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Manual Reference Pages  - GLCOPYCONVOLUTIONFILTER2D (3G)

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glCopyConvolutionFilter2D - copy pixels into a two-dimensional convolution filter

CONTENTS

C Specification
Parameters
Description
Notes
Errors
Associated Gets
See Also

void glCopyConvolutionFilter2D( GLenum target,

                              GLenum internalformat,
                              GLint x,
                              GLint y,
                              GLsizei width,
                              GLsizei height )

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.
x, y	The window space coordinates of the lower-left coordinate of the pixel array to copy.
width	The width of the pixel array to copy.
height	The height of the pixel array to copy.

 glCopyConvolutionFilter2D defines a two-dimensional convolution filter kernel with pixels from the current  GL_READ_BUFFER (rather than from main memory, as is the case for  glConvolutionFilter2D).

The screen-aligned pixel rectangle with lower-left corner at (x, y), width width and height height is used to define the convolution filter. If any pixels within this region are outside the window that is associated with the GL context, the values obtained for those pixels are undefined.

The pixels in the rectangle are processed exactly as if  glReadPixels had been called with format set to RGBA, but the process stops just before final conversion. 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

Pixel ordering is such that lower x screen coordinates correspond to lower i filter image coordinates, and lower y screen coordinates correspond to lower j filter image coordinates.

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.

 glCopyConvolutionFilter2D 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_OPERATION is generated if  glCopyConvolutionFilter2D is executed between the execution of  glBegin and the corresponding execution of  glEnd.

 glGetConvolutionParameter,  glGetConvolutionFilter

 glConvolutionFilter2D(3G),  glConvolutionParameter(3G),  glPixelTransfer(3G)

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