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379 lines
18 KiB
379 lines
18 KiB
Name
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HP_image_transform
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Name Strings
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GL_HP_image_transform
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Version
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$Date: 1995/09/09 21:55:00 $ $Revision: 1.11 $
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Number
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66
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Dependencies
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EXT_texture is required
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EXT_convolution affects the definition of this extension
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SGI_color_table is required
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Overview
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This extension provides support for scaling, rotation, and translation
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of two-dimensional pixel rectangles at a fixed location in the pixel
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transfer process. The 2D image transformation attributes are specified
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as individual values so that that implementations may easily detect
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scaling and rotation values that lend themselves to optimization. 2D
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image transformation occurs immediately after the post-convolution color
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table stage of the pixel pipeline. This extension also defines a color
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table that is applied immediately after the image transformation operation.
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New Procedures and Functions
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void ImageTransformParameteriHP(enum target,
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enum pname,
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const int param)
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void ImageTransformParameterfHP(enum target,
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enum pname,
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const float param)
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void ImageTransformParameterivHP(enum target,
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enum pname,
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const int* params)
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void ImageTransformParameterfvHP(enum target,
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enum pname,
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const float* params)
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These routines are used to set image transformation attributes.
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The only allowable value for <target> at this time is
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IMAGE_TRANSFORM_2D_HP. Allowable values for <pname> include:
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IMAGE_SCALE_X_HP, IMAGE_SCALE_Y_HP, IMAGE_ROTATE_ANGLE_HP,
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IMAGE_ROTATE_ORIGIN_X_HP, IMAGE_ROTATE_ORIGIN_Y_HP,
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IMAGE_TRANSLATE_X_HP, IMAGE_TRANSLATE_Y_HP, IMAGE_MAG_FILTER_HP,
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IMAGE_MIN_FILTER_HP, and IMAGE_CUBIC_WEIGHT_HP.
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void GetImageTransformParameterivHP(enum target,
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enum pname,
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const int* params)
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void GetImageTransformParameterfvHP(enum target,
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enum pname,
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const float* params)
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These routines are used to query image transformation attributes.
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The only allowable value for <target> at this time is
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IMAGE_TRANSFORM_2D_HP. Allowable values for <pname> include:
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IMAGE_SCALE_X_HP, IMAGE_SCALE_Y_HP, IMAGE_ROTATE_ANGLE_HP,
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IMAGE_ROTATE_ORIGIN_X_HP, IMAGE_ROTATE_ORIGIN_Y_HP,
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IMAGE_TRANSLATE_X_HP, IMAGE_TRANSLATE_Y_HP, IMAGE_MAG_FILTER_HP,
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IMAGE_MIN_FILTER_HP, and IMAGE_CUBIC_WEIGHT_HP.
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New Tokens
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Accepted by the <pname> parameter of ImageTransformParameteri,
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ImageTransformParameterf, ImageTransformParameteriv,
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ImageTransformParameterfv, GetImageTransformParameteriv and
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GetImageTransformParameterfv:
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IMAGE_SCALE_X_HP
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IMAGE_SCALE_Y_HP
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IMAGE_TRANSLATE_X_HP
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IMAGE_TRANSLATE_Y_HP
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IMAGE_ROTATE_ANGLE_HP
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IMAGE_ROTATE_ORIGIN_X_HP
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IMAGE_ROTATE_ORIGIN_Y_HP
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IMAGE_MAG_FILTER_HP
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IMAGE_MIN_FILTER_HP
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IMAGE_CUBIC_WEIGHT_HP
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Accepted by the <params> parameter of ImageTransformParameteriHP,
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ImageTransformParameterfHP, ImageTransformParameterivHP, and
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ImageTransformParameterfvHP when <pname> is IMAGE_MAG_FILTER_HP
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or IMAGE_MIN_FILTER_HP:
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CUBIC_HP
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Accepted by the <params> parameter of ImageTransformParameteriHP,
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ImageTransformParameterfHP, ImageTransformParameterivHP, and
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ImageTransformParameterfvHP when <pname> is IMAGE_MIN_FILTER_HP:
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AVERAGE_HP
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Accepted by the <cap> parameter of Enable, Disable, and IsEnabled,
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and by the <target> parameter of ImageTransformParameterivHP,
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ImageTransformParameterfvHP, GetImageTransformParameterivHP,
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and GetImageTransformParameterfvHP:
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IMAGE_TRANSFORM_2D_HP
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Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, and
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by the <target> parameter of ColorTableSGI, ColorTableParameterivSGI,
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ColorTableParameterfvSGI, GetColorTableSGI, GetColorTableParameterivSGI,
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and GetColorTableParameterfvSGI:
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POST_IMAGE_TRANSFORM_COLOR_TABLE_HP
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Accepted by the <target> parameter of ColorTableSGI,
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GetColorTableParameterivSGI, and GetColorTableParameterfvSGI:
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PROXY_POST_IMAGE_TRANSFORM_COLOR_TABLE_HP
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Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
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None
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Additions to Chapter 3 of the 1.0 Specification (Rasterization)
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The specification of two-dimensional image transformation operators
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is added to the GL specification in Section 3.6.2, "Pixel Transfer
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Modes." 2D image transformation operators are defined by calling
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ImageTransformParameteriHP, ImageTransformParameterfHP,
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ImageTransformParameterivHP, or ImageTransformParameterfvHP with
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<target> set to IMAGE_TRANSFORM_2D_HP. Parameter values
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IMAGE_SCALE_X_HP and IMAGE_SCALE_Y_HP establish the scaling factors.
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IMAGE_TRANSLATE_X_HP and IMAGE_TRANSLATE_Y_HP set the translation
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factors. IMAGE_ROTATE_ANGLE_HP sets the rotation angle to be
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used, and IMAGE_ROTATE_ORIGIN_X_HP and IMAGE_ROTATE_ORIGIN_Y_HP specify
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the point about which the image is to be scaled and rotated. If the
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specified angle is positive, the rotation will be counterclockwise
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about the specified rotation origin. If the specified angle is
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negative, the rotation will be clockwise about the origin. All
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of these parameters (scale, rotation, translation, rotation origin)
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are specified in terms of the input image's coordinates.
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IMAGE_MAG_FILTER_HP establishes the resampling technique that is to be
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used after the other image transformation operators have been applied
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if the image is deemed to have been magnified. IMAGE_MIN_FILTER_HP
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defines the resampling technique that is to be applied if the image
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is minified by the scaling factors. IMAGE_CUBIC_WEIGHT_HP defines
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the cubic weighting coefficient that is to be used whenever the
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resampling technique is set to CUBIC_HP.
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The operations defined by the image transformation operation are
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added to the GL specification in Section 3.6.3, "Rasterization of
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Pixel Rectangles," immediately following the operations described in
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the EXT_convolution extension and the post convolution color table
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operation that is described in the SGI_color_table extension. Image
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transformation is defined only for pixel rectangles that contain RGBA
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components or depth components at this stage of the pixel processing
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pipeline (color index values may have been converted to RGBA by a
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previous stage). Image transformation is not applied to color index
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or stencil index pixel data.
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When enabled, the image transformation operation uses the current set
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of image transformation parameters to compute a new window coordinate
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for each incoming pixel. Although image transformation parameters
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are specified separately, the scaling, rotation, and translation
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operations are all applied simultaneously (as if the transformation
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was encoded in a matrix and the resulting matrix was applied to each
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incoming pixel coordinate). In the case of 2D image transformation,
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if (Rx,Ry) specifies the rotation origin, the effect of applying the
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2D image transformation operators can be defined as follows. First,
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the image is translated by -Rx in the x direction and -Ry in the y
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direction so that its rotation origin is at the origin of the 2D
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coordinate system. Second, the x and y scaling factors are
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applied, causing the image to be scaled as specified in x and y.
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Third, the rotation angle is applied, causing the image to be rotated
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about the origin by the specified angle. Next, the image is translated
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by Rx in the x direction and Ry in the y direction. Finally, the
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scaled and rotated image is translated by the specified translation
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factors. Resampling occurs after the scaling/rotation/translation
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operations have been applied.
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The RGBA or depth value for each location is left unmodified by the image
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transformation. Since multiple input pixels can be mapped into a single
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output pixel (minification of input image), or since output pixels might
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not have any input pixels mapped to them (magnification of input image),
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some method of resampling is required. The resampling method to be
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used when the image is magnified is specified by calling
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ImageTransformParameteri, ImageTransformParameterf,
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ImageTransformParameteriv, or ImageTransformParameterfv with <pname>
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set to IMAGE_MAG_FILTER_HP and <params> set to NEAREST, LINEAR, or CUBIC_HP.
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The resampling method to be used when the image is minified is specified
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by calling ImageTransformParameteri, ImageTransformParameterf,
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ImageTransformParameteriv, or ImageTransformParameterfv with <pname>
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set to IMAGE_MIN_FILTER_HP and <params> set to NEAREST, LINEAR, CUBIC_HP,
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or AVERAGE_HP. If the resampling method is NEAREST, each output pixel will
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have the value of the input pixel whose transformed coordinate value is
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nearest (in Manhattan distance). If the resampling method is LINEAR, each
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output pixel will have a value that is the weighted average of the four input
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pixels whose transformed coordinate values are nearest.
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If the resampling method is CUBIC_HP, each output pixel will have a value
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that is affected by the 16 input pixels whose transformed coordinate
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values are nearest. The 16 input pixels will be used to perform a cubic
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spline interpolation to determine the value of the output pixel. The
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cubic weight factor is a floating point value that is applied to the
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cubic interpolation in the manner described in "Digital Image Warping"
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by George Wolberg (IEEE Computer Society Press, ISBN 0-8186-8944-7).
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Visually pleasing cubic weighting values are typically in the
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range [-1,0]. The values -1.0 and -0.5 are most commonly used.
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For the purpose of performing bicubic interpolation along the outer
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edge of the image, the outermost one pixel edge of the image is
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duplicated prior to performing the interpolation along the edges.
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If the resampling method is AVERAGE_HP, the values of all of the input
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pixels that contribute to the final output pixel will be averaged to
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determine the final output pixel value.
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The operation of the POST_IMAGE_TRANSFORM_COLOR_TABLE is added to the GL
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Specification in section 3.6.3, "Rasterization of Pixel Rectangles".
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This color table behaves in the manner described in the SGI_color_table
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extension, and it is located immediately after the image transformation
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operation. This color table can be enabled or disabled separately from
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the image transformation operation by calling Enable or Disable with
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POST_IMAGE_TRANSFORM_COLOR_TABLE. It can be modified using the procedures
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defined in the SGI_color_table extension. The proxy version of this table
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can be set or queried by using a target value of
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PROXY_POST_IMAGE_TRANSFORM_COLOR_TABLE.
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Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
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and the Frame Buffer)
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The operation of image transformation during pixel copy and query
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operations is identical to the operation during pixel drawing and
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texture image definition. The image transformation operation occurs
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immediately after the operations described by EXT_convolution and
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the post-convolution color table described by SGI_color_table, which
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follow section 4.3.2 (Reading Pixels) of the GL Specification.
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Additions to Chapter 5 of the 1.0 Specification (Special Functions)
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GetImageTransformParameterivHP, and GetImageTransformParameterfvHP
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are not included in display lists, but are instead executed immediately.
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Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
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Integer and floating point query functions GetImageTransformParameterivHP
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and GetImageTransformParameterfvHP are provided. <target> must be
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IMAGE_TRANSFORM_2D_HP. <pname> is one of IMAGE_SCALE_X_HP,
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IMAGE_SCALE_Y_HP, IMAGE_TRANSLATE_X_HP, IMAGE_TRANSLATE_Y_HP,
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IMAGE_ROTATE_ANGLE_HP, IMAGE_ROTATE_ORIGIN_X_HP,
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IMAGE_ROTATE_ORIGIN_Y_HP, IMAGE_MAG_FILTER_HP, IMAGE_MIN_FILTER_HP,
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or IMAGE_CUBIC_WEIGHT_HP. The value of the specified parameter is
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returned in <params>.
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Additions to the GLX Specification
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None
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Dependencies on EXT_texture
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EXT_texture is required. This extension builds on the notion of
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internal image format, which is defined by EXT_texture.
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Dependencies on EXT_convolution
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None, except that image transformation follows the convolution
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operation (and its scale and bias). If the post-convolution color
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table is supported, the image transformation operation will occur
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immediately after the post-convolution color table operation. If
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convolution is not supported, the location with respect to all other
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pixel operations remains the same.
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Dependencies on SGI_color_table
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SGI_color_table is required. This extension builds on the notion of
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color lookup tables at various locations in the pixel processing pipeline.
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This extension adds another table to the list specified by SGI_color_table.
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This new table can be manipulated using the procedures defined by
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SGI_color_table.
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Errors
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INVALID_ENUM is generated if ImageTransformParameteriHP,
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ImageTransformParameterfHP, ImageTransformParameterivHP,
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ImageTransformParameterfvHP, GetImageTransformParameterivHP,
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or GetImageTransformParameterfvHP is called with <target> set to
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a value other than IMAGE_TRANSFORM_2D_HP.
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INVALID_ENUM is generated if GetImageTransformParameterivHP or
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GetImageTransformParameterfvHP is called with <pname> set to
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IMAGE_MAG_FILTER_HP and <params> is not one of NEAREST, LINEAR,
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or CUBIC_HP.
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INVALID_ENUM is generated if GetImageTransformParameterivHP or
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GetImageTransformParameterfvHP is called with <pname> set to
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IMAGE_MIN_FILTER_HP and <params> is not one of NEAREST, LINEAR,
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CUBIC_HP, or AVERAGE_HP.
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INVALID_VALUE is generated if ImageTransformParameteriHP,
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ImageTransformParameterfHP, ImageTransformParameterivHP, or
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ImageTransformParameterfvHP is called with <pname> set to
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IMAGE_CUBIC_WEIGHT_HP and <params> is a value outside of
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the range [0,1].
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INVALID_OPERATION is generated if ImageTransformParameteriHP,
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ImageTransformParameterfHP, ImageTransformParameterivHP,
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ImageTransformParameterfvHP, GetImageTransformParameterivHP,
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or GetImageTransformParameterfvHP is called between execution of
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Begin and the corresponding execution of End.
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New State
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Initial
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Get Value Get Command Type Value Attrib
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--------- ----------- ---- ------- ------
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IMAGE_TRANSFORM_2D_HP IsEnabled B False pixel/enable
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IMAGE_SCALE_X_HP GetImageTransformParameterf R 1 pixel
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IMAGE_SCALE_Y_HP GetImageTransformParameterf R 1 pixel
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IMAGE_TRANSLATE_X_HP GetImageTransformParameterf R 0 pixel
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IMAGE_TRANSLATE_Y_HP GetImageTransformParameterf R 0 pixel
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IMAGE_ROTATE_ANGLE_HP GetImageTransformParameterf R 0 pixel
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IMAGE_ROTATE_ORIGIN_X_HP GetImageTransformParameterf R 0 pixel
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IMAGE_ROTATE_ORIGIN_Y_HP GetImageTransformParameterf R 0 pixel
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IMAGE_MAG_FILTER_HP GetImageTransformParameteri Z3 NEAREST pixel
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IMAGE_MIN_FILTER_HP GetImageTransformParameteri Z4 NEAREST pixel
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IMAGE_CUBIC_WEIGHT_HP GetImageTransformParameterf R -1 pixel
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POST_IMAGE_TRANSFORM_COLOR_TABLE_HP IsEnabled B False pixel/enable
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POST_IMAGE_TRANSFORM_COLOR_TABLE_HP GetColorTableHP 3 x I empty -
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New Implementation Dependent State
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None
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Issues
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What is the behavior of ReadPixels when the image transformation
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is enabled? One suggestion is to assume that the specified width
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and height of the region being read are used to define the size
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of the 2D array in host memory in which the pixel values are to
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be written. Any pixels that would be written outside of this region
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would be clipped. Why would anyone want to rotate/scale during
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a readback operation anyway? Another suggestion is that image
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transformation is ignored during readback, but this makes it
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different than the other pixel transfer operations.
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Notes
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I originally wrote this extension to utilize an image transformation
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matrix that worked the same way the other OpenGL matrices worked.
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However, we found that we could not easily extract the rotation and
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scaling information and use it to select optimized software routines
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for special cases like integer zoom and 90 degree rotations.
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Consequently, I've reverted back to specifying the image transformation
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parameters individually and the image transformation operation
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in a more rigid way.
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I would rather have separate state setting calls for each of the
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2D image transformation parameters. However, SGI's convolution,
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color table, and histogram extension all use FooParameter{i,f}v calls
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to set the state. I've mimicked their API for three reasons:
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1. For consistency with those extensions
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2. To maximize the likelihood of industry acceptance
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of this extension
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3. To allow for the possibility of 1D and 3D image
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transforms at a future time.
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I have not excluded the ability to scale, rotate, and translate
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depth component values. I thought that image transformation might
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be useful when the <format> was DEPTH_COMPONENT (i.e., reading or writing
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depth buffer values). In this case, the "image" will have x and y values
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that define the pixel locations, and depth (z) values instead of color
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values. The depth values will end up being treated as a single channel
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image. This capability might be necessary if you have a depth buffer
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associated with an image that you want to remain registered as it is
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stored in the frame buffer.
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