extensions/NV/NV_texture_compression_vtc.txt - external/github.com/KhronosGroup/OpenGL-Registry - Git at Google

 Name

     NV_texture_compression_vtc

 Name Strings

     GL_NV_texture_compression_vtc

 Contact

     Matt Craighead, NVIDIA Corporation (mcraighead 'at' nvidia.com)

 Notice

     Copyright NVIDIA Corporation, 2000, 2001, 2004.

 IP Status

     NVIDIA Proprietary.

 Version

     NVIDIA Date: June 3, 2004
     Version:     4

 Number

     228

 Dependencies

     Written based on the wording of the OpenGL 1.2.1 specification.

     ARB_texture_compression is required.

     EXT_texture_compression_s3tc is required.

     ARB_texture_non_power_of_two interacts with this extension.

 Overview

     This extension adds support for the VTC 3D texture compression
     formats, which are analogous to the S3TC texture compression formats,
     with the addition of some retiling in the Z direction.  VTC has the
     same compression ratio as S3TC and uses 4x4x1, 4x4x2, (4x4x3 when
     non-power-of-two textures are supported), or 4x4x4 blocks.

 Issues

     *   Should the enumerants' (1) values and (2) names be reused from
         the S3TC extension?

         RESOLVED: Yes and yes.  There is such a close correspondence
         between the formats that introducing new values or names would
         serve no purpose.

     *   Should the block alignment restrictions differ in any way from
         the block alignment restrictions in the S3TC extension?

         RESOLVED: No, except for the addition of the Z-direction block
         alignment restriction for CompressedTexSubImage3D, which is
         analogous to the X and Y restrictions.

     *   Should VTC compression work with the ARB_texture_non_power_of_two
         functionality?

         RESOLVED: Yes.  The blockIndex computation works for
         non-power-of-two width, height, and depth dimensions.

         Consider a 31x25x11 3D texture to be stored using VTC.
         The initial 31x25x8 portion of the volume is bricked up using
         VTC with 4x4x4 blocks where the 31x25 dimensions are rounded
         up to 32x28.  Following the expanded 32x28x8 initial volume are
         the final texels arranged as 32x28x3 with 4x4x3 blocks.

 New Procedures and Functions

     None.

 New Tokens

     Accepted by the <internalformat> parameter of TexImage3D and
     CompressedTexImage3DARB and the <format> parameter of
     CompressedTexSubImage2DARB:

         COMPRESSED_RGB_S3TC_DXT1_EXT                   0x83F0
         COMPRESSED_RGBA_S3TC_DXT1_EXT                  0x83F1
         COMPRESSED_RGBA_S3TC_DXT3_EXT                  0x83F2
         COMPRESSED_RGBA_S3TC_DXT5_EXT                  0x83F3

 Additions to Chapter 2 of the OpenGL 1.2.1 Specification (OpenGL Operation)

     None.

 Additions to Chapter 3 of the OpenGL 1.2.1 Specification (Rasterization)

     Modify the paragraph added to the end of the TexSubImage discussion
     (page 123) by EXT_texture_compression_s3tc to say:

     "If the internal format of the texture image being modified is
     COMPRESSED_RGB_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT3_EXT, or COMPRESSED_RGBA_S3TC_DXT5_EXT, the
     texture is stored using one of several S3TC or VTC compressed texture
     image formats.  Such images are easily edited along 4x4 texel
     boundaries, so the limitations on TexSubImage2D, TexSubImage3D,
     CopyTexSubImage2D, and CopyTexSubImage3D parameters are relaxed.
     These commands will result in an INVALID_OPERATION error only if one
     of the following conditions occurs:

         * <width> is not a multiple of four or equal to TEXTURE_WIDTH.
         * <height> is not a multiple of four or equal to TEXTURE_HEIGHT.
         * <xoffset> or <yoffset> is not a multiple of four."

     Modify the paragraph added to Section 3.8.2 "Alternate Image
     Specification" at the end of the CompressedTexImage section by
     EXT_texture_compression_s3tc to say:

     "If <internalformat> is COMPRESSED_RGB_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
     COMPRESSED_RGBA_S3TC_DXT5_EXT, the compressed texture is stored using
     one of several S3TC or VTC compressed texture image formats.  The
     S3TC texture compression algorithm supports only 2D images without
     borders, while the VTC texture compression algorithm supports only
     3D images without borders.  CompressedTexImage1DARB produces an
     INVALID_ENUM error if <internalformat> is an S3TC/VTC format.
     CompressedTexImage2DARB and CompressedTexImage3DARB will produce an
     INVALID_OPERATION error if <border> is non-zero."

     Modify the paragraph added to Section 3.8.2 "Alternate Image
     Specification" at the end of the CompressedTexSubImage section by
     EXT_texture_compression_s3tc to say:

     "If the internal format of the texture image being modified is
     COMPRESSED_RGB_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT3_EXT, or COMPRESSED_RGBA_S3TC_DXT5_EXT, the
     texture is stored using one of several S3TC or VTC compressed texture
     image formats.  Since these algorithms support only 2D and 3D images,
     CompressedTexSubImage1DARB produces an INVALID_ENUM error if <format>
     is an S3TC/VTC format.  Since S3TC/VTC images are easily edited along
     4x4 and 4x4x4 texel boundaries, the limitations on
     CompressedTexSubImage2D and CompressedTexSubImage3D are relaxed.
     CompressedTexSubImage2D and CompressedTexSubImage3D will result in an
     INVALID_OPERATION error only if one of the following conditions
     occurs:

         * <width> is not a multiple of four or equal to TEXTURE_WIDTH.
         * <height> is not a multiple of four or equal to TEXTURE_HEIGHT.
         * <depth> is not a multiple of four or equal to TEXTURE_DEPTH.
         * <xoffset>, <yoffset>, or <zoffset> is not a multiple of four."

 Additions to Chapter 4 of the OpenGL 1.2.1 Specification (Per-Fragment
 Operations and the Frame Buffer)

     None.

 Additions to Chapter 5 of the OpenGL 1.2.1 Specification (Special Functions)

     None.

 Additions to Chapter 6 of the OpenGL 1.2.1 Specification (State and
 State Requests)

     None.

 Additions to Appendix A of the OpenGL 1.2.1 Specification (Invariance)

     None.

 Dependencies on ARB_texture_non_power_of_two

     There are no explicit dependencies on ARB_texture_non_power_of_two
     but the Appendix language is compatible with non-power-of-two
     texture sizes.  4x4x3 blocks are not possible if texture sizes are
     restricted to power-of-two values.

 GLX Protocol

     None.

 Errors

     The INVALID_ENUM error that was generated by CompressedTexImage3DARB
     if <internalformat> is COMPRESSED_RGB_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
     COMPRESSED_RGBA_S3TC_DXT5_EXT no longer occurs.

     INVALID_OPERATION is generated by CompressedTexImage3DARB if
     <internalformat> is COMPRESSED_RGB_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
     COMPRESSED_RGBA_S3TC_DXT5_EXT and <border> is not equal to zero.

     The INVALID_ENUM error that was generated by
     CompressedTexSubImage3DARB if <format> is
     COMPRESSED_RGB_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT3_EXT, or COMPRESSED_RGBA_S3TC_DXT5_EXT no
     longer occurs.

     INVALID_OPERATION is generated by TexSubImage3D or
     CopyTexSubImage3D if INTERNAL_FORMAT is COMPRESSED_RGB_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
     COMPRESSED_RGBA_S3TC_DXT5_EXT and any of the following apply: <width>
     is not a multiple of four or equal to TEXTURE_WIDTH; <height> is not
     a multiple of four or equal to TEXTURE_HEIGHT; <xoffset> or <yoffset>
     is not a multiple of four.

     INVALID_OPERATION is generated by CompressedTexSubImage3D
     if INTERNAL_FORMAT is COMPRESSED_RGB_S3TC_DXT1_EXT,
     COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT,
     or COMPRESSED_RGBA_S3TC_DXT5_EXT and any of the following apply:
     <width> is not a multiple of four or equal to TEXTURE_WIDTH; <height>
     is not a multiple of four or equal to TEXTURE_HEIGHT; <depth> is not
     a multiple of four or equal to TEXTURE_DEPTH; <xoffset> <yoffset>,
     or <zoffset> is not a multiple of four.

     See also errors in the GL_ARB_texture_compression and
     GL_EXT_texture_compression_s3tc specifications.

 New State

     None.

 Appendix

     VTC Compressed Texture Image Formats

     Each VTC compression format is similar to a corresponding S3TC
     compression format, but where an S3TC block encodes a 4x4 block of
     texels, a VTC block encodes a 4x4x1, 4x4x2, or 4x4x4 (or 4x4x3 if
     non-power-of-two textures are supported) block of texels.  If the
     depth of the image is four or greater, 4x4x4 blocks are used, and
     if the depth is 1 or 2, 4x4x1 or 4x4x2 blocks are used.

     (If non-power-of-two textures are supported and the depth of the
     texture is not a multiple 4, the excess texels in depth after 4x4x4
     blocks are arranged are stored with 4x4x1, 4x4x2, or 4x4x3 blocks
     as necessary to complete the texture.)

     The size in bytes of a VTC image with dimensions w, h, and d is:

         ceil(w/4) * ceil(h/4) * d * blocksize,

     where blocksize is the size of an analogous 4x4 S3TC block and is
     either 8 or 16 bytes.

     The block containing a texel at location (x,y,z) starts at an offset
     inside the image of blockIndex bytes where blockIndex is computed
     as follows:

     if (z >= 4*floor(d/4)) {
         blockIndex = blocksize * (ceil(w/4) * ceil(h/4) * 4*floor(d/4) +
                                   floor(x/4) +
                                   ceil(w/4) * (floor(y/4) +
                                                ceil(h/4) * (z-4*floor(d/4)) ));
     } else {
         blockIndex = blocksize * 4 * (floor(x/4) +
                                       ceil(w/4) * (floor(y/4) +
                                                    ceil(h/4) * floor(z/4)));
     }

     These two observations about subexpressions in the above computation
     are useful:

         4*floor(d/4) == d & ~0x3

         when z > 4*floor(d/4) and z < d, z-4*floor(d/4) == z & 0x3

     A 4x4x1 block of each of the four formats is stored in exactly the
     same way that a 4x4 block of the analogous S3TC format is stored.

     A 4x4x2, 4x4x3, or 4x4x4 block is stored as two, three, or four
     consecutive 4x4 blocks of the analogous S3TC format, one for each
     layer inside the block.  For example, a 4x4x2 DXT1 block consists of
     16 bytes in total.  The first 8 bytes encode the texels at locations
     (0,0,0) through (3,3,0), and the second 8 bytes encode the texels
     at locations (0,0,1) through (3,3,1).

     For definitions of the S3TC formats, please refer to the
     EXT_texture_compression_s3tc specification.

 Revision History

     April 20, 2004 - Relax restrictions on depth and zoffset for
     CopyTexSubImage3D and TexSubImage3D commands.  Previous restrictions
     required 1) the image level's depth to be 1 for CopyTexSubImage3D to
     work (making the command useless in practice) and 2) the depth and
     zoffset for TexSubImage3D to be a multiple 4.  If these restrictions
     were violated, an INVALID_OPERATION error was documented to be
     generated.  NVIDIA Release 60 drivers after April 20, 2004 relax
     these restrictions.  Note the restrictions on CompressedTexSubImage3D
     that depth and zoffset must be multiples of 4 still exist because the
     VTC block is a 3D 4x4x4 block (or 4x4x2 and 4x4x1 in the end cases).

     Jun 3, 2004 - Update blockIndex to support non-power-of-two dimensions
     for VTC storage.
	Name

	NV_texture_compression_vtc

	Name Strings

	GL_NV_texture_compression_vtc

	Contact

	Matt Craighead, NVIDIA Corporation (mcraighead 'at' nvidia.com)

	Notice

	Copyright NVIDIA Corporation, 2000, 2001, 2004.

	IP Status

	NVIDIA Proprietary.

	Version

	NVIDIA Date: June 3, 2004
	Version: 4

	Number

	228

	Dependencies

	Written based on the wording of the OpenGL 1.2.1 specification.

	ARB_texture_compression is required.

	EXT_texture_compression_s3tc is required.

	ARB_texture_non_power_of_two interacts with this extension.

	Overview

	This extension adds support for the VTC 3D texture compression
	formats, which are analogous to the S3TC texture compression formats,
	with the addition of some retiling in the Z direction. VTC has the
	same compression ratio as S3TC and uses 4x4x1, 4x4x2, (4x4x3 when
	non-power-of-two textures are supported), or 4x4x4 blocks.

	Issues

	* Should the enumerants' (1) values and (2) names be reused from
	the S3TC extension?

	RESOLVED: Yes and yes. There is such a close correspondence
	between the formats that introducing new values or names would
	serve no purpose.

	* Should the block alignment restrictions differ in any way from
	the block alignment restrictions in the S3TC extension?

	RESOLVED: No, except for the addition of the Z-direction block
	alignment restriction for CompressedTexSubImage3D, which is
	analogous to the X and Y restrictions.

	* Should VTC compression work with the ARB_texture_non_power_of_two
	functionality?

	RESOLVED: Yes. The blockIndex computation works for
	non-power-of-two width, height, and depth dimensions.

	Consider a 31x25x11 3D texture to be stored using VTC.
	The initial 31x25x8 portion of the volume is bricked up using
	VTC with 4x4x4 blocks where the 31x25 dimensions are rounded
	up to 32x28. Following the expanded 32x28x8 initial volume are
	the final texels arranged as 32x28x3 with 4x4x3 blocks.

	New Procedures and Functions

	None.

	New Tokens

	Accepted by the <internalformat> parameter of TexImage3D and
	CompressedTexImage3DARB and the <format> parameter of
	CompressedTexSubImage2DARB:

	COMPRESSED_RGB_S3TC_DXT1_EXT 0x83F0
	COMPRESSED_RGBA_S3TC_DXT1_EXT 0x83F1
	COMPRESSED_RGBA_S3TC_DXT3_EXT 0x83F2
	COMPRESSED_RGBA_S3TC_DXT5_EXT 0x83F3

	Additions to Chapter 2 of the OpenGL 1.2.1 Specification (OpenGL Operation)

	None.

	Additions to Chapter 3 of the OpenGL 1.2.1 Specification (Rasterization)

	Modify the paragraph added to the end of the TexSubImage discussion
	(page 123) by EXT_texture_compression_s3tc to say:

	"If the internal format of the texture image being modified is
	COMPRESSED_RGB_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT3_EXT, or COMPRESSED_RGBA_S3TC_DXT5_EXT, the
	texture is stored using one of several S3TC or VTC compressed texture
	image formats. Such images are easily edited along 4x4 texel
	boundaries, so the limitations on TexSubImage2D, TexSubImage3D,
	CopyTexSubImage2D, and CopyTexSubImage3D parameters are relaxed.
	These commands will result in an INVALID_OPERATION error only if one
	of the following conditions occurs:

	* <width> is not a multiple of four or equal to TEXTURE_WIDTH.
	* <height> is not a multiple of four or equal to TEXTURE_HEIGHT.
	* <xoffset> or <yoffset> is not a multiple of four."

	Modify the paragraph added to Section 3.8.2 "Alternate Image
	Specification" at the end of the CompressedTexImage section by
	EXT_texture_compression_s3tc to say:

	"If <internalformat> is COMPRESSED_RGB_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
	COMPRESSED_RGBA_S3TC_DXT5_EXT, the compressed texture is stored using
	one of several S3TC or VTC compressed texture image formats. The
	S3TC texture compression algorithm supports only 2D images without
	borders, while the VTC texture compression algorithm supports only
	3D images without borders. CompressedTexImage1DARB produces an
	INVALID_ENUM error if <internalformat> is an S3TC/VTC format.
	CompressedTexImage2DARB and CompressedTexImage3DARB will produce an
	INVALID_OPERATION error if <border> is non-zero."

	Modify the paragraph added to Section 3.8.2 "Alternate Image
	Specification" at the end of the CompressedTexSubImage section by
	EXT_texture_compression_s3tc to say:

	"If the internal format of the texture image being modified is
	COMPRESSED_RGB_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT3_EXT, or COMPRESSED_RGBA_S3TC_DXT5_EXT, the
	texture is stored using one of several S3TC or VTC compressed texture
	image formats. Since these algorithms support only 2D and 3D images,
	CompressedTexSubImage1DARB produces an INVALID_ENUM error if <format>
	is an S3TC/VTC format. Since S3TC/VTC images are easily edited along
	4x4 and 4x4x4 texel boundaries, the limitations on
	CompressedTexSubImage2D and CompressedTexSubImage3D are relaxed.
	CompressedTexSubImage2D and CompressedTexSubImage3D will result in an
	INVALID_OPERATION error only if one of the following conditions
	occurs:

	* <width> is not a multiple of four or equal to TEXTURE_WIDTH.
	* <height> is not a multiple of four or equal to TEXTURE_HEIGHT.
	* <depth> is not a multiple of four or equal to TEXTURE_DEPTH.
	* <xoffset>, <yoffset>, or <zoffset> is not a multiple of four."

	Additions to Chapter 4 of the OpenGL 1.2.1 Specification (Per-Fragment
	Operations and the Frame Buffer)

	None.

	Additions to Chapter 5 of the OpenGL 1.2.1 Specification (Special Functions)

	None.

	Additions to Chapter 6 of the OpenGL 1.2.1 Specification (State and
	State Requests)

	None.

	Additions to Appendix A of the OpenGL 1.2.1 Specification (Invariance)

	None.

	Dependencies on ARB_texture_non_power_of_two

	There are no explicit dependencies on ARB_texture_non_power_of_two
	but the Appendix language is compatible with non-power-of-two
	texture sizes. 4x4x3 blocks are not possible if texture sizes are
	restricted to power-of-two values.

	GLX Protocol

	None.

	Errors

	The INVALID_ENUM error that was generated by CompressedTexImage3DARB
	if <internalformat> is COMPRESSED_RGB_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
	COMPRESSED_RGBA_S3TC_DXT5_EXT no longer occurs.

	INVALID_OPERATION is generated by CompressedTexImage3DARB if
	<internalformat> is COMPRESSED_RGB_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
	COMPRESSED_RGBA_S3TC_DXT5_EXT and <border> is not equal to zero.

	The INVALID_ENUM error that was generated by
	CompressedTexSubImage3DARB if <format> is
	COMPRESSED_RGB_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT3_EXT, or COMPRESSED_RGBA_S3TC_DXT5_EXT no
	longer occurs.

	INVALID_OPERATION is generated by TexSubImage3D or
	CopyTexSubImage3D if INTERNAL_FORMAT is COMPRESSED_RGB_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT, or
	COMPRESSED_RGBA_S3TC_DXT5_EXT and any of the following apply: <width>
	is not a multiple of four or equal to TEXTURE_WIDTH; <height> is not
	a multiple of four or equal to TEXTURE_HEIGHT; <xoffset> or <yoffset>
	is not a multiple of four.

	INVALID_OPERATION is generated by CompressedTexSubImage3D
	if INTERNAL_FORMAT is COMPRESSED_RGB_S3TC_DXT1_EXT,
	COMPRESSED_RGBA_S3TC_DXT1_EXT, COMPRESSED_RGBA_S3TC_DXT3_EXT,
	or COMPRESSED_RGBA_S3TC_DXT5_EXT and any of the following apply:
	<width> is not a multiple of four or equal to TEXTURE_WIDTH; <height>
	is not a multiple of four or equal to TEXTURE_HEIGHT; <depth> is not
	a multiple of four or equal to TEXTURE_DEPTH; <xoffset> <yoffset>,
	or <zoffset> is not a multiple of four.

	See also errors in the GL_ARB_texture_compression and
	GL_EXT_texture_compression_s3tc specifications.

	New State

	None.

	Appendix

	VTC Compressed Texture Image Formats

	Each VTC compression format is similar to a corresponding S3TC
	compression format, but where an S3TC block encodes a 4x4 block of
	texels, a VTC block encodes a 4x4x1, 4x4x2, or 4x4x4 (or 4x4x3 if
	non-power-of-two textures are supported) block of texels. If the
	depth of the image is four or greater, 4x4x4 blocks are used, and
	if the depth is 1 or 2, 4x4x1 or 4x4x2 blocks are used.

	(If non-power-of-two textures are supported and the depth of the
	texture is not a multiple 4, the excess texels in depth after 4x4x4
	blocks are arranged are stored with 4x4x1, 4x4x2, or 4x4x3 blocks
	as necessary to complete the texture.)

	The size in bytes of a VTC image with dimensions w, h, and d is:

	ceil(w/4) * ceil(h/4) * d * blocksize,

	where blocksize is the size of an analogous 4x4 S3TC block and is
	either 8 or 16 bytes.

	The block containing a texel at location (x,y,z) starts at an offset
	inside the image of blockIndex bytes where blockIndex is computed
	as follows:

	if (z >= 4*floor(d/4)) {
	blockIndex = blocksize * (ceil(w/4) * ceil(h/4) * 4*floor(d/4) +
	floor(x/4) +
	ceil(w/4) * (floor(y/4) +
	ceil(h/4) * (z-4*floor(d/4)) ));
	} else {
	blockIndex = blocksize * 4 * (floor(x/4) +
	ceil(w/4) * (floor(y/4) +
	ceil(h/4) * floor(z/4)));
	}

	These two observations about subexpressions in the above computation
	are useful:

	4*floor(d/4) == d & ~0x3

	when z > 4floor(d/4) and z < d, z-4floor(d/4) == z & 0x3

	A 4x4x1 block of each of the four formats is stored in exactly the
	same way that a 4x4 block of the analogous S3TC format is stored.

	A 4x4x2, 4x4x3, or 4x4x4 block is stored as two, three, or four
	consecutive 4x4 blocks of the analogous S3TC format, one for each
	layer inside the block. For example, a 4x4x2 DXT1 block consists of
	16 bytes in total. The first 8 bytes encode the texels at locations
	(0,0,0) through (3,3,0), and the second 8 bytes encode the texels
	at locations (0,0,1) through (3,3,1).

	For definitions of the S3TC formats, please refer to the
	EXT_texture_compression_s3tc specification.

	Revision History

	April 20, 2004 - Relax restrictions on depth and zoffset for
	CopyTexSubImage3D and TexSubImage3D commands. Previous restrictions
	required 1) the image level's depth to be 1 for CopyTexSubImage3D to
	work (making the command useless in practice) and 2) the depth and
	zoffset for TexSubImage3D to be a multiple 4. If these restrictions
	were violated, an INVALID_OPERATION error was documented to be
	generated. NVIDIA Release 60 drivers after April 20, 2004 relax
	these restrictions. Note the restrictions on CompressedTexSubImage3D
	that depth and zoffset must be multiples of 4 still exist because the
	VTC block is a 3D 4x4x4 block (or 4x4x2 and 4x4x1 in the end cases).

	Jun 3, 2004 - Update blockIndex to support non-power-of-two dimensions
	for VTC storage.