Name
HP_convolution_border_modes
Name Strings
GL_HP_convolution_border_modes
Version
$Date: 1995/09/09 10:13:00 $ $Revision: 1.2 $
Number
67
Dependencies
EXT_convolution is required
Overview
This extension provides some additional border modes for the
EXT_convolution extension.
New Procedures and Functions
None
New Tokens
Accepted by the <param> parameter of ConvolutionParameteriEXT,
and ConvolutionParameterfEXT, and by the <params> parameter of
ConvolutionParameterivEXT and ConvolutionParameterfvEXT, when the
<pname> parameter is CONVOLUTION_BORDER_MODE_EXT:
IGNORE_BORDER_HP
CONSTANT_BORDER_HP
WRAP_BORDER_HP
Accepted by the <pname> parameter of ConvolutionParameterivEXT,
ConvolutionParameterfvEXT, GetConvolutionParameterivEXT, and
GetConvolutionParameterfvEXT:
CONVOLUTION_BORDER_COLOR_HP
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
None
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
The description of the convolution border mode is replaced with
the following:
The convolution border mode for a specific convolution filter is
specified using ConvolutionParameteriEXT with the <target>
parameter set to the name of the filter, the <pname> parameter
set to CONVOLUTION_BORDER_MODE_EXT, and <param> set to one of
REDUCE_EXT, IGNORE_BORDER_HP, CONSTANT_BORDER_HP, or
WRAP_BORDER_HP.
The width and height of source images convolved with border mode
REDUCE_EXT are reduced by Wf-1 and Hf-1, respectively. If this
reduction would generate a resulting image with zero or negative
width and/or height, the output is simply null, with no error
generated. The coordinates of the image that results from a
convolution with border mode REDUCE_EXT are zero through Ws-Wf
in width, and zero through Hs-Hf in height. In cases where
errors can result from the specification of invalid image
dimensions, it is these resulting dimensions that are tested,
not the dimensions of the source image. (A specific example is
TexImage1D and TexImage2D, which specify constraints for image
dimensions. Even if TexImage1D or TexImage2D is called with a
null pixel pointer, the dimensions of the resulting texture image
are those that would result from the convolution of the specified
image.)
For the remaining border modes, we define Cw = floor(Wf / 2)
and Ch = floor(Hf / 2). The coordinates (Cw, Ch) define the
center of the convolution filter.
If the convolution border mode is IGNORE_BORDER_HP, the output
image has the same dimensions as the source image. The convolution
filter is moved around the source image so that its center passes
over every pixel in the source image. At each location, the sum of
products is computed and the result is written in the destination
image at the location that corresponds to the pixel location where
the convolution filter is centered. However, the sum of products
is not computed for any pixel where the convolution filter extends
beyond one of the edges of the source image. Instead, for these
locations, the pixel value from the source image is copied to
the destination image.
The convolution border mode CONSTANT_BORDER_HP is identical to
IGNORE_BORDER_HP except that for each pixel where the convolution
filter extends beyond one of the edges of the source image, a value
equal to the current border color will be used as the value for
the source image. The current convolution border color is set by
calling ConvolutionParameterivEXT or ConvolutionParameterfvEXT with
<pname> set to CONVOLUTION_BORDER_COLOR_HP and <params> containing
four values that comprise the RGBA color to be used as the image
border. Integer color components are interpreted linearly such that
the most positive integer maps to 1.0, and the most negative integer
maps to -1.0. Floating point color components are clamped to the
range [0,1] when they are specified.
If the convolution border mode is WRAP_BORDER_HP, the output image
has the same dimensions as the source image, and the source image is
assumed to be continuously wrapped in both x and y directions.
Therefore, source image pixels in the Cw columns on the right edge
are used in the convolution computation for the Cw columns on the
right edge of the image, and vice versa. Similarly, source image
pixels in the Ch rows on the top of the image are used in the
convolution computation for the Ch rows on the bottom of the
image and vice versa.
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Frame buffer)
None
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
None
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
None
Dependencies on EXT_convolution
EXT_convolution is required. This extension adds capability to
the convolution operations defined in that extension.
Errors
INVALID_ENUM is generated if ConvolutionParameterivEXT or
ConvolutionParameterfvEXT parameter <pname> is not
CONVOLUTION_FILTER_SCALE_EXT, CONVOLUTION_FILTER_BIAS_EXT,
CONVOLUTION_BORDER_MODE_EXT, or CONVOLUTION_BORDER_COLOR_HP.
INVALID_ENUM is generated if ConvolutionParameteriEXT,
ConvolutionParameterfEXT, ConvolutionParameterivEXT, or
ConvolutionParameterfvEXT parameter <pname> is
CONVOLUTION_BORDER_MODE_EXT and parameter <params> is
not one of REDUCE_EXT, IGNORE_BORDER_HP, CONSTANT_BORDER_HP,
or WRAP_BORDER_HP.
INVALID_ENUM is generated if GetConvolutionParameterivEXT or
GetConvolutionParameterfvEXT parameter <pname> is not
CONVOLUTION_FILTER_SCALE_EXT, CONVOLUTION_FILTER_BIAS_EXT,
CONVOLUTION_BORDER_MODE_EXT, CONVOLUTION_FORMAT_EXT,
CONVOLUTION_WIDTH_EXT, CONVOLUTION_HEIGHT_EXT,
MAX_CONVOLUTION_WIDTH_EXT, MAX_CONVOLUTION_HEIGHT_EXT,
or CONVOLUTION_BORDER_COLOR_HP.
New State
Initial
Get Value Get Command Type Value Attrib
--------- ----------- ---- ------- ------
CONVOLUTION_BORDER_COLOR_HP GetConvolutionParameterfvHP C (0,0,0,0) pixel
New Implementation Dependent State
None