glConvolutionFilter2D — define a two-dimensional convolution filter
void glConvolutionFilter2D( | GLenum | target, |
| GLenum | internalformat, | |
| GLsizei | width, | |
| GLsizei | height, | |
| GLenum | format, | |
| GLenum | type, | |
| const GLvoid * | data); |
target
Must be GL_CONVOLUTION_2D.
internalformat
The internal format 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 data.
height
The height of the pixel array referenced by data.
format
The format of the pixel data in data.
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 data.
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.
dataPointer 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
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:
| 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
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 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 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_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.
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