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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 Operationsand 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
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