Add UASTC HDR.

Makefile

@@ -22,6 +22,8 @@ ktx_inlined_images := icons/ktx_favicon.ico \
 appendices=appendices
 
 ktx_sources := ktxspec.adoc \
+           $(appendices)/basisuah66i-gdata.adoc \
+           $(appendices)/basisuah66i-bitstream.adoc \
            $(appendices)/basislz-gdata.adoc \
            $(appendices)/basislz-bitstream.adoc \
            $(appendices)/vendor-metadata.adoc \

appendices/basislz-gdata.adoc

@@ -3,7 +3,7 @@
 
 BasisLZ combines encoding to a block-compressed format, that can be easily transcoded to various GPU-native block-compressed formats, with lossless supercompression.  Supercompression is accomplished by conditioning the block-compressed representation for entropy encoding then Huffman encoding the result. BasisLZ creates a global codebook referenced by each supercompressed image that contains the processed endpoint and selector data from the block-compression and the Huffman tables. The global data block contains this codebook.
 
-It also contains an array of _image descriptors_ with flags for each image and the offset and length within the mip level of the data for that image.
+It also contains an array of _image descriptors_ with flags for each image and the offset within its mip level and length of the data for that image.
 
 The global data structure is designed to accommodate various transcodable block-compressed formats. The format in use is indicated by the <<_data_format_descriptor, Data Format Descriptor>>. Currently BasisLZ only supports one, <<etc1s, ETC1S>> (a subset of ETC1, see {url-df-spec}#ETC1S[Section 21.1] of <<KDF14>>).  ETC1S is a common subset of many GPU-native formats.
 
@@ -139,3 +139,4 @@ in <<ETC1S Slice Huffman Tables>>.
 === extendedData
 Extended data. This is not used for ETC1S.
 
+// vim: filetype=asciidoc ai expandtab tw=0 ts=4 sts=2 sw=2

appendices/basisuah66i-bitstream.adoc

@@ -0,0 +1,15 @@
+[appendix#basisuah66i]
+[#basisuah66i_bitstream]
+== Basis UASTC HDR 6x6 Intermediate Bitstream Specification
+
+_Basis UASTC HDR 6x6 Intermediate_ is a custom supercompression scheme for the Basis UASTC HDR 6x6 texture format.
+
+The bitstream is as documented in the https://github.com/BinomialLLC/basis_universal/wiki/UASTC-HDR-6x6-Intermediate-File-Format-(Basis-GPU-Photo-6x6)[format specification] on the basis_universal Wiki.
+The compression type is signalled by `supercompressionScheme` = 4 and `colorModel` = 168.
+The bitstream has a https://github.com/BinomialLLC/basis_universal/wiki/UASTC-HDR-6x6-Intermediate-File-Format-(Basis-GPU-Photo-6x6)#header[header] of 3 little-endian 16-bit fields.
+The first field is a combined ID field containing the entropy profile and stream semantic version with the profile ID in bits 15-8 (the second byte) and the stream semantic version in bits 7-0 (the first byte).
+This field must match the least significant 16-bits of (the first two bytes) of `rgbSliceType` in the <<basisuah66i_image_desc,ImageDesc>> that refers to the bitstream.
+The second and third fields are the width and height of the texture image in pixels.
+The value of the width field must equal stem:[\textit{num_blocks_x}] and the value of the height field must equal stem:[\textit{num_blocks_y}] as calculated for the mip level using <<levelImages_defs,these formulae>>. Since the width and height are in pixels, stem:[\textit{block_width}] and stem:[\textit{block_height}] in those formulae must be stem:[1].
+
+// vim: filetype=asciidoc ai expandtab tw=0 ts=4 sts=2 sw=2

appendices/basisuah66i-gdata.adoc

@@ -0,0 +1,77 @@
+[appendix#basisuah66i_gd]
+== Basis UASTC HDR 6x6 Intermediate Global Data
+
+Basis UASTC HDR 6x6 Intermediate format combines encoding to the UASTC HDR 6x6 subset of ASTC, that can be easily transcoded to BC6H unsigned, with lossless supercompression.
+The format uses a small number of variable bit length command codes which can output one or more blocks, and which can reuse parts of previously encoded blocks.
+Because of the variable size of each image Basis UASTC HDR 6x6 Intermediate creates a global data structure that contains an array of _image descriptors_ with the offset within its mip level and the length of the data for that image.
+
+
+[[basisuah66i_global_data_structure]]
+.Basis UASTC HDR 6x6 Global Data Structure
+[source,c,subs="+quotes,+attributes,+replacements"]
+----
+ImageDesc[imageCount] imageDescs;
+----
+
+`ImageDesc` is the following structure.
+
+.ImageDesc
+[source,c]
+----
+UInt32 rgbSliceByteOffset
+UInt32 rgbSliceByteLength
+UInt32 rgbSliceType
+----
+
+Descriptions in the `imageDescs` array are in the order layer, face and z_slice as if arranged by the following pseudo code.
+[source,c]
+----
+for each level in max(levelCount, 1)
+    for each layer in max (layerCount, 1)
+        for each face in faceCount // 1 or 6
+            for each z_slice in max((pixelDepth of level), 1)
+----
+
+`imageCount` is the total number of images in the Mip Level Array.
+
+[TIP]
+====
+`imageCount` may be calculated as follows:
+[source,c]
+----
+int imageCount = max(layerCount, 1) * faceCount * layerPixelDepth;
+
+// where layerPixelDepth can be derived as
+int layerPixelDepth = max(pixelDepth, 1);
+for(int i = 1; i < levelCount; i++)
+    layerPixelDepth += max(pixelDepth >> i, 1);
+----
+====
+
+There must be no trailing bytes in the global data section after the array of image descriptors, i.e., the following condition must always be true:
+[source,c]
+----
+sgdByteLength == imageCount * 12
+----
+
+[[basisuah66i_image_desc]]
+=== ImageDesc
+==== rgbSliceByteOffset, rgbSliceByteLength
+The offset of the start of the RGB slice within the <<levelImagesDesc,levelImages>> of its mip level and its byte length. The offset of <<levelImagesDesc,levelImages>> within the file is given in the <<_level_index,Level Index>>.
+
+`rgbSliceByteLength` must not be zero.
+
+`rgbSliceByteOffset + rgbSliceByteLength` must not be greater than the byte length of the corresponding mip level.
+
+[[basisuah66i_rgbSliceType]]
+==== rgbSliceType
+The combined ID field containing the entropy profile and stream semantic version used in the bitstream for this slice.
+The least significant 16-bits (the first two bytes) of this value must equal the first 16-bits of the bitstream for this slice as described in the https://github.com/BinomialLLC/basis_universal/wiki/UASTC-HDR-6x6-Intermediate-File-Format-(Basis-GPU-Photo-6x6)#header[header section] of the bitstream specification.
+The most significant 16-bits (the last two bytes) must be 0.
+[NOTE]
+.Rationale
+====
+Implementations can use this field to check for an unsupported version without having to load the data.
+====
+
+// vim: filetype=asciidoc ai expandtab tw=0 ts=4 sts=2 sw=2

docinfo.html

@@ -4,11 +4,15 @@
   /* Put Khronos ribbon on left side */
   background-attachment: fixed;
   background-image: url(images/logo-spec.svg);
-  background-position: left top;
+  background-position: right top;
   background-repeat: no-repeat/*, no-repeat*/;
-  /* Override default Asciidoctor margin settings to center the page. */
-  margin: 2em auto 2em auto;
-  max-width: 60em;
+  /* If wider than in #content below, this adds extra margin. */
+  max-width: 100em;
+}
+
+#content {
+  /* Override max from khronos.css. */
+  max-width: 62.5em
 }
 
 div.legal p {