glconvolutionfilter2dext - Man Page
glConvolutionFilter2DEXT(3G) OpenGL Reference glConvolutionFilter2DEXT(3G)
NAME
glConvolutionFilter2DEXT - define a two-dimensional convolution filter
C SPECIFICATION
void glConvolutionFilter2DEXT( GLenum target,
GLenum internalformat,
GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const GLvoid *image )
PARAMETERS
target Must be GL_CONVOLUTION_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 width of the pixel array referenced by image.
height The height of the pixel array referenced by image.
format The format of the pixel data in image. The allowable
values are GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB,
GL_RGBA, and GL_ABGR_EXT.
type The type of the pixel data in image. 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_SHORT_4_4_4_4_EXT,
GL_UNSIGNED_SHORT_5_5_5_1_EXT,
GL_UNSIGNED_INT_8_8_8_8_EXT, and
GL_UNSIGNED_INT_10_10_10_2_EXT.
image Pointer to a two-dimensional array of pixel data that is
processed to build the convolution filter kernel.
DESCRIPTION
glConvolutionFilter2DEXT 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_EXT parameters and biased by the four 2D
Page 1
glConvolutionFilter2DEXT(3G) OpenGL Reference glConvolutionFilter2DEXT(3G)
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 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_LUMINANCE R
GL_LUMINANCE_ALPHA A R
GL_INTENSITY_EXT 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 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_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.
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.
Page 2
glConvolutionFilter2DEXT(3G) OpenGL Reference glConvolutionFilter2DEXT(3G)
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 glConvolutionFilter2DEXT is executed
between the execution of glBegin and the corresponding execution of
glEnd.
If type is set to GL_UNSIGNED_BYTE_3_3_2_EXT,
GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT and the
EXT_packed_pixels extension is not supported then a GL_INVALID_ENUM error
is generated.
ASSOCIATED GETS
glGetConvolutionParameterEXT, glGetConvolutionFilterEXT
MACHINE DEPENDENCIES
On RealityEngine, RealityEngine2, and VTX systems convolution may not be
used in the following circumstances:
1. When rendering to pixmaps.
2. When fragment processing (texturing, depth buffering, alpha
testing, multisampling, fog) is enabled.
3. When histogramming or minmax is enabled.
4. When either of the pixel zoom factors has a value other than 1.0
or -1.0.
In these cases, glDrawPixels and glCopyPixels report a
GL_INVALID_OPERATION error and do not transfer any pixels.
Loading a convolution filter with some combinations of pixel transfer
modes may be unreliable on InfiniteReality systems. Straightforward
transfers are known to work, though. The remaining problems will be
fixed in the next release.
SEE ALSO
glConvolutionFilter1DEXT, glSeparableFilter2DEXT,
glConvolutionParameterEXT, glEnable with parameter GL_CONVOLUTION_2D_EXT,
glPixelTransfer.
Page 3