skia / external / github.com / KhronosGroup / OpenGL-Registry / 01ac568838ce3a93385d885362e3ddc7bca54b08 / . / extensions / SGIX / SGIX_decimation.txt

Name | |

SGIX_decimation | |

Name Strings | |

GL_SGIX_decimation | |

Version | |

$Date: 1997/07/18 00:49:00 $ $Revision: 1.4 $ | |

Number | |

125 | |

Dependencies | |

EXT_convolution affects the definition of this extension | |

SGI_color_table affects the definition of this extension | |

Overview | |

This extension adds a decimation operation to the pixel transfer | |

path. | |

Decimation occurs after convolution and prior to the post-convolution | |

color table. | |

The operation is controlled by two positive integer parameters, stepx | |

and stepy, that specify the decimation step size in the x and y | |

directions, respectively. During a pixel transfer, the decimation | |

operation passes only those pixels which are at a position (i*stepx, | |

j*stepy), for integers (i, j), relative to the bottom left corner of | |

the image that is being transferred. All other pixels are discarded. | |

Decimation is applied to the image that results from convolution, | |

which may differ in size from the source image if convolution is | |

enabled. | |

By default, stepx and stepy are both 1. | |

Issues | |

* This spec allows for future extension to 3D decimation. | |

* What is a reasonable minimum maximum decimation step that we should | |

enforce? Two is probably sufficient. | |

* Future extensions that redefine the convolution operation at the border | |

of an image may affect this specification. | |

* Decimation doesn't apply to bitmaps because they are not affected | |

by the PixelTransfer state. This is probably best. | |

* Decimation is related to interlacing, as defined in the | |

SGIX_interlace extension. In fact, it provides the inverse of | |

interlacing. It appears useful to be able to enable decimation and | |

interlacing on the same transfer. Interactions between these | |

two extensions should be examined further. | |

New Procedures and Functions | |

None | |

New Tokens | |

Accepted by the <pname> parameter of glPixelTransferf, | |

glPixelTransferi, GetBooleanv, GetIntegerv, | |

GetFloatv, and GetDoublev: | |

DECIMATION_X_SGIX 0xXXXX | |

DECIMATION_Y_SGIX 0xXXXX | |

Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, | |

GetFloatv, and GetDoublev: | |

MAX_DECIMATION_X_SGIX 0xXXXX | |

MAX_DECIMATION_Y_SGIX 0xXXXX | |

Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation) | |

None | |

Additions to Chapter 3 of the 1.0 Specification (Rasterization) | |

The specification of the decimation operation is added to the GL | |

Specification in section 3.6.2, "Pixel Transfer Modes." | |

The decimation operation is added to the GL Specification in section | |

3.6.3, "Rasterization of Pixel Rectangles, immediately following the | |

operations described in EXT_convolution, and prior to the | |

post-convolution color table operation that is described in the | |

SGI_color_table extension. | |

Decimation operates on the image of pixels resulting from the | |

convolution stage of the pixel transfer path. If stepx and stepy are | |

the current decimation step parameters, then the decimation | |

operation passes only those pixels which are at a position (i*stepx, | |

j*stepy), for integers (i, j), relative to the bottom left corner of | |

the image. All other pixels are discarded. If the image size prior | |

to decimation is (nx, ny), where nx >= 1 and ny >= 1, then its size | |

after decimation will be (floor((nx-1)/stepx) + 1, | |

floor((ny-1)/stepy) + 1)). | |

Decimation is applied to the image that results from convolution, | |

which may differ in size from the source image if convolution is | |

enabled. | |

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. | |

If this extension is implemented, decimation is always active, and is | |

applied to any pixel transfer, regardless of the command used to | |

generate it. (There is no enable or disable of decimation.) | |

The x and y decimation parameters are specified by calling | |

PixelTransfer with <pname> set to DECIMATION_X_SGIX, and | |

DECIMATION_Y_SGIX, respectively. Each parameter value must be a | |

positive integer less than or equal to MAX_DECIMATION_X_SGIX and | |

MAX_DECIMATION_Y_SGIX, respectively. | |

Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations | |

and the Framebuffer) | |

The operation of decimation during pixel copy and query operations is | |

identical to the operation during pixel drawing and texture image | |

definition. This operation occurs immediately after the operations | |

described by EXT_convolution, and prior to the post-convolution color | |

table operation that is described in the SGI_color_table extension, | |

which follow section 4.3.2 (Reading Pixels) of the GL Specification. | |

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) | |

The x decimation step parameter is queried using GetIntegerv with | |

<pname> set to DECIMATION_X_SGIX. | |

The y decimation step parameter is queried using GetIntegerv with | |

<pname> set to DECIMATION_Y_SGIX. | |

The maximum allowed x decimation step parameter is queried using | |

GetIntegerv with <pname> set to MAX_DECIMATION_X_SGIX. | |

The maximum allowed y decimation step parameter is queried using | |

GetIntegerv with <pname> set to MAX_DECIMATION_Y_SGIX. | |

Additions to the GLX Specification | |

None | |

GLX Protocol | |

None | |

Dependencies on EXT_convolution | |

The decimation operation follows the convolution operation (and its | |

scale and bias). If convolution is not supported, the location of | |

the decimation operation with respect to all other pixel operations | |

remains the same. | |

Dependencies on SGI_color_table | |

The decimation operation precedes the post-convolution color table | |

operation. If the post-convolution color table operation is not | |

supported, the location of the decimation operation with respect to | |

all other pixel operations remains the same. | |

Errors | |

INVALID_VALUE is generated if PixelTransfer is called with parameter | |

<pname> equal to DECIMATION_X_SGIX and parameter <param> less | |

than 1 or greater than MAX_DECIMATION_X_SGIX as queried using | |

GetIntegerv with <pname> MAX_DECIMATION_X_SGIX. | |

INVALID_VALUE is generated if PixelTransfer is called with parameter | |

<pname> equal to DECIMATION_Y_SGIX and parameter <param> less | |

than 1 or greater than MAX_DECIMATION_Y_SGIX as queried using | |

GetIntegerv with <pname> MAX_DECIMATION_Y_SGIX. | |

New State | |

Get Value Get Command Type Initial Value Attribute | |

--------- ----------- ---- ------------- --------- | |

DECIMATION_X_SGIX GetIntegerv Z+ 1 pixel | |

DECIMATION_Y_SGIX GetIntegerv Z+ 1 pixel | |

New Implementation Dependent State | |

Get Value Get Command Type Minimum Value | |

--------- ----------- ---- ------------- | |

MAX_DECIMATION_X_SGIX GetIntegerv Z+ 2 | |

MAX_DECIMATION_Y_SGIX GetIntegerv Z+ 2 | |