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Manual Reference Pages  - GLCONVOLUTIONFILTER2D (3G)

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glConvolutionFilter2D - define a two-dimensional convolution filter

CONTENTS

C Specification
Parameters
Description
Notes
Errors
Associated Gets
See Also

void glConvolutionFilter2D( GLenum target,

                          GLenum internalformat,
                          GLsizei width,
                          GLsizei height,
                          GLenum format,
                          GLenum type,
                          const GLvoid *image )

target	Must be  GL_CONVOLUTION_2D.
internalformat	The internal 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 image.
height	The height of the pixel array referenced by image.
format	The of the pixel data in image. The allowable values are  GL_RED,  GL_GREEN,  GL_BLUE,  GL_ALPHA,  GL_RGB,  GL_BGR,  GL_RGBA,  GL_BGRA,  GL_LUMINANCE, and  GL_LUMINANCE_ALPHA.
type	The type of the pixel data in 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 a two-dimensional array of pixel data that is processed to build the convolution filter kernel.

 glConvolutionFilter2D builds a two-dimensional convolution filter kernel from an array of pixels.

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

The R, G, B, and A components of each pixel are next scaled by the four 2D  GL_CONVOLUTION_FILTER_SCALE parameters and biased by the four 2D  GL_CONVOLUTION_FILTER_BIAS parameters. (The scale and bias parameters are set by  glConvolutionParameter using the  GL_CONVOLUTION_2D 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 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 (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 They form a two-dimensional filter kernel image indexed with coordinates i and j such that i starts at zero and increases from left to right, and j starts at zero and increases from bottom to top. Kernel location i,j is derived from the Nth 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 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.

 glConvolutionFilter2D is present only if  GL_ARB_imaging is returned when  glGetString is called with an argument of  GL_EXTENSIONS.

 GL_INVALID_ENUM is generated if target is not  GL_CONVOLUTION_2D.

 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  glGetConvolutionParameter using target  GL_CONVOLUTION_2D and name  GL_MAX_CONVOLUTION_WIDTH.

 GL_INVALID_VALUE is generated if height is less than zero or greater than the maximum supported value. This value may be queried with  glGetConvolutionParameter using target  GL_CONVOLUTION_2D and name  GL_MAX_CONVOLUTION_HEIGHT.

 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  glConvolutionFilter2D is executed between the execution of  glBegin and the corresponding execution of  glEnd.

 GL_INVALID_OPERATION is generated if height 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 height 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.

 glGetConvolutionParameter,  glGetConvolutionFilter

 glConvolutionFilter1D(3G),  glSeparableFilter2D(3G),  glConvolutionParameter(3G),  glPixelTransfer(3G)

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