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v2.1 update for KTX-Software and Khronos file format KTX2 compatibility.

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This update impacts the UASTC HDR 4x4, UASTC HDR 6x6i, and XUASTC LDR formats. New KTX2 files in these specific formats using v2.1 can't be loaded using v2.0, however we've kept backwards compatibility with all of our previously written KTX2 files. (v2.1 can transcode all previously written files.)
This is part of our effort to be compatible with Khronos's specification.
bc6hf encoder's smooth block path updated to handle inputs with texels close to MAX_HALF_FLOAT.
Adding command line options to basisu tool so it can write either v2.0 or v1.6 compatible UASTC HDR 6x6i files. The default is v1.6.
Updating WebGL KTX2 testbed so on ASTC devices it automatically switches between sRGB or linear internal formats for the created texture.
This commit is contained in:
Richard Geldreich
2026-02-24 20:35:11 -05:00
parent 2c4f52f705
commit 81a4186404
34 changed files with 499 additions and 234 deletions
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211
transcoder/basisu_transcoder.cpp
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@@ -19504,13 +19504,21 @@ namespace basist
return false;
}
if (m_header.m_supercompression_scheme > KTX2_SS_ZSTANDARD)
if ((m_header.m_supercompression_scheme == KTX2_SS_UASTC_HDR_6x6I) ||
(m_header.m_supercompression_scheme == KTX2_SS_XUASTC_LDR))
{
// standard UASTC HDR 6x6i file (as adopted by khronos, not our initial v1.6/v2.0 release), or XUASTC LDR - DFD colormodels unchanged however
}
else if (m_header.m_supercompression_scheme > KTX2_SS_ZSTANDARD)
{
BASISU_DEVEL_ERROR("ktx2_transcoder::init: Invalid/unsupported supercompression or file is corrupted or invalid\n");
return false;
}
if (m_header.m_supercompression_scheme == KTX2_SS_BASISLZ)
// Sanity check SGD offset/length
if ((m_header.m_supercompression_scheme == KTX2_SS_BASISLZ) ||
(m_header.m_supercompression_scheme == KTX2_SS_UASTC_HDR_6x6I) ||
(m_header.m_supercompression_scheme == KTX2_SS_XUASTC_LDR))
{
if (m_header.m_sgd_byte_offset.get_uint64() < sizeof(ktx2_header))
{
@@ -19569,16 +19577,20 @@ namespace basist
return false;
}
if (m_header.m_supercompression_scheme == KTX2_SS_BASISLZ)
if ((m_header.m_supercompression_scheme == KTX2_SS_BASISLZ) ||
(m_header.m_supercompression_scheme == KTX2_SS_UASTC_HDR_6x6I) ||
(m_header.m_supercompression_scheme == KTX2_SS_XUASTC_LDR))
{
// Our supercompressed codec formats: Uncompressed length should be 0
if (m_levels[i].m_uncompressed_byte_length.get_uint64())
{
BASISU_DEVEL_ERROR("ktx2_transcoder::init: Invalid uncompressed length (0)\n");
return false;
}
}
else if (m_header.m_supercompression_scheme >= KTX2_SS_ZSTANDARD)
else if (m_header.m_supercompression_scheme == KTX2_SS_ZSTANDARD)
{
// Uses Zstandard supercompression, ensure uncompressed length is valid.
if (!m_levels[i].m_uncompressed_byte_length.get_uint64())
{
BASISU_DEVEL_ERROR("ktx2_transcoder::init: Invalid uncompressed length (1)\n");
@@ -19775,6 +19787,8 @@ namespace basist
}
else if (m_dfd_color_model == KTX2_KDF_DF_MODEL_UASTC_HDR_6X6_INTERMEDIATE)
{
// Note: The supercompression scheme may be BASISLZ if it's an old format (v1.6/v2.0) file
// Custom variable block size ASTC HDR 6x6 texture data.
if (m_header.m_vk_format != basist::KTX2_VK_FORMAT_UNDEFINED)
{
@@ -19902,6 +19916,8 @@ namespace basist
return false;
}
// In standard KTX2 file, KTX2_SS_BASISLZ would ONLY be ETC1S, but in v1.6 and v2.0 it could also mean UASTC HDR 6x6i or XUASTC LDR.
// We support our older files, too.
if (m_header.m_supercompression_scheme == KTX2_SS_BASISLZ)
{
if (m_format == basis_tex_format::cETC1S)
@@ -19933,13 +19949,14 @@ namespace basist
}
}
}
// check for old-style (non-standard) KTX2 files written by v1.6/v2.0
else if ( (m_format == basis_tex_format::cUASTC_HDR_6x6_INTERMEDIATE) || basis_tex_format_is_xuastc_ldr(m_format) )
{
// UASTC HDR 6x6 and XUASTC LDR 4x4-12x12 require an array of slice offset/len structs to determine where the compressed data starts for each independent compressed texture slice.
if (m_slice_offset_len_descs.size())
return true;
if (!read_slice_offset_len_global_data())
if (!read_slice_offset_len_global_data(false))
{
BASISU_DEVEL_ERROR("ktx2_transcoder::start_transcoding: read_slice_offset_len_global_data() failed\n");
return false;
@@ -19951,6 +19968,18 @@ namespace basist
return false;
}
}
else if ((m_header.m_supercompression_scheme == KTX2_SS_UASTC_HDR_6x6I) || (m_header.m_supercompression_scheme == KTX2_SS_XUASTC_LDR))
{
// UASTC HDR 6x6 and XUASTC LDR 4x4-12x12 require an array of slice offset/len structs to determine where the compressed data starts for each independent compressed texture slice.
if (m_slice_offset_len_descs.size())
return true;
if (!read_slice_offset_len_global_data(true))
{
BASISU_DEVEL_ERROR("ktx2_transcoder::start_transcoding: read_slice_offset_len_global_data() failed\n");
return false;
}
}
else if (m_header.m_supercompression_scheme == KTX2_SS_ZSTANDARD)
{
#if !BASISD_SUPPORT_KTX2_ZSTD
@@ -20143,7 +20172,7 @@ namespace basist
}
else if (m_format == basist::basis_tex_format::cUASTC_HDR_6x6_INTERMEDIATE)
{
// UASTC HDR 6x6
// UASTC HDR 6x6i
if (!m_slice_offset_len_descs.size())
{
BASISU_DEVEL_ERROR("ktx2_transcoder::transcode_image_level: must call start_transcoding() first\n");
@@ -20165,7 +20194,7 @@ namespace basist
return false;
}
const ktx2_slice_offset_len_desc& image_desc = m_slice_offset_len_descs[image_index];
const ktx2_slice_offset_len_desc_orig& image_desc = m_slice_offset_len_descs[image_index];
if (!m_astc_hdr_6x6_intermediate_transcoder.transcode_image(fmt,
pOutput_blocks, output_blocks_buf_size_in_blocks_or_pixels,
@@ -20301,7 +20330,7 @@ namespace basist
return false;
}
const ktx2_slice_offset_len_desc& image_desc = m_slice_offset_len_descs[image_index];
const ktx2_slice_offset_len_desc_orig& image_desc = m_slice_offset_len_descs[image_index];
// XUASTC LDR has its own tiny header at the start of the compressed data with this profile bit, so it'll use that for decoding if needed.
bool uses_astc_src_decode_profile = true;
@@ -20436,22 +20465,43 @@ namespace basist
return true;
}
bool ktx2_transcoder::read_slice_offset_len_global_data()
bool ktx2_transcoder::read_slice_offset_len_global_data(bool read_std_structs)
{
const uint32_t image_count = basisu::maximum<uint32_t>(m_header.m_layer_count, 1) * m_header.m_face_count * m_header.m_level_count;
assert(image_count);
const uint8_t* pSrc = m_pData + m_header.m_sgd_byte_offset.get_uint64();
if (m_header.m_sgd_byte_length.get_uint64() != image_count * sizeof(ktx2_slice_offset_len_desc))
{
BASISU_DEVEL_ERROR("ktx2_transcoder::read_slice_offset_len_global_data: Invalid global data length\n");
return false;
}
m_slice_offset_len_descs.resize(image_count);
memcpy((void *)m_slice_offset_len_descs.data(), pSrc, sizeof(ktx2_slice_offset_len_desc) * image_count);
// SGD offset/length already sanity checked to be inside the file and after the KTX2 header.
if (read_std_structs)
{
if (m_header.m_sgd_byte_length.get_uint64() != image_count * sizeof(ktx2_slice_offset_len_desc_std))
{
BASISU_DEVEL_ERROR("ktx2_transcoder::read_slice_offset_len_global_data: Invalid global data length (0)\n");
return false;
}
const ktx2_slice_offset_len_desc_std* pSrc_std_descs = reinterpret_cast<const ktx2_slice_offset_len_desc_std*>(pSrc);
for (uint32_t i = 0; i < image_count; i++)
{
// TODO: Ignoring type (profile) for now, but we could check it
m_slice_offset_len_descs[i].m_slice_byte_offset = pSrc_std_descs[i].m_slice_byte_offset;
m_slice_offset_len_descs[i].m_slice_byte_length = pSrc_std_descs[i].m_slice_byte_length;
}
}
else
{
if (m_header.m_sgd_byte_length.get_uint64() != image_count * sizeof(ktx2_slice_offset_len_desc_orig))
{
BASISU_DEVEL_ERROR("ktx2_transcoder::read_slice_offset_len_global_data: Invalid global data length (1)\n");
return false;
}
memcpy((void*)m_slice_offset_len_descs.data(), pSrc, sizeof(ktx2_slice_offset_len_desc_orig) * image_count);
}
// Sanity check the image descs
for (uint32_t i = 0; i < image_count; i++)
@@ -22952,52 +23002,7 @@ namespace basist
static const int FAST_BC6H_STD_DEV_THRESH = 256;
static const int FAST_BC6H_COMPLEX_STD_DEV_THRESH = 512;
static const int FAST_BC6H_VERY_COMPLEX_STD_DEV_THRESH = 2048;
static void assign_weights_simple_4(
const basist::half_float* pPixels,
uint8_t* pWeights,
int min_r, int min_g, int min_b,
int max_r, int max_g, int max_b, int64_t block_max_var)
{
BASISU_NOTE_UNUSED(block_max_var);
float fmin_r = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)min_r);
float fmin_g = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)min_g);
float fmin_b = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)min_b);
float fmax_r = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)max_r);
float fmax_g = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)max_g);
float fmax_b = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)max_b);
float fdir_r = fmax_r - fmin_r;
float fdir_g = fmax_g - fmin_g;
float fdir_b = fmax_b - fmin_b;
float l = inv_sqrt(fdir_r * fdir_r + fdir_g * fdir_g + fdir_b * fdir_b);
if (l != 0.0f)
{
fdir_r *= l;
fdir_g *= l;
fdir_b *= l;
}
float lr = ftoh(fmin_r * fdir_r + fmin_g * fdir_g + fmin_b * fdir_b);
float hr = ftoh(fmax_r * fdir_r + fmax_g * fdir_g + fmax_b * fdir_b);
float frr = (hr == lr) ? 0.0f : (14.93333f / (float)(hr - lr));
lr = (-lr * frr) + 0.53333f;
for (uint32_t i = 0; i < 16; i++)
{
const float r = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 0]);
const float g = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 1]);
const float b = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 2]);
const float w = ftoh(r * fdir_r + g * fdir_g + b * fdir_b);
pWeights[i] = (uint8_t)basisu::clamp((int)(w * frr + lr), 0, 15);
}
}
static double assign_weights_4(
const vec3F* pFloat_pixels, const float* pPixel_scales,
uint8_t* pWeights,
@@ -23187,6 +23192,80 @@ namespace basist
return total_err;
}
static void assign_weights_simple_4(
const basist::half_float* pPixels,
uint8_t* pWeights,
int min_r, int min_g, int min_b,
int max_r, int max_g, int max_b, int64_t block_max_var,
const fast_bc6h_params& params)
{
BASISU_NOTE_UNUSED(block_max_var);
float fmin_r = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)min_r);
float fmin_g = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)min_g);
float fmin_b = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)min_b);
float fmax_r = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)max_r);
float fmax_g = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)max_g);
float fmax_b = fast_half_to_float_pos_not_inf_or_nan((basist::half_float)max_b);
float fdir_r = fmax_r - fmin_r;
float fdir_g = fmax_g - fmin_g;
float fdir_b = fmax_b - fmin_b;
float l = inv_sqrt(fdir_r * fdir_r + fdir_g * fdir_g + fdir_b * fdir_b);
if (l != 0.0f)
{
fdir_r *= l;
fdir_g *= l;
fdir_b *= l;
}
float lf = fmin_r * fdir_r + fmin_g * fdir_g + fmin_b * fdir_b;
float hf = fmax_r * fdir_r + fmax_g * fdir_g + fmax_b * fdir_b;
if ((lf >= basist::MAX_HALF_FLOAT) || (hf >= basist::MAX_HALF_FLOAT))
{
// v2.1: Can't use the faster half float based tricks below, need some sort of backup
vec3F float_pixels[16];
float pixel_scales[16];
for (uint32_t i = 0; i < 16; i++)
{
float_pixels[i].c[0] = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 0]);
float_pixels[i].c[1] = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 1]);
float_pixels[i].c[2] = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 2]);
pixel_scales[i] = 1.0f / (basisu::squaref(float_pixels[i].c[0]) + basisu::squaref(float_pixels[i].c[1]) + basisu::squaref(float_pixels[i].c[2]) + (float)MIN_HALF_FLOAT);
}
assign_weights_4(
float_pixels, pixel_scales,
pWeights,
min_r, min_g, min_b,
max_r, max_g, max_b, block_max_var, false,
params);
return;
}
float lr = ftoh(lf);
float hr = ftoh(hf);
float frr = (hr == lr) ? 0.0f : (14.93333f / (float)(hr - lr));
lr = (-lr * frr) + 0.53333f;
for (uint32_t i = 0; i < 16; i++)
{
const float r = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 0]);
const float g = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 1]);
const float b = fast_half_to_float_pos_not_inf_or_nan(pPixels[i * 3 + 2]);
const float w = ftoh(r * fdir_r + g * fdir_g + b * fdir_b);
pWeights[i] = (uint8_t)basisu::clamp((int)(w * frr + lr), 0, 15);
}
}
static void assign_weights3(uint8_t trial_weights[16],
uint32_t best_pat_bits,
uint32_t subset_min_r[2], uint32_t subset_min_g[2], uint32_t subset_min_b[2],
@@ -23947,8 +24026,8 @@ namespace basist
bc6h_quant_dequant_endpoints(min_r, min_g, min_b, max_r, max_g, max_b, 10);
assign_weights_simple_4(pPixels, log_blk.m_weights, min_r, min_g, min_b, max_r, max_g, max_b, block_max_var);
assign_weights_simple_4(pPixels, log_blk.m_weights, min_r, min_g, min_b, max_r, max_g, max_b, block_max_var, params);
log_blk.m_endpoints[0][0] = basist::bc6h_half_to_blog((basist::half_float)min_r, 10);
log_blk.m_endpoints[0][1] = basist::bc6h_half_to_blog((basist::half_float)max_r, 10);