XXX - Not complete.

Name

    SGIX_resample

Name Strings

    GL_SGIX_resample

Version

    Last Modified Date: January 27, 2015
    Revision: 2

Number

    212

Dependencies

	SGIX_subsample affects the definition of this extension
	EXT_texture3D affects the definition of this extension
	EXT_subtexture affects the definition of this extension
	EXT_histogram affects the definition of this extension
	EXT_convolution affects the definition of this extension
	SGI_color_table affects the definition of this extension

Overview

	This extension enhances the unpacking resampling capabilities
	of the SGIX_subsample extension.

	When pixel data is received from the client and an unpacking
	upsampling mode other than PIXEL_SUBSAMPLE_RATE_4444_SGIX is
	specified, the upsampling is performed via one of two methods:
	RESAMPLE_REPLICATE_SGIX, RESAMPLE_ZERO_FILL_SGIX.
	Replicate and zero fill are provided to
	give the application greatest performance and control over the
	filtering process.

	However, when pixel data is read back to the client and a
	packing downsampling mode other than PIXEL_SUBSAMPLE_RATE_4444_SGIX
	is specified, downsampling is
	performed via simple component decimation (point sampling). That is,
	only the RESAMPLE_DECIMATE_SGIX is valid.


Issues

	* this spec omits the packing downsampling mode.  But I think
	we will have to address it at some point, so I'm adding the
	RESAMPLE_DECIMATE_SGIX as another tag to complement the unpacking
	resample modes.

        * In the public Khronos spec files and headers, these values
          used to be used for some of the tokens: 

            #define GL_PACK_RESAMPLE_SGIX        0x842C 
            #define GL_UNPACK_RESAMPLE_SGIX      0x842D 
            #define GL_RESAMPLE_REPLICATE_SGIX   0x842E 
            #define GL_RESAMPLE_ZERO_FILL_SGIX   0x842F 
            #define GL_RESAMPLE_DECIMATE_SGIX    0x8430 
               
          These values corresponded to the internal SGI spec files and
          (probably) to what was shipped on SGI IRIX systems supporting this
          extension, but the spec was always inconsistent with these values.
          Since SGI is long out of the graphics business, in order to reduce
          incompatibility between tools pulling from the Khronos spec file
          and tools pulling from the extension spec, the spec file has been
          changed to match the extension.

New Procedures and Functions

	None.

New Tokens

	Accepted by the <pname> parameter of PixelStoref, PixelStorei,
	GetBooleanv, GetIntegerv, GetFloatv and GetDoublev:

		PACK_RESAMPLE_SGIX		0x842E
		UNPACK_RESAMPLE_SGIX		0x842F


	Accepted by the <param> parameter of PixelStoref and
	PixelStorei when the <pname> parameter is UNPACK_RESAMPLE_SGIX:

		RESAMPLE_REPLICATE_SGIX		0x8433
		RESAMPLE_ZERO_FILL_SGIX		0x8434

	Accepted by the <param> parameter of PixelStoref and
	PixelStorei when the <pname> parameter is PACK_RESAMPLE_SGIX:

		RESAMPLE_DECIMATE_SGIX		0x8430


Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation)

	None.

Additions to Chapter 3 of the 1.1 Specification (Rasterization)

	3.6.1 Pixel Storage Modes

	The following is added to Table 3.1:

	Parameter Name		Type	    Initial Value		Valid Range
	--------------		----	    -------------		-----------
	UNPACK_RESAMPLE_SGIX	integer     RESAMPLE_REPLICATE_SGIX	RESAMPLE_REPLICATE_SGIX
									RESAMPLE_ZERO_FILL_SGIX

	PACK_RESAMPLE_SGIX	integer     RESAMPLE_DECIMATE_SGIX	RESAMPLE_DECIMATE_SGIX


	3.6.3 Rasterization of Pixel Rectangles


	<In the new section which is inserted before "Conversion to RGB", append>

	Conversion to Uniform Sampling
	------------------------------

	This step is applied only if the PixelStore parameter
	UNPACK_SUBSAMPLE_RATE_SGIX is set to something other than
	PIXEL_SUBSAMPLE_RATE_4444_SGIX. If UNPACK_SUBSAMPLE_RATE_SGIX is set to
	PIXEL_SUBSAMPLE_RATE_2424_SGIX or PIXEL_SUBSAMPLE_RATE_4242_SGIX then
	the number of components per pixel is increased from two to three.
	After upsampling, the data is treated as though it were RGB.  When
	this step is carried out the operation is controlled by the value
	of the PixelStore parameter UNPACK_RESAMPLE_SGIX.

	If UNPACK_RESAMPLE_SGIX is set to  RESAMPLE_REPLICATE_SGIX then the first
	component of the ith resulting pixel in a row is taken from the
	first component of input pixel 2*floor(i/2). The second
	component is taken from ith pixel. The third component is taken
	from the first component of input pixel 2*floor(i/2)+1. In the
	4224 case, the fourth component is taken from the third
	component of each input pixel. This process is fully described
	in the SGIX_subsample spec.

	If the PixelStore parameter UNPACK_RESAMPLE_SGIX is set to
	RESAMPLE_ZERO_FILL_SGIX then derived components are zeroed. Note that
	subsampled components are co-sited with even numbered pixels,
	and the odd numbered pixels produced have the zeroed components:

	2424:

	<L0,A0>      <L1,A1>	  <L2,A2>      <L3,A3>
	<Cb0,Y0>     <Cr0,Y1>	  <Cb2,Y2>    <Cr2, Y3>
	  |  |	      |   |	   |   |	|   |
	  |  |	o-----o   |	   |   |  o-----o   |
	  |  |	|	  |	   |   |  |	    |
	  |  |	|    0.0  | 0.0    |   |  |    0.0  | 0.0
	  |  |	|     |   |  |	   |   |  |	|   |  |
	  V  V	V     V   V  V	   V   V  V	V   V  V
	<Cb0,Y0,Cr0> <Cb0,Y1,Cr0> <Cb2,Y2,Cr2> <Cb2,Y3,Cr2>
	< R0,G0,B1 > < R0,G1,B1 > < R2,G2,B3 > < R2,G3,B3 >

	4242:
	< A0,L0>      <A1,L1 >	   <A2,L2 >    < A3,L3 >
	<Y0,Cb0>      <Y1,Cr0>	   <Y2,Cb2>	<Y3,Cr2>
	  |  |	       |   |	    |	|	 |   |
	  \ /	     __\__/	    \ /        __\__/
	   X	 ___/	\	     X	   ___/   \
	  / \	/    0.0 \  0.0     / \   /    0.0 \  0.0
	  |  |	|     |   |  |	    |  |  |	|   |  |
	  V  V	V     V   V  V	    V  V  V	V   V  V
	<Cb0,Y0,Cr0> <Cb0,Y1,Cr0> <Cb2,Y2,Cr2> <Cb2,Y3,Cr2>
	< R0,G0,B1 > < R0,G1,B1 > < R2,G2,B3 > < R2,G3,B3 >


	Note that the <width> parameter to DrawPixels should be even,
	as should the value of UNPACK_SKIP_PIXELS, and
	UNPACK_ROW_LENGTH. If any of these are odd then the error
	INVALID_OPERATION is issued.


Additions to Chapter 4 of the 1.1 Specification (Per-Fragment
Operations and the Frame Buffer)

	None.

Additions to Chapter 5 of the 1.1 Specification (Special Functions)

	None.

Additions to Chapter 6 of the 1.1 Specification (State and State Requests)

	XXX

Additions to the GLX Specification


Errors

	XXX


New State

    Get Value			Get Command			Type		Initial Value		Attribute
    ---------			-----------			----		-------------		---------
    UNPACK_RESAMPLE_SGIX	GetIntegerv			Z4		RESAMPLE_REPLICATE_SGIX client
    PACK_RESAMPLE_SGIX		GetIntegerv			Z4		RESAMPLE_REPLICATE_SGIX client

New Implementation Dependent State

	None.

Revision History

    Revision 1, July 27, 1999 - SGI internal revision #4.

    Revision 2, January 27, 2015 - note that Khronos spec file values from
    enums have been changed to match the extension spec (Khronos internal
    bug 12653).