are scaled by the four 2D GL_CONVOLUTION_FILTER_SCALE_EXT parameters and biased by the four 2D GL_CONVOLUTION_FILTER_BIAS_EXT parameters. (The scale and bias parameters are set by glConvolutionParameterEXT using the GL_CONVOLUTION_2D_EXT target and the names GL_CONVOLUTION_FILTER_SCALE_EXT and GL_CONVOLUTION_FILTER_BIAS_EXT. 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 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:

internalformat 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 - -

internalformat	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 intensity components of the resulting pixels are stored in floating-point rather than integer format. They form a two-dimensional filter kernel image indexed with coordinate i and j such that i starts at 0 and increases from left to right, and j starts at 0 and increases from bottom to top. Kernel location (i, j) is derived from the n^th pixel, where n is i + j * width.

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

EXTENSIONS

Some routines and constants for this function are part of an extension, not part of the core GL command set. The following extension names must be present in the string returned by glGetString when called with argument GL_EXTENSIONS to use these routines and constants.

GL_EXT_422_pixels: GL_422_EXT, GL_422_REV_EXT, GL_422_AVERAGE_EXT, and GL_422_REV_AVERAGE_EXT are part of the EXT_422_pixels extension.
GL_EXT_bgra: GL_BGR_EXT and GL_BGRA_EXT are part of the EXT_bgra extension.
GL_EXT_convolution: glSeparableFilter2DEXT, GL_SEPARABLE_2D_EXT, GL_CONVOLUTION_FILTER_SCALE_EXT, and GL_CONVOLUTION_FILTER_BIAS_EXT are part of the EXT_convolution extension.
GL_EXT_packed_pixels: GL_UNSIGNED_BYTE_3_3_2_EXT, GL_UNSIGNED_BYTE_2_3_3_REV_EXT, GL_UNSIGNED_SHORT_5_6_5_EXT, GL_UNSIGNED_SHORT_5_6_5_REV_EXT, GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_4_4_4_4_REV_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT, GL_UNSIGNED_SHORT_1_5_5_5_REV_EXT, GL_UNSIGNED_INT_8_8_8_8_EXT, GL_UNSIGNED_INT_8_8_8_8_REV_EXT, GL_UNSIGNED_INT_10_10_10_2_EXT, and GL_UNSIGNED_INT_2_10_10_10_REV_EXT are part of the EXT_packed_pixels extension.

ERRORS

GL_INVALID_ENUM is generated if target is not GL_CONVOLUTION_2D_EXT.

GL_INVALID_ENUM is generated if internalformat 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 glGetConvolutionParameterEXT using target GL_CONVOLUTION_2D_EXT and name GL_MAX_CONVOLUTION_WIDTH_EXT.

GL_INVALID_VALUE is generated if height is less than zero or greater than the maximum supported value. This value may be queried with glGetConvolutionParameterEXT using target GL_CONVOLUTION_2D_EXT and name GL_MAX_CONVOLUTION_HEIGHT_EXT.

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 glSeparableFilter2DEXT is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

glGetConvolutionParameterEXT
glGetSeparableFilterEXT