glConvolutionFilter2D

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

The pixel array specified by width , height , 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 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 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:

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 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 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 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 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_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_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 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 .

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

glGetConvolutionParameter , glGetConvolutionFilter

glConvolutionFilter1D , glSeparableFilter2D , glConvolutionParameter , glPixelTransfer

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/ .