Name ARB_texture_compression_bptc Name Strings GL_ARB_texture_compression_bptc Contact Eric Werness, NVIDIA Corporation (ewerness 'at' nvidia.com) Piers Daniell, NVIDIA Corporation (pdaniell 'at' nvidia.com) Contributors Barthold Lichtenbelt, NVIDIA Bill Licea-Kane, AMD Graham Sellers, AMD Greg Roth, NVIDIA Jeannot Breton, NVIDIA Jeff Bolz, NVIDIA Nick Haemel, AMD Pat Brown, NVIDIA Pierre Boudier, AMD Piers Daniell, NVIDIA Notice Copyright (c) 2010-2013 The Khronos Group Inc. Copyright terms at http://www.khronos.org/registry/speccopyright.html Specification Update Policy Khronos-approved extension specifications are updated in response to issues and bugs prioritized by the Khronos OpenGL Working Group. For extensions which have been promoted to a core Specification, fixes will first appear in the latest version of that core Specification, and will eventually be backported to the extension document. This policy is described in more detail at https://www.khronos.org/registry/OpenGL/docs/update_policy.php Status Complete. Approved by the ARB at the 2010/01/22 F2F meeting. Approved by the Khronos Board of Promoters on March 10, 2010. Version Last Modified Date: October 30, 2019 Revision: 9 Number ARB Extension #77 Dependencies OpenGL 1.3 or ARB_texture_compression is required. This extension is written against the OpenGL 3.2 Specification (Compatibility Profile). Overview This extension provides additional texture compression functionality specific to the BPTC and BPTC_FLOAT compressed texture formats (called BC7 and BC6H respectively in Microsoft's DirectX API), subject to all the requirements and limitations described by the extension GL_ARB_texture_compression. Traditional block compression methods as typified by s3tc and latc compress a block of pixels into indicies along a gradient. This works well for smooth images, but can have quality issues along sharp edges and strong chrominance transitions. To improve quality in these problematic cases, the BPTC formats can divide each block into multiple partitions, each of which are compressed using an independent gradient. In addition, it is desirable to directly support high dynamic range imagery in compressed formats, which is accomplished by the BPTC_FLOAT formats. IP Status No known IP claims. New Procedures and Functions None. New Tokens Accepted by the parameter of TexImage2D, TexImage3D, CopyTexImage2D, CopyTexImage3D, CompressedTexImage2DARB, and CompressedTexImage3DARB and the parameter of CompressedTexSubImage2DARB and CompressedTexSubImage3DARB: COMPRESSED_RGBA_BPTC_UNORM_ARB 0x8E8C COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB 0x8E8D COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB 0x8E8E COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB 0x8E8F Additions to Chapter 2 of the OpenGL 3.2 Specification (OpenGL Operation) None. Additions to Chapter 3 of the OpenGL 3.2 Specification (Rasterization) Add to Table 3.20: Generic and specific compressed internal formats Compressed Internal Format Base Internal Format Type ========================== ==================== ======== COMPRESSED_RGBA_BPTC_UNORM_ARB RGBA Specific COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB RGBA Specific COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB RGB Specific COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB RGB Specific Modify Section 3.9.2, Alternate Texture Image Specification Commands (add to end of TexSubImage discussion, p.231 -- after edit from the ARB_texture_compression spec) If the internal format of the texture image being modified is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB the texture is stored using the specified BPTC compressed texture image format. Such images are easily edited along 4x4 texel boundaries, so the limitations on TexSubImage2D, TexSubImage3D, CopyTexSubImage2D, and CopyTexSubImage3D parameters are relaxed. TexSubImage2D, TexSubImage3D, CopyTexSubImage2D, and CopyTexSubImage3D will result in an INVALID_OPERATION error only if one of the following conditions occurs: * is not a multiple of four, plus is not equal to TEXTURE_WIDTH, and either or is non-zero; * is not a multiple of four, plus is not equal to TEXTURE_HEIGHT, and either or is non-zero; or * or is not a multiple of four. The contents of any 4x4 block of texels of a BPTC compressed texture image that does not intersect the area being modified are preserved during valid TexSubImage2D, TexSubImage3D, CopyTexSubImage2D, and CopyTexSubImage3D calls. Add to Section 3.9.3, Compressed Texture Images (adding to the end of the CompressedTexImage section introduced by the ARB_texture_compression spec) If is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB the compressed texture is stored using the specified BPTC compressed texture image format. The BPTC texture compression algorithm supports only 2D images without borders, though 3D images can be compressed as multiple slices of compressed 2D images. CompressedTexImage1DARB produces an INVALID_ENUM error if is a BPTC format. CompressedTexImage2DARB and CompressedTexImage3DARB will produce an INVALID_OPERATION error if is non-zero. Add to Section 3.9.3, Compressed Texture Images (adding to the end of the CompressedTexSubImage section introduced by the ARB_texture_compression spec) If the internal format of the texture image being modified is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB the texture is stored using the specified BPTC compressed texture image formats. Since the BPTC texture compression algorithm supports only 2D images, CompressedTexSubImage1DARB produces an INVALID_ENUM error if is a BPTC format. Since BPTC images are easily edited along 4x4 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: * is not a multiple of four, and plus is not equal to TEXTURE_WIDTH; * is not a multiple of four, and plus is not equal to TEXTURE_HEIGHT; or * or is not a multiple of four. The contents of any 4x4 block of texels of a BPTC compressed texture image that does not intersect the area being modified are preserved during valid TexSubImage2D/3D and CopyTexSubImage2D/3D calls. Additions to Chapter 4 of the OpenGL 3.2 Specification (Per-Fragment Operations and the Frame Buffer) None. Additions to Chapter 5 of the OpenGL 3.2 Specification (Special Functions) None. Additions to Chapter 6 of the OpenGL 3.2 Specification (State and State Requests) None. Additions to Appendix A of the OpenGL 3.2 Specification (Invariance) None. Additions to the AGL/GLX/WGL Specifications None. GLX Protocol None. Errors INVALID_ENUM is generated by CompressedTexImage1DARB if is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB. INVALID_OPERATION is generated by CompressedTexImage2DARB if is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB and is not equal to zero. INVALID_ENUM is generated by CompressedTexSubImage1DARB if is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB. INVALID_OPERATION is generated by TexSubImage2D or CopyTexSubImage2D if TEXTURE_INTERNAL_FORMAT is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB and any of the following apply: * is not a multiple of four, plus is not equal to TEXTURE_WIDTH, and either or is non-zero; * is not a multiple of four, plus is not equal to TEXTURE_HEIGHT, and either or is non-zero; or * or is not a multiple of four. INVALID_OPERATION is generated by CompressedTexSubImage2D if TEXTURE_INTERNAL_FORMAT is COMPRESSED_RGBA_BPTC_UNORM_ARB, COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB, or COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB and any of the following apply: * is not a multiple of four, and plus is not equal to TEXTURE_WIDTH; * is not a multiple of four, and plus is not equal to TEXTURE_HEIGHT; or * or is not a multiple of four. The following restrictions from the ARB_texture_compression specification do not apply to BPTC texture formats, since subimage modification is straightforward as long as the subimage is properly aligned. DELETE: INVALID_OPERATION is generated by TexSubImage1D, TexSubImage2D, DELETE: TexSubImage3D, CopyTexSubImage1D, CopyTexSubImage2D, or DELETE: CopyTexSubImage3D if the internal format of the texture image is DELETE: compressed and , , or does not equal DELETE: -b, where b is value of TEXTURE_BORDER. DELETE: INVALID_VALUE is generated by CompressedTexSubImage1DARB, DELETE: CompressedTexSubImage2DARB, or CompressedTexSubImage3DARB if the DELETE: entire texture image is not being edited: if , DELETE: , or is greater than -b, + is DELETE: less than w+b, + is less than h+b, or DELETE: + is less than d+b, where b is the value of DELETE: TEXTURE_BORDER, w is the value of TEXTURE_WIDTH, h is the value of DELETE: TEXTURE_HEIGHT, and d is the value of TEXTURE_DEPTH. See also errors in the GL_ARB_texture_compression specification. New State In the "Textures" state table, increment the TEXTURE_INTERNAL_FORMAT subscript for Z by 4 in the "Type" row. New Implementation Dependent State None Appendix BPTC Compressed Texture Image Format Compressed texture images stored using the BPTC compressed image formats are represented as a collection of 4x4 texel blocks, where each block contains 128 bits of texel data. The image is encoded as a normal 2D raster image in which each 4x4 block is treated as a single pixel. If a BPTC image has a width or height that is not a multiple of four, the data corresponding to texels outside the image are irrelevant and undefined. When a BPTC image with a width of , height of , and block size of (16 bytes) is decoded, the corresponding image size (in bytes) is: ceil(/4) * ceil(/4) * blocksize. When decoding a BPTC image, the block containing the texel at offset (, ) begins at an offset (in bytes) relative to the base of the image of: blocksize * (ceil(/4) * floor(/4) + floor(/4)). The data corresponding to a specific texel (, ) are extracted from a 4x4 texel block using a relative (x,y) value of ( modulo 4, modulo 4). There are two distinct BPTC image formats each of which has two variants. COMPRESSED_RGBA_BPTC_UNORM_ARB and COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB compress 8-bit fixed-point data. COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB and COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB compress high dynamic range floating point values. The formats are similar, so the description of the float format will reference significant sections of the UNORM description. COMPRESSED_RGBA_BPTC_UNORM_ARB (and the SRGB_ALPHA equivalent): Each 4x4 block of texels consists of 128 bits of RGBA or SRGB_ALPHA image data. Each block contains enough information to select and decode a pair of colors called endpoints, interpolate between those endpoints in a variety of ways, then remap the result into the final output. Each block can contain data in one of eight modes. The mode is identified by the lowest bits of the lowest byte. It is encoded as zero or more zeros followed by a one. For example, using x to indicate a bit not included in the mode number, mode 0 is encoded as xxxxxxx1 in the low byte in binary, mode 5 is xx100000, and mode 7 is 10000000. Encoding the low byte as zero is reserved and should not be used when encoding a BPTC texture. All further decoding is driven by the values derived from the mode listed in Table.M below. The fields in the block are always in the same order for all modes. Starting at the lowest bit after the mode and going up from LSB to MSB in byte stream order, these fields are: partition number, rotation, index selection, color, alpha, per-endpoint P-bit, shared P-bit, primary indices, and secondary indices. The number of bits to be read in each field is determined directly from the table. Each block can be divided into between 1 and 3 groups of pixels with independent compression parameters called subsets. A texel in a block with one subset is always considered to be in subset zero. Otherwise, a number determined by the number of partition bits is used to look up in the partition tables Table.P2 or Table.P3 for 2 and 3 subsets respectively. This partitioning is indexed by the X and Y within the block to generate the subset index. Each block has two colors for each subset, stored first by endpoint, then by subset, then by color. For example, a format with two subsets and five color bits would have five bits of red for endpoint 0 of the first subset, then five bits of red for endpoint 1, then the two ends of the second subset, then green and blue stored similarly. If a block has non-zero alpha bits, the alpha data follows the color data with the same organization. If not, alpha is overridden to 1.0. These bits are treated as the high bits of a fixed-point value in a byte. If the format has shared P-bits, there are two endpoint bits, the lower of which applies to both endpoints of subset 0 and the upper of which applies to both endpoints of subset 1. If the format has a per-endpoint P-bits, then there are 2*subsets P-bits stored in the same order as color and alpha. Both kinds of P-bits are added as a bit below the color data stored in the byte. So, for a format with 5 red bits, the P-bit ends up in bit 2. For final scaling, the top bits of the value are replicated into any remaining bits in the byte. For the preceding example, bits 6 and 7 would be written to bits 0 and 1. The endpoint colors are interpolated using index values stored in the block. The index bits are stored in x-major order. Each index has the number of bits indicated by the mode except for one special index per subset called the anchor index. Since the ordering of the endpoints is unimportant, we can save one bit on one index per subset by ordering the endpoints such that the highest bit is guaranteed to be zero. In partition zero, the anchor index is always index zero. In other partitions, the anchor index is specified by tables Table.A2 and Table.A3. If secondary index bits are present, they are read in the same manner. The anchor index information is only used to determine the number of bits each index has when it's read from the block data. The endpoint color and alpha values used for final interpolation are the decoded values corresponding to the applicable subset as selected above. The index value for interpolating color comes from the secondary index for the texel if the format has an index selection bit and its value is one and from the primary index otherwise. The alpha index comes from the secondary index if the block has a secondary index and the block either doesn't have an index selection bit or that bit is zero and the primary index otherwise. Interpolation is always performed using a 6-bit interpolation factor. The effective interpolation factors for 2, 3, and 4 bit indices are given below: 2: 0, 21, 43, 64 3: 0, 9, 18, 27, 37, 46, 55, 64 4: 0, 4, 9, 13, 17, 21, 26, 30, 34, 38, 43, 47, 51, 55, 60, 64 The interpolation results in an RGBA color. If rotation bits are present, this color is remapped according to: 0: no change 1: swap(a,r) 2: swap(a,g) 3: swap(a,b) These 8-bit values show up in the shader interpreted as either RGBA8 or SRGB8_ALPHA8 for COMPRESSED_RGBA_BPTC_UNORM_ARB and COMPRESSED_SRGB_ALPHA_BPTC_UNORM_ARB respectively. Table.M Mode NS PB RB ISB CB AB EPB SPB IB IB2 ---- -- -- -- --- -- -- --- --- -- --- 0 3 4 0 0 4 0 1 0 3 0 1 2 6 0 0 6 0 0 1 3 0 2 3 6 0 0 5 0 0 0 2 0 3 2 6 0 0 7 0 1 0 2 0 4 1 0 2 1 5 6 0 0 2 3 5 1 0 2 0 7 8 0 0 2 2 6 1 0 0 0 7 7 1 0 4 0 7 2 6 0 0 5 5 1 0 2 0 The columns are as as follows: Mode: As described above NS: Number of subsets in each partition PB: Partition bits RB: Rotation bits ISB: Index selection bits CB: Color bits AB: Alpha bits EPB: Endpoint P-bits SPB: Shared P-bits IB: Index bits per element IB2: Secondary index bits per element Table.P2 (each row is one 4x4 block) 0,0,1,1,0,0,1,1,0,0,1,1,0,0,1,1 0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1 0,1,1,1,0,1,1,1,0,1,1,1,0,1,1,1 0,0,0,1,0,0,1,1,0,0,1,1,0,1,1,1 0,0,0,0,0,0,0,1,0,0,0,1,0,0,1,1 0,0,1,1,0,1,1,1,0,1,1,1,1,1,1,1 0,0,0,1,0,0,1,1,0,1,1,1,1,1,1,1 0,0,0,0,0,0,0,1,0,0,1,1,0,1,1,1 0,0,0,0,0,0,0,0,0,0,0,1,0,0,1,1 0,0,1,1,0,1,1,1,1,1,1,1,1,1,1,1 0,0,0,0,0,0,0,1,0,1,1,1,1,1,1,1 0,0,0,0,0,0,0,0,0,0,0,1,0,1,1,1 0,0,0,1,0,1,1,1,1,1,1,1,1,1,1,1 0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1 0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1 0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1 0,0,0,0,1,0,0,0,1,1,1,0,1,1,1,1 0,1,1,1,0,0,0,1,0,0,0,0,0,0,0,0 0,0,0,0,0,0,0,0,1,0,0,0,1,1,1,0 0,1,1,1,0,0,1,1,0,0,0,1,0,0,0,0 0,0,1,1,0,0,0,1,0,0,0,0,0,0,0,0 0,0,0,0,1,0,0,0,1,1,0,0,1,1,1,0 0,0,0,0,0,0,0,0,1,0,0,0,1,1,0,0 0,1,1,1,0,0,1,1,0,0,1,1,0,0,0,1 0,0,1,1,0,0,0,1,0,0,0,1,0,0,0,0 0,0,0,0,1,0,0,0,1,0,0,0,1,1,0,0 0,1,1,0,0,1,1,0,0,1,1,0,0,1,1,0 0,0,1,1,0,1,1,0,0,1,1,0,1,1,0,0 0,0,0,1,0,1,1,1,1,1,1,0,1,0,0,0 0,0,0,0,1,1,1,1,1,1,1,1,0,0,0,0 0,1,1,1,0,0,0,1,1,0,0,0,1,1,1,0 0,0,1,1,1,0,0,1,1,0,0,1,1,1,0,0 0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1 0,0,0,0,1,1,1,1,0,0,0,0,1,1,1,1 0,1,0,1,1,0,1,0,0,1,0,1,1,0,1,0 0,0,1,1,0,0,1,1,1,1,0,0,1,1,0,0 0,0,1,1,1,1,0,0,0,0,1,1,1,1,0,0 0,1,0,1,0,1,0,1,1,0,1,0,1,0,1,0 0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1 0,1,0,1,1,0,1,0,1,0,1,0,0,1,0,1 0,1,1,1,0,0,1,1,1,1,0,0,1,1,1,0 0,0,0,1,0,0,1,1,1,1,0,0,1,0,0,0 0,0,1,1,0,0,1,0,0,1,0,0,1,1,0,0 0,0,1,1,1,0,1,1,1,1,0,1,1,1,0,0 0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0 0,0,1,1,1,1,0,0,1,1,0,0,0,0,1,1 0,1,1,0,0,1,1,0,1,0,0,1,1,0,0,1 0,0,0,0,0,1,1,0,0,1,1,0,0,0,0,0 0,1,0,0,1,1,1,0,0,1,0,0,0,0,0,0 0,0,1,0,0,1,1,1,0,0,1,0,0,0,0,0 0,0,0,0,0,0,1,0,0,1,1,1,0,0,1,0 0,0,0,0,0,1,0,0,1,1,1,0,0,1,0,0 0,1,1,0,1,1,0,0,1,0,0,1,0,0,1,1 0,0,1,1,0,1,1,0,1,1,0,0,1,0,0,1 0,1,1,0,0,0,1,1,1,0,0,1,1,1,0,0 0,0,1,1,1,0,0,1,1,1,0,0,0,1,1,0 0,1,1,0,1,1,0,0,1,1,0,0,1,0,0,1 0,1,1,0,0,0,1,1,0,0,1,1,1,0,0,1 0,1,1,1,1,1,1,0,1,0,0,0,0,0,0,1 0,0,0,1,1,0,0,0,1,1,1,0,0,1,1,1 0,0,0,0,1,1,1,1,0,0,1,1,0,0,1,1 0,0,1,1,0,0,1,1,1,1,1,1,0,0,0,0 0,0,1,0,0,0,1,0,1,1,1,0,1,1,1,0 0,1,0,0,0,1,0,0,0,1,1,1,0,1,1,1 Table.P3 0,0,1,1,0,0,1,1,0,2,2,1,2,2,2,2 0,0,0,1,0,0,1,1,2,2,1,1,2,2,2,1 0,0,0,0,2,0,0,1,2,2,1,1,2,2,1,1 0,2,2,2,0,0,2,2,0,0,1,1,0,1,1,1 0,0,0,0,0,0,0,0,1,1,2,2,1,1,2,2 0,0,1,1,0,0,1,1,0,0,2,2,0,0,2,2 0,0,2,2,0,0,2,2,1,1,1,1,1,1,1,1 0,0,1,1,0,0,1,1,2,2,1,1,2,2,1,1 0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2 0,0,0,0,1,1,1,1,1,1,1,1,2,2,2,2 0,0,0,0,1,1,1,1,2,2,2,2,2,2,2,2 0,0,1,2,0,0,1,2,0,0,1,2,0,0,1,2 0,1,1,2,0,1,1,2,0,1,1,2,0,1,1,2 0,1,2,2,0,1,2,2,0,1,2,2,0,1,2,2 0,0,1,1,0,1,1,2,1,1,2,2,1,2,2,2 0,0,1,1,2,0,0,1,2,2,0,0,2,2,2,0 0,0,0,1,0,0,1,1,0,1,1,2,1,1,2,2 0,1,1,1,0,0,1,1,2,0,0,1,2,2,0,0 0,0,0,0,1,1,2,2,1,1,2,2,1,1,2,2 0,0,2,2,0,0,2,2,0,0,2,2,1,1,1,1 0,1,1,1,0,1,1,1,0,2,2,2,0,2,2,2 0,0,0,1,0,0,0,1,2,2,2,1,2,2,2,1 0,0,0,0,0,0,1,1,0,1,2,2,0,1,2,2 0,0,0,0,1,1,0,0,2,2,1,0,2,2,1,0 0,1,2,2,0,1,2,2,0,0,1,1,0,0,0,0 0,0,1,2,0,0,1,2,1,1,2,2,2,2,2,2 0,1,1,0,1,2,2,1,1,2,2,1,0,1,1,0 0,0,0,0,0,1,1,0,1,2,2,1,1,2,2,1 0,0,2,2,1,1,0,2,1,1,0,2,0,0,2,2 0,1,1,0,0,1,1,0,2,0,0,2,2,2,2,2 0,0,1,1,0,1,2,2,0,1,2,2,0,0,1,1 0,0,0,0,2,0,0,0,2,2,1,1,2,2,2,1 0,0,0,0,0,0,0,2,1,1,2,2,1,2,2,2 0,2,2,2,0,0,2,2,0,0,1,2,0,0,1,1 0,0,1,1,0,0,1,2,0,0,2,2,0,2,2,2 0,1,2,0,0,1,2,0,0,1,2,0,0,1,2,0 0,0,0,0,1,1,1,1,2,2,2,2,0,0,0,0 0,1,2,0,1,2,0,1,2,0,1,2,0,1,2,0 0,1,2,0,2,0,1,2,1,2,0,1,0,1,2,0 0,0,1,1,2,2,0,0,1,1,2,2,0,0,1,1 0,0,1,1,1,1,2,2,2,2,0,0,0,0,1,1 0,1,0,1,0,1,0,1,2,2,2,2,2,2,2,2 0,0,0,0,0,0,0,0,2,1,2,1,2,1,2,1 0,0,2,2,1,1,2,2,0,0,2,2,1,1,2,2 0,0,2,2,0,0,1,1,0,0,2,2,0,0,1,1 0,2,2,0,1,2,2,1,0,2,2,0,1,2,2,1 0,1,0,1,2,2,2,2,2,2,2,2,0,1,0,1 0,0,0,0,2,1,2,1,2,1,2,1,2,1,2,1 0,1,0,1,0,1,0,1,0,1,0,1,2,2,2,2 0,2,2,2,0,1,1,1,0,2,2,2,0,1,1,1 0,0,0,2,1,1,1,2,0,0,0,2,1,1,1,2 0,0,0,0,2,1,1,2,2,1,1,2,2,1,1,2 0,2,2,2,0,1,1,1,0,1,1,1,0,2,2,2 0,0,0,2,1,1,1,2,1,1,1,2,0,0,0,2 0,1,1,0,0,1,1,0,0,1,1,0,2,2,2,2 0,0,0,0,0,0,0,0,2,1,1,2,2,1,1,2 0,1,1,0,0,1,1,0,2,2,2,2,2,2,2,2 0,0,2,2,0,0,1,1,0,0,1,1,0,0,2,2 0,0,2,2,1,1,2,2,1,1,2,2,0,0,2,2 0,0,0,0,0,0,0,0,0,0,0,0,2,1,1,2 0,0,0,2,0,0,0,1,0,0,0,2,0,0,0,1 0,2,2,2,1,2,2,2,0,2,2,2,1,2,2,2 0,1,0,1,2,2,2,2,2,2,2,2,2,2,2,2 0,1,1,1,2,0,1,1,2,2,0,1,2,2,2,0 Table.A2 (Anchor index values for the second subset of two-subset partitioning) (wrapped for readability - values run right then down) 15,15,15,15,15,15,15,15, 15,15,15,15,15,15,15,15, 15, 2, 8, 2, 2, 8, 8,15, 2, 8, 2, 2, 8, 8, 2, 2, 15,15, 6, 8, 2, 8,15,15, 2, 8, 2, 2, 2,15,15, 6, 6, 2, 6, 8,15,15, 2, 2, 15,15,15,15,15, 2, 2,15, Table.A3a (Anchor index values for the second subset of three-subset partitioning) (wrapped for readability - values run right then down) 3, 3,15,15, 8, 3,15,15, 8, 8, 6, 6, 6, 5, 3, 3, 3, 3, 8,15, 3, 3, 6,10, 5, 8, 8, 6, 8, 5,15,15, 8,15, 3, 5, 6,10, 8,15, 15, 3,15, 5,15,15,15,15, 3,15, 5, 5, 5, 8, 5,10, 5,10, 8,13,15,12, 3, 3, Table.A3b (Anchor index values for the third subset of three-subset partitioning) (wrapped for readability - values run right then down) 15, 8, 8, 3,15,15, 3, 8, 15,15,15,15,15,15,15, 8, 15, 8,15, 3,15, 8,15, 8, 3,15, 6,10,15,15,10, 8, 15, 3,15,10,10, 8, 9,10, 6,15, 8,15, 3, 6, 6, 8, 15, 3,15,15,15,15,15,15, 15,15,15,15, 3,15,15, 8, COMPRESSED_RGB_BPTC_SIGNED_FLOAT_ARB and COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB: Each 4x4 block of texels consists of 128 bits of RGB data. These formats are very similar and will be described together. In the description and pseudocode below, will be used as a condition which is true for the SIGNED format and false for the UNSIGNED format. Both formats only contain RGB data, so the returned alpha value is 1.0. If a block uses a reserved or invalid encoding, the return value is (0,0,0,1). Each block can contain data in one of 14 modes. The mode number is encoded in either the low two bits or the low five bits. If the low two bits are less than two, that is the mode number, otherwise the low five bits the mode number. Mode numbers not listed in Table.MF are reserved (19, 23, 27, and 31). The data for the compressed blocks is stored in a different format for each mode. The formats are specified in Table.F. The format strings are intended to be read from left to right with the LSB on the left. Each element is of the form v[a:b]. If a>=b, this indicates to extract b-a+1 bits from the block at that location and put it in the corresponding bits of the variable v. If a= 15) unq = x; else if (x == 0) unq = 0; else if (x == ((1<> (EPB-1); The signed float unquantization is similar, but needs to worry about orienting the negative range: s = 0; if (EPB >= 16) unq = x; else { if (x < 0) { s = 1; x = -x; } if (x == 0) unq = 0; else if (x >= ((1<<(EPB-1))-1)) unq = 0x7FFF; else unq = ((x << 15) + 0x4000) >> (EPB-1); if (s) unq = -unq; } After the endpoints are unquantized, interpolation proceeds as in the fixed-point formats above including the interpolation weight table. The interpolated values are passed through a final unquantization step. For the unsigned format, this step simply multiplies by 31/64. The signed format negates negative components, multiplies by 31/32, then or's in the sign bit if the original value was negative. The resultant value should be a legal 16-bit half float which is then returned as a float to the shader. Table.MF MN Tr PB EPB Delta Bits -- -- -- --- ---------- 0 1 5 10 {5, 5, 5} 1 1 5 7 {6, 6, 6} 2 1 5 11 {5, 4, 4} 6 1 5 11 {4, 5, 4} 10 1 5 11 {4, 4, 5} 14 1 5 9 {5, 5, 5} 18 1 5 8 {6, 5, 5} 22 1 5 8 {5, 6, 5} 26 1 5 8 {5, 5, 6} 30 0 5 6 {6, 6, 6} 3 0 0 10 {10, 10, 10} 7 1 0 11 {9, 9, 9} 11 1 0 12 {8, 8, 8} 15 1 0 16 {4, 4, 4} MN: Mode number Tr: Transformed endpoints PB: Partition bits EPB: Endpoint bits Table.F MN Format -- ------------------------------------------------------------------------ 0 m[1:0],g2[4],b2[4],b3[4],r0[9:0],g0[9:0],b0[9:0],r1[4:0],g3[4],g2[3:0], g1[4:0],b3[0],g3[3:0],b1[4:0],b3[1],b2[3:0],r2[4:0],b3[2],r3[4:0],b3[3] 1 m[1:0],g2[5],g3[4],g3[5],r0[6:0],b3[0],b3[1],b2[4],g0[6:0],b2[5],b3[2], g2[4],b0[6:0],b3[3],b3[5],b3[4],r1[5:0],g2[3:0],g1[5:0],g3[3:0],b1[5:0], b2[3:0],r2[5:0],r3[5:0] 2 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[4:0],r0[10],g2[3:0],g1[3:0],g0[10], b3[0],g3[3:0],b1[3:0],b0[10],b3[1],b2[3:0],r2[4:0],b3[2],r3[4:0],b3[3] 6 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[3:0],r0[10],g3[4],g2[3:0],g1[4:0], g0[10],g3[3:0],b1[3:0],b0[10],b3[1],b2[3:0],r2[3:0],b3[0],b3[2],r3[3:0], g2[4],b3[3] 10 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[3:0],r0[10],b2[4],g2[3:0],g1[3:0], g0[10],b3[0],g3[3:0],b1[4:0],b0[10],b2[3:0],r2[3:0],b3[1],b3[2],r3[3:0], b3[4],b3[3] 14 m[4:0],r0[8:0],b2[4],g0[8:0],g2[4],b0[8:0],b3[4],r1[4:0],g3[4],g2[3:0], g1[4:0],b3[0],g3[3:0],b1[4:0],b3[1],b2[3:0],r2[4:0],b3[2],r3[4:0],b3[3] 18 m[4:0],r0[7:0],g3[4],b2[4],g0[7:0],b3[2],g2[4],b0[7:0],b3[3],b3[4], r1[5:0],g2[3:0],g1[4:0],b3[0],g3[3:0],b1[4:0],b3[1],b2[3:0],r2[5:0], r3[5:0] 22 m[4:0],r0[7:0],b3[0],b2[4],g0[7:0],g2[5],g2[4],b0[7:0],g3[5],b3[4], r1[4:0],g3[4],g2[3:0],g1[5:0],g3[3:0],b1[4:0],b3[1],b2[3:0],r2[4:0], b3[2],r3[4:0],b3[3] 26 m[4:0],r0[7:0],b3[1],b2[4],g0[7:0],b2[5],g2[4],b0[7:0],b3[5],b3[4], r1[4:0],g3[4],g2[3:0],g1[4:0],b3[0],g3[3:0],b1[5:0],b2[3:0],r2[4:0], b3[2],r3[4:0],b3[3] 30 m[4:0],r0[5:0],g3[4],b3[0],b3[1],b2[4],g0[5:0],g2[5],b2[5],b3[2], g2[4],b0[5:0],g3[5],b3[3],b3[5],b3[4],r1[5:0],g2[3:0],g1[5:0],g3[3:0], b1[5:0],b2[3:0],r2[5:0],r3[5:0] 3 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[9:0],g1[9:0],b1[9:0] 7 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[8:0],r0[10],g1[8:0],g0[10],b1[8:0], b0[10] 11 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[7:0],r0[10:11],g1[7:0],g0[10:11], b1[7:0],b0[10:11] 15 m[4:0],r0[9:0],g0[9:0],b0[9:0],r1[3:0],r0[10:15],g1[3:0],g0[10:15], b1[3:0],b0[10:15] Issues (1) Are both RGB and RGBA versions interesting? RESOLVED. Not for the unorm formats. Every BPTC mode has a defined alpha, so an RGB mode isn't needed. Also, since modes are per-block, a given texture can have both RGB1 and RGBA portions. The float formats don't compress alpha at all, so they only have RGB variants, not RGBA. (2) Put both BC7 and BC6H in the same spec? RESOLVED. Yes. They share enough that it's worthwhile to amortize the "overhead". (3) Why are there two versions of the float BPTC formats for signed and unsigned? Do they pass through the GL differently? RESOLVED. The unsigned formats are decoded distinctly from signed formats, so it is necessary to distinguish between them. The values still pass through the shader and the pixel path as signed floats, but the interpretation of the compressed block changes as described. (4) Should the result of the compressed float formats be half floats or single floats? RESOLVED. The expansion from packed to half to float will be specified as part of the decompression process. (5) What should be expected for a driver compressor for these formats? RESOLVED: The current best known compression algorithms have to exhaustively test all partitionings across all modes. The compressor in the GL will have to make a tradeoff between performance and quality. Compressing offline is highly recommended. (6) How should floating point specials (Inf and NaN) be handled in the float formats? RESOLVED: Decompressor will never generate them. Compressor should flush to max half float. (7) Does this spec require bit-exact decompression? RESOLVED: Yes. (8) Does the data format depend on the endianness of the system? RESOLVED: No. The data is interpeted as an endian-independent byte stream. (9) What should be the internal format of the floating-point BPTC format? RESOLVED: The format has three components, with the alpha component mapped to 1.0, just like RGB textures. So we should call it RGB. In the originally ratified version of this extension (and all versions prior to January 20, 2011), such textures were treated as having a base internal format of RGBA, where the alpha component was not present in the texture and instead is just set to the constant 1.0. Some implementations of this extension may also use a base internal format of RGBA. There are very few places where there is a difference between an RGB texture and an RGBA texture where alpha is always 1.0. Two known differences: * A compressed "RGB" texture could be used for the generic COMPRESSED_RGB format, but an "RGBA" texture should not be. However, it seems unlikely that implementations would choose the floating-point BPTC format as its generic COMPRESSED_RGB format. * Using fixed-function fragment shading in the compatibility profile, a texture environment mode of REPLACE would leave alpha unmodified for RGB base formats but would replace the fragment alpha with the texture alpha (constant 1.0 here) for RGBA base formats. Revision History Rev. Date Author Changes ---- -------- ----------- -------------------------------------------- 9 30/10/19 pdaniell Fix shared p-bits specification to match DX and the Khronos Data Format spec. 8 06/06/16 Nanley Chery Reduce the requirements to the minimal set. 7 01/20/11 pbrown Change the base internal format of the floating- point BPTC formats from "RGBA" to "RGB" (bug 7231). 6 01/19/11 Jon Leech Fix state table modification for TEXTURE_INTERNAL_FORMAT (Bug 7239). 5 05/20/10 ewerness Finalize some UNRESOLVED issues 4 04/09/10 pdaniell Modify for inclusion into OpenGL 4.1. 3 12/07/09 pdaniell ARBify. 2 10/13/09 ewerness Fix errors in the anchor index tables caused by incorrect conversion scripts and a couple typos in the input. 1 ewerness Internal revisions.