Update to BasisU 2.0

[MarkCallow]

Just a few lines of code changed due to basisu_encoder API changes plus some golden files regenerated due to a different version of zstd being included.

[solbjorn]

The diff outside external/ folder after rebasing the PR onto the latest commit (with HDR):

diff --git a/interface/js_binding/transcoder_wrapper.cpp b/interface/js_binding/transcoder_wrapper.cpp
index b54b8aaab7c5..71609f33b6ad 100644
--- a/interface/js_binding/transcoder_wrapper.cpp
+++ b/interface/js_binding/transcoder_wrapper.cpp
@@ -465,7 +465,7 @@ enum TranscodeTarget = {
 
 enum TextureFormat = {
     "ETC1S",
-    "UASTC4x4",
+    "UASTC_LDR_4x4",
 };
 
 enum TranscodeFlagBits =
@@ -525,7 +525,7 @@ container format.
     // Determine from the KTX2 header information in buData if
     // the data format  is BasisU or Uastc.
     // supercompressionScheme value == 1, it's TextureFormat.ETC1S.
-    // DFD colorModel == 166, it's TextureFormat.UASTC4x4.
+    // DFD colorModel == 166, it's TextureFormat.UASTC_LDR_4x4.
     const texFormat = ...
 
     // Determine appropriate transcode format from available targets,
@@ -536,7 +536,7 @@ container format.
         throw new Error( ... );
     }
 
-    if (TextureFormat.UASTC4x4) {
+    if (TextureFormat.UASTC_LDR_4x4) {
         var result = transcodeUastc(targetFormat);
     } else {
         var result = transcodeEtc1s(targetFormat);
@@ -676,7 +676,7 @@ transcodeUastc(targetFormat) {
       var levelImageCount = number of layers * number of faces * depth;
       var imageOffsetInLevel = 0;
 
-      var imageInfo = new ImageInfo(TextureFormat::UASTC4x4,
+      var imageInfo = new ImageInfo(TextureFormat::UASTC_LDR_4x4,
                                     levelWidth, levelHeight, level);
       var levelImageByteLength = imageInfo.numBlocksX * imageInfo.numBlocksY * DFD bytesPlane0;
 
@@ -746,7 +746,9 @@ EMSCRIPTEN_BINDINGS(ktx_wrappers)
 
     enum_<basis_tex_format>("TextureFormat")
         .value("ETC1S", basis_tex_format::cETC1S)
-        .value("UASTC4x4", basis_tex_format::cUASTC4x4)
+        .value("UASTC_LDR_4x4", basis_tex_format::cUASTC_LDR_4x4)
+        // For backward compatibility
+        .value("UASTC4x4", basis_tex_format::cUASTC_LDR_4x4)
     ;
 
     enum_<msc::TranscodeFlagBits>("TranscodeFlagBits")
diff --git a/lib/src/basis_encode.cpp b/lib/src/basis_encode.cpp
index 4c533e654106..23f42015f6fa 100644
--- a/lib/src/basis_encode.cpp
+++ b/lib/src/basis_encode.cpp
@@ -647,7 +647,7 @@ ktxTexture2_CompressBasisEx(ktxTexture2* This, ktxBasisParams* params)
     case ktx_basis_codec_e::KTX_BASIS_CODEC_UASTC_HDR_6X6_INTERMEDIATE:
         cparams.m_uastc = true;
         cparams.m_hdr = true;
-        cparams.m_hdr_mode = basisu::hdr_modes::cASTC_HDR_6X6_INTERMEDIATE;
+        cparams.m_hdr_mode = basisu::hdr_modes::cUASTC_HDR_6X6_INTERMEDIATE;
         break;
     default:
         break;
@@ -867,10 +867,12 @@ ktxTexture2_CompressBasisEx(ktxTexture2* This, ktxBasisParams* params)
     ktx_uint32_t transfer = KHR_DFDVAL(BDB, TRANSFER);
     if (transfer == KHR_DF_TRANSFER_SRGB) {
         cparams.m_perceptual = true;
-        cparams.m_ktx2_srgb_transfer_func = true;
+        cparams.m_ktx2_and_basis_srgb_transfer_function = true;
     }
-    else
+    else {
         cparams.m_perceptual = false;
+        cparams.m_ktx2_and_basis_srgb_transfer_function = false;
+    }
 
     cparams.m_mip_gen = false; // We provide the mip levels.
     
@@ -917,7 +919,7 @@ ktxTexture2_CompressBasisEx(ktxTexture2* This, ktxBasisParams* params)
         // indicate the parameter has not been set by the caller. (If we
         // leave m_compression_level unset it will default to 1. We don't
         // want the default to differ from `basisu` so 0 can't be the default.
-        cparams.m_compression_level = params->etc1sCompressionLevel;
+        cparams.m_etc1s_compression_level = params->etc1sCompressionLevel;
 
         // There's no default for m_quality_level. `basisu` tool overrides
         // any explicit m_{endpoint,selector}_clusters settings with those
@@ -941,11 +943,11 @@ ktxTexture2_CompressBasisEx(ktxTexture2* This, ktxBasisParams* params)
         } else if (params->qualityLevel != 0) {
             cparams.m_etc1s_max_endpoint_clusters = 0;
             cparams.m_etc1s_max_selector_clusters = 0;
-            cparams.m_etc1s_quality_level = params->qualityLevel;
+            cparams.m_quality_level = params->qualityLevel;
         } else {
             cparams.m_etc1s_max_endpoint_clusters = 0;
             cparams.m_etc1s_max_selector_clusters = 0;
-            cparams.m_etc1s_quality_level = 128;
+            cparams.m_quality_level = 128;
         }
 
         if (params->endpointRDOThreshold > 0)
@@ -1089,7 +1091,7 @@ ktxTexture2_CompressBasisEx(ktxTexture2* This, ktxBasisParams* params)
     std::vector<uint32_t> level_file_offsets(This->numLevels);
 
     if (cparams.m_uastc) {
-        if (cparams.m_hdr && cparams.m_hdr_mode == hdr_modes::cASTC_HDR_6X6_INTERMEDIATE) {
+        if (cparams.m_hdr && cparams.m_hdr_mode == hdr_modes::cUASTC_HDR_6X6_INTERMEDIATE) {
             uint32_t image_desc_size = sizeof(ktxUASTCHDR6X6IntermediateImageDesc);
             bgd_size = image_desc_size * num_images;
             bgd = new ktx_uint8_t[bgd_size];
@@ -1356,7 +1358,7 @@ cleanup:
 }
 
 extern "C" KTX_API const ktx_uint32_t KTX_ETC1S_DEFAULT_COMPRESSION_LEVEL
-                                      = BASISU_DEFAULT_COMPRESSION_LEVEL;
+                                           = BASISU_DEFAULT_ETC1S_COMPRESSION_LEVEL;
 
 /**
  * @memberof ktxTexture2
diff --git a/lib/src/basis_transcode.cpp b/lib/src/basis_transcode.cpp
index c9cf31d4f7f1..7c5ed05f66cc 100644
--- a/lib/src/basis_transcode.cpp
+++ b/lib/src/basis_transcode.cpp
@@ -343,11 +343,11 @@ ktx2transcoderFormat(ktx_transcode_fmt_e ktx_fmt) {
 
     basis_tex_format textureFormat;
     if (colorModel == KHR_DF_MODEL_UASTC)
-        textureFormat = basis_tex_format::cUASTC4x4;
+        textureFormat = basis_tex_format::cUASTC_LDR_4x4;
     else if (colorModel == KHR_DF_MODEL_UASTC_HDR_4X4)
         textureFormat = basis_tex_format::cUASTC_HDR_4x4;        
     else if (colorModel == KHR_DF_MODEL_UASTC_HDR_6X6)
-        textureFormat = basis_tex_format::cASTC_HDR_6x6_INTERMEDIATE;    
+        textureFormat = basis_tex_format::cUASTC_HDR_6x6_INTERMEDIATE;    
     else
         textureFormat = basis_tex_format::cETC1S;
 
@@ -911,7 +911,7 @@ transcodeUastcHDR6x6_intermediate(ktxTexture2* This, alpha_content_e alphaConten
     ktxLevelIndexEntry* protoLevelIndex = protoPriv._levelIndex;
     ktx_size_t levelOffsetWrite = 0;
 
-    basist::basisu_lowlevel_astc_hdr_6x6_intermediate_transcoder uit;
+    basist::basisu_lowlevel_uastc_hdr_6x6_intermediate_transcoder uit;
     // See comment on same declaration in transcodeEtc1s.
     std::vector<basisu_transcoder_state> xcoderStates;
     xcoderStates.resize(This->isVideo ? This->numFaces : 1);
diff --git a/tests/webgl/llt-three/KTX2Loader.js b/tests/webgl/llt-three/KTX2Loader.js
index a3681417428d..eba93625f6ad 100644
--- a/tests/webgl/llt-three/KTX2Loader.js
+++ b/tests/webgl/llt-three/KTX2Loader.js
@@ -138,13 +138,13 @@ class KTX2Loader extends CompressedTextureLoader {
 // colorModel is ETC1S (163) or if dfd colorModel is UASTCF (166)
 // then texture must be transcoded.
 
-		var texFormat = ktx.dfd.colorModel == DFD.modelUastc ? TextureFormat.UASTC4x4
+		var texFormat = ktx.dfd.colorModel == DFD.modelUastc ? TextureFormat.UASTC_LDR_4x4
 												   : TextureFormat.ETC1S;
 		// TODO(donmccurdy): Handle all channelIds (i.e. the R & R+G cases),
 		// choosing appropriate transcode target formats or providing queries
 		// for applications so they know what to do with the content.
 		var hasAlpha = false;
-		if (texFormat == TextureFormat.UASTC4x4) {
+		if (texFormat == TextureFormat.UASTC_LDR_4x4) {
 			var transcoder = new UastcImageTranscoder();
 			if ( (ktx.dfd.samples[0].channelId & 0xf) === DFD.channelUastc.rgba )
 				hasAlpha = true;
@@ -419,7 +419,7 @@ class KTX2Container {
 
 		var isVideo = false;
 
-		// For both ETC1S and UASTC4x4 formats.
+		// For both ETC1S and UASTC_LDR_4x4 formats.
 		if ( texFormat == TextureFormat.ETC1S ) {
 			var numEndpoints = this.sgd.endpointCount;
 			var numSelectors = this.sgd.selectorCount;
@@ -483,7 +483,7 @@ class KTX2Container {
 			for ( var imageIndex = 0; imageIndex < numImagesInLevel; imageIndex ++ ) {
 
 				var result;
-				if ( texFormat == TextureFormat.UASTC4x4 ) {
+				if ( texFormat == TextureFormat.UASTC_LDR_4x4 ) {
 					imageInfo.flags = 0;
 					imageInfo.rgbByteOffset = 0;
 					imageInfo.rgbByteLength = levelImageByteLength;

Note the explicit initialization of m_ktx2_and_basis_srgb_transfer_function -- in BasisU 2, it's true by default, so setting it to false is necessary.

I can't say it accounts everything, but I haven't spotted any regressions so far.