// SPDX-License-Identifier: Apache-2.0
// ----------------------------------------------------------------------------
// Copyright 2011-2022 Arm Limited
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy
// of the License at:
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations
// under the License.
// ----------------------------------------------------------------------------
#if !defined(ASTCENC_DECOMPRESS_ONLY)
/**
* @brief Functions for finding best endpoint format.
*
* We assume there are two independent sources of error in any given partition:
*
* - Encoding choice errors
* - Quantization errors
*
* Encoding choice errors are caused by encoder decisions. For example:
*
* - Using luminance instead of separate RGB components.
* - Using a constant 1.0 alpha instead of storing an alpha component.
* - Using RGB+scale instead of storing two full RGB endpoints.
*
* Quantization errors occur due to the limited precision we use for storage. These errors generally
* scale with quantization level, but are not actually independent of color encoding. In particular:
*
* - If we can use offset encoding then quantization error is halved.
* - If we can use blue-contraction then quantization error for RG is halved.
* - If we use HDR endpoints the quantization error is higher.
*
* Apart from these effects, we assume the error is proportional to the quantization step size.
*/
#include "astcenc_internal.h"
#include "astcenc_vecmathlib.h"
#include <assert.h>
/**
* @brief Compute the errors of the endpoint line options for one partition.
*
* Uncorrelated data assumes storing completely independent RGBA channels for each endpoint. Same
* chroma data assumes storing RGBA endpoints which pass though the origin (LDR only). RGBL data
* assumes storing RGB + lumashift (HDR only). Luminance error assumes storing RGB channels as a
* single value.
*
*
* @param pi The partition info data.
* @param partition_index The partition index to compule the error for.
* @param blk The image block.
* @param uncor_pline The endpoint line assuming uncorrelated endpoints.
* @param[out] uncor_err The computed error for the uncorrelated endpoint line.
* @param samec_pline The endpoint line assuming the same chroma for both endpoints.
* @param[out] samec_err The computed error for the uncorrelated endpoint line.
* @param rgbl_pline The endpoint line assuming RGB + lumashift data.
* @param[out] rgbl_err The computed error for the RGB + lumashift endpoint line.
* @param l_pline The endpoint line assuming luminance data.
* @param[out] l_err The computed error for the luminance endpoint line.
* @param[out] a_drop_err The computed error for dropping the alpha component.
*/
static void compute_error_squared_rgb_single_partition(
const partition_info& pi,
int partition_index,
const image_block& blk,
const processed_line3& uncor_pline,
float& uncor_err,
const processed_line3& samec_pline,
float& samec_err,
const processed_line3& rgbl_pline,
float& rgbl_err,
const processed_line3& l_pline,
float& l_err,
float& a_drop_err
) {
vfloat4 ews = blk.channel_weight;
unsigned int texel_count = pi.partition_texel_count[partition_index];
const uint8_t* texel_indexes = pi.texels_of_partition[partition_index];
promise(texel_count > 0);
vfloatacc a_drop_errv = vfloatacc::zero();
vfloat default_a(blk.get_default_alpha());
vfloatacc uncor_errv = vfloatacc::zero();
vfloat uncor_bs0(uncor_pline.bs.lane<0>());
vfloat uncor_bs1(uncor_pline.bs.lane<1>());
vfloat uncor_bs2(uncor_pline.bs.lane<2>());
vfloat uncor_amod0(uncor_pline.amod.lane<0>());
vfloat uncor_amod1(uncor_pline.amod.lane<1>());
vfloat uncor_amod2(uncor_pline.amod.lane<2>());
vfloatacc samec_errv = vfloatacc::zero();
vfloat samec_bs0(samec_pline.bs.lane<0>());
vfloat samec_bs1(samec_pline.bs.lane<1>());
vfloat samec_bs2(samec_pline.bs.lane<2>());
vfloatacc rgbl_errv = vfloatacc::zero();
vfloat rgbl_bs0(rgbl_pline.bs.lane<0>());
vfloat rgbl_bs1(rgbl_pline.bs.lane<1>());
vfloat rgbl_bs2(rgbl_pline.bs.lane<2>());
vfloat rgbl_amod0(rgbl_pline.amod.lane<0>());
vfloat rgbl_amod1(rgbl_pline.amod.lane<1>());
vfloat rgbl_amod2(rgbl_pline.amod.lane<2>());
vfloatacc l_errv = vfloatacc::zero();
vfloat l_bs0(l_pline.bs.lane<0>());
vfloat l_bs1(l_pline.bs.lane<1>());
vfloat l_bs2(l_pline.bs.lane<2>());
vint lane_ids = vint::lane_id();
for (unsigned int i = 0; i < texel_count; i += ASTCENC_SIMD_WIDTH)
{
vint tix(texel_indexes + i);
vmask mask = lane_ids < vint(texel_count);
lane_ids += vint(ASTCENC_SIMD_WIDTH);
// Compute the error that arises from just ditching alpha
vfloat data_a = gatherf(blk.data_a, tix);
vfloat alpha_diff = data_a - default_a;
alpha_diff = alpha_diff * alpha_diff;
haccumulate(a_drop_errv, alpha_diff, mask);
vfloat data_r = gatherf(blk.data_r, tix);
vfloat data_g = gatherf(blk.data_g, tix);
vfloat data_b = gatherf(blk.data_b, tix);
// Compute uncorrelated error
vfloat param = data_r * uncor_bs0
+ data_g * uncor_bs1
+ data_b * uncor_bs2;
vfloat dist0 = (uncor_amod0 + param * uncor_bs0) - data_r;
vfloat dist1 = (uncor_amod1 + param * uncor_bs1) - data_g;
vfloat dist2 = (uncor_amod2 + param * uncor_bs2) - data_b;
vfloat error = dist0 * dist0 * ews.lane<0>()
+ dist1 * dist1 * ews.lane<1>()
+ dist2 * dist2 * ews.lane<2>();
haccumulate(uncor_errv, error, mask);
// Compute same chroma error - no "amod", its always zero
param = data_r * samec_bs0
+ data_g * samec_bs1
+ data_b * samec_bs2;
dist0 = (param * samec_bs0) - data_r;
dist1 = (param * samec_bs1) - data_g;
dist2 = (param * samec_bs2) - data_b;
error = dist0 * dist0 * ews.lane<0>()
+ dist1 * dist1 * ews.lane<1>()
+ dist2 * dist2 * ews.lane<2>();
haccumulate(samec_errv, error, mask);
// Compute rgbl error
param = data_r * rgbl_bs0
+ data_g * rgbl_bs1
+ data_b * rgbl_bs2;
dist0 = (rgbl_amod0 + param * rgbl_bs0) - data_r;
dist1 = (rgbl_amod1 + param * rgbl_bs1) - data_g;
dist2 = (rgbl_amod2 + param * rgbl_bs2) - data_b;
error = dist0 * dist0 * ews.lane<0>()
+ dist1 * dist1 * ews.lane<1>()
+ dist2 * dist2 * ews.lane<2>();
haccumulate(rgbl_errv, error, mask);
// Compute luma error - no "amod", its always zero
param = data_r * l_bs0
+ data_g * l_bs1
+ data_b * l_bs2;
dist0 = (param * l_bs0) - data_r;
dist1 = (param * l_bs1) - data_g;
dist2 = (param * l_bs2) - data_b;
error = dist0 * dist0 * ews.lane<0>()
+ dist1 * dist1 * ews.lane<1>()
+ dist2 * dist2 * ews.lane<2>();
haccumulate(l_errv, error, mask);
}
a_drop_err = hadd_s(a_drop_errv) * ews.lane<3>();
uncor_err = hadd_s(uncor_errv);
samec_err = hadd_s(samec_errv);
rgbl_err = hadd_s(rgbl_errv);
l_err = hadd_s(l_errv);
}
/**
* @brief For a given set of input colors and partitioning determine endpoint encode errors.
*
* This function determines the color error that results from RGB-scale encoding (LDR only),
* RGB-lumashift encoding (HDR only), luminance-encoding, and alpha drop. Also determines whether
* the endpoints are eligible for offset encoding or blue-contraction
*
* @param blk The image block.
* @param pi The partition info data.
* @param ep The idealized endpoints.
* @param[out] eci The resulting encoding choice error metrics.
*/
static void compute_encoding_choice_errors(
const image_block& blk,
const partition_info& pi,
const endpoints& ep,
encoding_choice_errors eci[BLOCK_MAX_PARTITIONS])
{
int partition_count = pi.partition_count;
promise(partition_count > 0);
partition_metrics pms[BLOCK_MAX_PARTITIONS];
compute_avgs_and_dirs_3_comp_rgb(pi, blk, pms);
for (int i = 0; i < partition_count; i++)
{
partition_metrics& pm = pms[i];
line3 uncor_rgb_lines;
line3 samec_rgb_lines; // for LDR-RGB-scale
line3 rgb_luma_lines; // for HDR-RGB-scale
processed_line3 uncor_rgb_plines;
processed_line3 samec_rgb_plines;
processed_line3 rgb_luma_plines;
processed_line3 luminance_plines;
float uncorr_rgb_error;
float samechroma_rgb_error;
float rgb_luma_error;
float luminance_rgb_error;
float alpha_drop_error;
uncor_rgb_lines.a = pm.avg;
uncor_rgb_lines.b = normalize_safe(pm.dir, unit3());
samec_rgb_lines.a = vfloat4::zero();
samec_rgb_lines.b = normalize_safe(pm.avg, unit3());
rgb_luma_lines.a = pm.avg;
rgb_luma_lines.b = unit3();
uncor_rgb_plines.amod = uncor_rgb_lines.a - uncor_rgb_lines.b * dot3(uncor_rgb_lines.a, uncor_rgb_lines.b);
uncor_rgb_plines.bs = uncor_rgb_lines.b;
// Same chroma always goes though zero, so this is simpler than the others
samec_rgb_plines.amod = vfloat4::zero();
samec_rgb_plines.bs = samec_rgb_lines.b;
rgb_luma_plines.amod = rgb_luma_lines.a - rgb_luma_lines.b * dot3(rgb_luma_lines.a, rgb_luma_lines.b);
rgb_luma_plines.bs = rgb_luma_lines.b;
// Luminance always goes though zero, so this is simpler than the others
luminance_plines.amod = vfloat4::zero();
luminance_plines.bs = unit3();
compute_error_squared_rgb_single_partition(
pi, i, blk,
uncor_rgb_plines, uncorr_rgb_error,
samec_rgb_plines, samechroma_rgb_error,
rgb_luma_plines, rgb_luma_error,
luminance_plines, luminance_rgb_error,
alpha_drop_error);
// Determine if we can offset encode RGB lanes
vfloat4 endpt0 = ep.endpt0[i];
vfloat4 endpt1 = ep.endpt1[i];
vfloat4 endpt_diff = abs(endpt1 - endpt0);
vmask4 endpt_can_offset = endpt_diff < vfloat4(0.12f * 65535.0f);
bool can_offset_encode = (mask(endpt_can_offset) & 0x7) == 0x7;
// Store out the settings
eci[i].rgb_scale_error = (samechroma_rgb_error - uncorr_rgb_error) * 0.7f; // empirical
eci[i].rgb_luma_error = (rgb_luma_error - uncorr_rgb_error) * 1.5f; // wild guess
eci[i].luminance_error = (luminance_rgb_error - uncorr_rgb_error) * 3.0f; // empirical
eci[i].alpha_drop_error = alpha_drop_error * 3.0f;
eci[i].can_offset_encode = can_offset_encode;
eci[i].can_blue_contract = !blk.is_luminance();
}
}
/**
* @brief For a given partition compute the error for every endpoint integer count and quant level.
*
* @param encode_hdr_rgb @c true if using HDR for RGB, @c false for LDR.
* @param encode_hdr_alpha @c true if using HDR for alpha, @c false for LDR.
* @param partition_index The partition index.
* @param pi The partition info.
* @param eci The encoding choice error metrics.
* @param ep The idealized endpoints.
* @param error_weight The resulting encoding choice error metrics.
* @param[out] best_error The best error for each integer count and quant level.
* @param[out] format_of_choice The preferred endpoint format for each integer count and quant level.
*/
static void compute_color_error_for_every_integer_count_and_quant_level(
bool encode_hdr_rgb,
bool encode_hdr_alpha,
int partition_index,
const partition_info& pi,
const encoding_choice_errors& eci,
const endpoints& ep,
vfloat4 error_weight,
float best_error[21][4],
uint8_t format_of_choice[21][4]
) {
int partition_size = pi.partition_texel_count[partition_index];
static const float baseline_quant_error[21 - QUANT_6] {
(65536.0f * 65536.0f / 18.0f) / (5 * 5),
(65536.0f * 65536.0f / 18.0f) / (7 * 7),
(65536.0f * 65536.0f / 18.0f) / (9 * 9),
(65536.0f * 65536.0f / 18.0f) / (11 * 11),
(65536.0f * 65536.0f / 18.0f) / (15 * 15),
(65536.0f * 65536.0f / 18.0f) / (19 * 19),
(65536.0f * 65536.0f / 18.0f) / (23 * 23),
(65536.0f * 65536.0f / 18.0f) / (31 * 31),
(65536.0f * 65536.0f / 18.0f) / (39 * 39),
(65536.0f * 65536.0f / 18.0f) / (47 * 47),
(65536.0f * 65536.0f / 18.0f) / (63 * 63),
(65536.0f * 65536.0f / 18.0f) / (79 * 79),
(65536.0f * 65536.0f / 18.0f) / (95 * 95),
(65536.0f * 65536.0f / 18.0f) / (127 * 127),
(65536.0f * 65536.0f / 18.0f) / (159 * 159),
(65536.0f * 65536.0f / 18.0f) / (191 * 191),
(65536.0f * 65536.0f / 18.0f) / (255 * 255)
};
vfloat4 ep0 = ep.endpt0[partition_index];
vfloat4 ep1 = ep.endpt1[partition_index];
float ep1_min = hmin_rgb_s(ep1);
ep1_min = astc::max(ep1_min, 0.0f);
float error_weight_rgbsum = hadd_rgb_s(error_weight);
float range_upper_limit_rgb = encode_hdr_rgb ? 61440.0f : 65535.0f;
float range_upper_limit_alpha = encode_hdr_alpha ? 61440.0f : 65535.0f;
// It is possible to get endpoint colors significantly outside [0,upper-limit] even if the
// input data are safely contained in [0,upper-limit]; we need to add an error term for this
vfloat4 offset(range_upper_limit_rgb, range_upper_limit_rgb, range_upper_limit_rgb, range_upper_limit_alpha);
vfloat4 ep0_range_error_high = max(ep0 - offset, 0.0f);
vfloat4 ep1_range_error_high = max(ep1 - offset, 0.0f);
vfloat4 ep0_range_error_low = min(ep0, 0.0f);
vfloat4 ep1_range_error_low = min(ep1, 0.0f);
vfloat4 sum_range_error =
(ep0_range_error_low * ep0_range_error_low) +
(ep1_range_error_low * ep1_range_error_low) +
(ep0_range_error_high * ep0_range_error_high) +
(ep1_range_error_high * ep1_range_error_high);
float rgb_range_error = dot3_s(sum_range_error, error_weight)
* 0.5f * static_cast<float>(partition_size);
float alpha_range_error = sum_range_error.lane<3>() * error_weight.lane<3>()
* 0.5f * static_cast<float>(partition_size);
if (encode_hdr_rgb)
{
// Collect some statistics
float af, cf;
if (ep1.lane<0>() > ep1.lane<1>() && ep1.lane<0>() > ep1.lane<2>())
{
af = ep1.lane<0>();
cf = ep1.lane<0>() - ep0.lane<0>();
}
else if (ep1.lane<1>() > ep1.lane<2>())
{
af = ep1.lane<1>();
cf = ep1.lane<1>() - ep0.lane<1>();
}
else
{
af = ep1.lane<2>();
cf = ep1.lane<2>() - ep0.lane<2>();
}
// Estimate of color-component spread in high endpoint color
float bf = af - ep1_min;
vfloat4 prd = (ep1 - vfloat4(cf)).swz<0, 1, 2>();
vfloat4 pdif = prd - ep0.swz<0, 1, 2>();
// Estimate of color-component spread in low endpoint color
float df = hmax_s(abs(pdif));
int b = static_cast<int>(bf);
int c = static_cast<int>(cf);
int d = static_cast<int>(df);
// Determine which one of the 6 submodes is likely to be used in case of an RGBO-mode
int rgbo_mode = 5; // 7 bits per component
// mode 4: 8 7 6
if (b < 32768 && c < 16384)
{
rgbo_mode = 4;
}
// mode 3: 9 6 7
if (b < 8192 && c < 16384)
{
rgbo_mode = 3;
}
// mode 2: 10 5 8
if (b < 2048 && c < 16384)
{
rgbo_mode = 2;
}
// mode 1: 11 6 5
if (b < 2048 && c < 1024)
{
rgbo_mode = 1;
}
// mode 0: 11 5 7
if (b < 1024 && c < 4096)
{
rgbo_mode = 0;
}
// Determine which one of the 9 submodes is likely to be used in case of an RGB-mode.
int rgb_mode = 8; // 8 bits per component, except 7 bits for blue
// mode 0: 9 7 6 7
if (b < 16384 && c < 8192 && d < 8192)
{
rgb_mode = 0;
}
// mode 1: 9 8 6 6
if (b < 32768 && c < 8192 && d < 4096)
{
rgb_mode = 1;
}
// mode 2: 10 6 7 7
if (b < 4096 && c < 8192 && d < 4096)
{
rgb_mode = 2;
}
// mode 3: 10 7 7 6
if (b < 8192 && c < 8192 && d < 2048)
{
rgb_mode = 3;
}
// mode 4: 11 8 6 5
if (b < 8192 && c < 2048 && d < 512)
{
rgb_mode = 4;
}
// mode 5: 11 6 8 6
if (b < 2048 && c < 8192 && d < 1024)
{
rgb_mode = 5;
}
// mode 6: 12 7 7 5
if (b < 2048 && c < 2048 && d < 256)
{
rgb_mode = 6;
}
// mode 7: 12 6 7 6
if (b < 1024 && c < 2048 && d < 512)
{
rgb_mode = 7;
}
static const float rgbo_error_scales[6] { 4.0f, 4.0f, 16.0f, 64.0f, 256.0f, 1024.0f };
static const float rgb_error_scales[9] { 64.0f, 64.0f, 16.0f, 16.0f, 4.0f, 4.0f, 1.0f, 1.0f, 384.0f };
float mode7mult = rgbo_error_scales[rgbo_mode] * 0.0015f; // Empirically determined ....
float mode11mult = rgb_error_scales[rgb_mode] * 0.010f; // Empirically determined ....
float lum_high = hadd_rgb_s(ep1) * (1.0f / 3.0f);
float lum_low = hadd_rgb_s(ep0) * (1.0f / 3.0f);
float lumdif = lum_high - lum_low;
float mode23mult = lumdif < 960 ? 4.0f : lumdif < 3968 ? 16.0f : 128.0f;
mode23mult *= 0.0005f; // Empirically determined ....
// Pick among the available HDR endpoint modes
for (int i = QUANT_2; i < QUANT_16; i++)
{
best_error[i][3] = ERROR_CALC_DEFAULT;
best_error[i][2] = ERROR_CALC_DEFAULT;
best_error[i][1] = ERROR_CALC_DEFAULT;
best_error[i][0] = ERROR_CALC_DEFAULT;
format_of_choice[i][3] = static_cast<uint8_t>(encode_hdr_alpha ? FMT_HDR_RGBA : FMT_HDR_RGB_LDR_ALPHA);
format_of_choice[i][2] = FMT_HDR_RGB;
format_of_choice[i][1] = FMT_HDR_RGB_SCALE;
format_of_choice[i][0] = FMT_HDR_LUMINANCE_LARGE_RANGE;
}
for (int i = QUANT_16; i <= QUANT_256; i++)
{
// The base_quant_error should depend on the scale-factor that would be used during
// actual encode of the color value
float base_quant_error = baseline_quant_error[i - QUANT_6] * static_cast<float>(partition_size);
float rgb_quantization_error = error_weight_rgbsum * base_quant_error * 2.0f;
float alpha_quantization_error = error_weight.lane<3>() * base_quant_error * 2.0f;
float rgba_quantization_error = rgb_quantization_error + alpha_quantization_error;
// For 8 integers, we have two encodings: one with HDR A and another one with LDR A
float full_hdr_rgba_error = rgba_quantization_error + rgb_range_error + alpha_range_error;
best_error[i][3] = full_hdr_rgba_error;
format_of_choice[i][3] = static_cast<uint8_t>(encode_hdr_alpha ? FMT_HDR_RGBA : FMT_HDR_RGB_LDR_ALPHA);
// For 6 integers, we have one HDR-RGB encoding
float full_hdr_rgb_error = (rgb_quantization_error * mode11mult) + rgb_range_error + eci.alpha_drop_error;
best_error[i][2] = full_hdr_rgb_error;
format_of_choice[i][2] = FMT_HDR_RGB;
// For 4 integers, we have one HDR-RGB-Scale encoding
float hdr_rgb_scale_error = (rgb_quantization_error * mode7mult) + rgb_range_error + eci.alpha_drop_error + eci.rgb_luma_error;
best_error[i][1] = hdr_rgb_scale_error;
format_of_choice[i][1] = FMT_HDR_RGB_SCALE;
// For 2 integers, we assume luminance-with-large-range
float hdr_luminance_error = (rgb_quantization_error * mode23mult) + rgb_range_error + eci.alpha_drop_error + eci.luminance_error;
best_error[i][0] = hdr_luminance_error;
format_of_choice[i][0] = FMT_HDR_LUMINANCE_LARGE_RANGE;
}
}
else
{
for (int i = QUANT_2; i < QUANT_6; i++)
{
best_error[i][3] = ERROR_CALC_DEFAULT;
best_error[i][2] = ERROR_CALC_DEFAULT;
best_error[i][1] = ERROR_CALC_DEFAULT;
best_error[i][0] = ERROR_CALC_DEFAULT;
format_of_choice[i][3] = FMT_RGBA;
format_of_choice[i][2] = FMT_RGB;
format_of_choice[i][1] = FMT_RGB_SCALE;
format_of_choice[i][0] = FMT_LUMINANCE;
}
float base_quant_error_rgb = error_weight_rgbsum * static_cast<float>(partition_size);
float base_quant_error_a = error_weight.lane<3>() * static_cast<float>(partition_size);
float base_quant_error_rgba = base_quant_error_rgb + base_quant_error_a;
float error_scale_bc_rgba = eci.can_blue_contract ? 0.625f : 1.0f;
float error_scale_oe_rgba = eci.can_offset_encode ? 0.5f : 1.0f;
float error_scale_bc_rgb = eci.can_blue_contract ? 0.5f : 1.0f;
float error_scale_oe_rgb = eci.can_offset_encode ? 0.25f : 1.0f;
// Pick among the available LDR endpoint modes
for (int i = QUANT_6; i <= QUANT_256; i++)
{
// Offset encoding not possible at higher quant levels
if (i >= QUANT_192)
{
error_scale_oe_rgba = 1.0f;
error_scale_oe_rgb = 1.0f;
}
float base_quant_error = baseline_quant_error[i - QUANT_6];
float quant_error_rgb = base_quant_error_rgb * base_quant_error;
float quant_error_rgba = base_quant_error_rgba * base_quant_error;
// 8 integers can encode as RGBA+RGBA
float full_ldr_rgba_error = quant_error_rgba
* error_scale_bc_rgba
* error_scale_oe_rgba
+ rgb_range_error
+ alpha_range_error;
best_error[i][3] = full_ldr_rgba_error;
format_of_choice[i][3] = FMT_RGBA;
// 6 integers can encode as RGB+RGB or RGBS+AA
float full_ldr_rgb_error = quant_error_rgb
* error_scale_bc_rgb
* error_scale_oe_rgb
+ rgb_range_error
+ eci.alpha_drop_error;
float rgbs_alpha_error = quant_error_rgba
+ eci.rgb_scale_error
+ rgb_range_error
+ alpha_range_error;
if (rgbs_alpha_error < full_ldr_rgb_error)
{
best_error[i][2] = rgbs_alpha_error;
format_of_choice[i][2] = FMT_RGB_SCALE_ALPHA;
}
else
{
best_error[i][2] = full_ldr_rgb_error;
format_of_choice[i][2] = FMT_RGB;
}
// 4 integers can encode as RGBS or LA+LA
float ldr_rgbs_error = quant_error_rgb
+ rgb_range_error
+ eci.alpha_drop_error
+ eci.rgb_scale_error;
float lum_alpha_error = quant_error_rgba
+ rgb_range_error
+ alpha_range_error
+ eci.luminance_error;
if (ldr_rgbs_error < lum_alpha_error)
{
best_error[i][1] = ldr_rgbs_error;
format_of_choice[i][1] = FMT_RGB_SCALE;
}
else
{
best_error[i][1] = lum_alpha_error;
format_of_choice[i][1] = FMT_LUMINANCE_ALPHA;
}
// 2 integers can encode as L+L
float luminance_error = quant_error_rgb
+ rgb_range_error
+ eci.alpha_drop_error
+ eci.luminance_error;
best_error[i][0] = luminance_error;
format_of_choice[i][0] = FMT_LUMINANCE;
}
}
}
/**
* @brief For one partition compute the best format and quantization for a given bit count.
*
* @param best_combined_error The best error for each quant level and integer count.
* @param best_combined_format The best format for each quant level and integer count.
* @param bits_available The number of bits available for encoding.
* @param[out] best_quant_level The output best color quant level.
* @param[out] best_format The output best color format.
*
* @return The output error for the best pairing.
*/
static float one_partition_find_best_combination_for_bitcount(
const float best_combined_error[21][4],
const uint8_t best_combined_format[21][4],
int bits_available,
uint8_t& best_quant_level,
uint8_t& best_format
) {
int best_integer_count = 0;
float best_integer_count_error = ERROR_CALC_DEFAULT;
for (int integer_count = 1; integer_count <= 4; integer_count++)
{
// Compute the quantization level for a given number of integers and a given number of bits
int quant_level = quant_mode_table[integer_count][bits_available];
// Don't have enough bits to represent a given endpoint format at all!
if (quant_level < QUANT_6)
{
continue;
}
float integer_count_error = best_combined_error[quant_level][integer_count - 1];
if (integer_count_error < best_integer_count_error)
{
best_integer_count_error = integer_count_error;
best_integer_count = integer_count - 1;
}
}
int ql = quant_mode_table[best_integer_count + 1][bits_available];
best_quant_level = static_cast<uint8_t>(ql);
best_format = FMT_LUMINANCE;
if (ql >= QUANT_6)
{
best_format = best_combined_format[ql][best_integer_count];
}
return best_integer_count_error;
}
/**
* @brief For 2 partitions compute the best format combinations for every pair of quant mode and integer count.
*
* @param best_error The best error for a single endpoint quant level and integer count.
* @param best_format The best format for a single endpoint quant level and integer count.
* @param[out] best_combined_error The best combined error pairings for the 2 partitions.
* @param[out] best_combined_format The best combined format pairings for the 2 partitions.
*/
static void two_partitions_find_best_combination_for_every_quantization_and_integer_count(
const float best_error[2][21][4], // indexed by (partition, quant-level, integer-pair-count-minus-1)
const uint8_t best_format[2][21][4],
float best_combined_error[21][7], // indexed by (quant-level, integer-pair-count-minus-2)
uint8_t best_combined_format[21][7][2]
) {
for (int i = QUANT_2; i <= QUANT_256; i++)
{
for (int j = 0; j < 7; j++)
{
best_combined_error[i][j] = ERROR_CALC_DEFAULT;
}
}
for (int quant = QUANT_6; quant <= QUANT_256; quant++)
{
for (int i = 0; i < 4; i++) // integer-count for first endpoint-pair
{
for (int j = 0; j < 4; j++) // integer-count for second endpoint-pair
{
int low2 = astc::min(i, j);
int high2 = astc::max(i, j);
if ((high2 - low2) > 1)
{
continue;
}
int intcnt = i + j;
float errorterm = astc::min(best_error[0][quant][i] + best_error[1][quant][j], 1e10f);
if (errorterm <= best_combined_error[quant][intcnt])
{
best_combined_error[quant][intcnt] = errorterm;
best_combined_format[quant][intcnt][0] = best_format[0][quant][i];
best_combined_format[quant][intcnt][1] = best_format[1][quant][j];
}
}
}
}
}
/**
* @brief For 2 partitions compute the best format and quantization for a given bit count.
*
* @param best_combined_error The best error for each quant level and integer count.
* @param best_combined_format The best format for each quant level and integer count.
* @param bits_available The number of bits available for encoding.
* @param[out] best_quant_level The output best color quant level.
* @param[out] best_quant_level_mod The output best color quant level assuming two more bits are available.
* @param[out] best_formats The output best color formats.
*
* @return The output error for the best pairing.
*/
static float two_partitions_find_best_combination_for_bitcount(
float best_combined_error[21][7],
uint8_t best_combined_format[21][7][2],
int bits_available,
uint8_t& best_quant_level,
uint8_t& best_quant_level_mod,
uint8_t* best_formats
) {
int best_integer_count = 0;
float best_integer_count_error = ERROR_CALC_DEFAULT;
for (int integer_count = 2; integer_count <= 8; integer_count++)
{
// Compute the quantization level for a given number of integers and a given number of bits
int quant_level = quant_mode_table[integer_count][bits_available];
// Don't have enough bits to represent a given endpoint format at all!
if (quant_level < QUANT_6)
{
break;
}
float integer_count_error = best_combined_error[quant_level][integer_count - 2];
if (integer_count_error < best_integer_count_error)
{
best_integer_count_error = integer_count_error;
best_integer_count = integer_count;
}
}
int ql = quant_mode_table[best_integer_count][bits_available];
int ql_mod = quant_mode_table[best_integer_count][bits_available + 2];
best_quant_level = static_cast<uint8_t>(ql);
best_quant_level_mod = static_cast<uint8_t>(ql_mod);
if (ql >= QUANT_6)
{
for (int i = 0; i < 2; i++)
{
best_formats[i] = best_combined_format[ql][best_integer_count - 2][i];
}
}
else
{
for (int i = 0; i < 2; i++)
{
best_formats[i] = FMT_LUMINANCE;
}
}
return best_integer_count_error;
}
/**
* @brief For 3 partitions compute the best format combinations for every pair of quant mode and integer count.
*
* @param best_error The best error for a single endpoint quant level and integer count.
* @param best_format The best format for a single endpoint quant level and integer count.
* @param[out] best_combined_error The best combined error pairings for the 3 partitions.
* @param[out] best_combined_format The best combined format pairings for the 3 partitions.
*/
static void three_partitions_find_best_combination_for_every_quantization_and_integer_count(
const float best_error[3][21][4], // indexed by (partition, quant-level, integer-count)
const uint8_t best_format[3][21][4],
float best_combined_error[21][10],
uint8_t best_combined_format[21][10][3]
) {
for (int i = QUANT_2; i <= QUANT_256; i++)
{
for (int j = 0; j < 10; j++)
{
best_combined_error[i][j] = ERROR_CALC_DEFAULT;
}
}
for (int quant = QUANT_6; quant <= QUANT_256; quant++)
{
for (int i = 0; i < 4; i++) // integer-count for first endpoint-pair
{
for (int j = 0; j < 4; j++) // integer-count for second endpoint-pair
{
int low2 = astc::min(i, j);
int high2 = astc::max(i, j);
if ((high2 - low2) > 1)
{
continue;
}
for (int k = 0; k < 4; k++) // integer-count for third endpoint-pair
{
int low3 = astc::min(k, low2);
int high3 = astc::max(k, high2);
if ((high3 - low3) > 1)
{
continue;
}
int intcnt = i + j + k;
float errorterm = astc::min(best_error[0][quant][i] + best_error[1][quant][j] + best_error[2][quant][k], 1e10f);
if (errorterm <= best_combined_error[quant][intcnt])
{
best_combined_error[quant][intcnt] = errorterm;
best_combined_format[quant][intcnt][0] = best_format[0][quant][i];
best_combined_format[quant][intcnt][1] = best_format[1][quant][j];
best_combined_format[quant][intcnt][2] = best_format[2][quant][k];
}
}
}
}
}
}
/**
* @brief For 3 partitions compute the best format and quantization for a given bit count.
*
* @param best_combined_error The best error for each quant level and integer count.
* @param best_combined_format The best format for each quant level and integer count.
* @param bits_available The number of bits available for encoding.
* @param[out] best_quant_level The output best color quant level.
* @param[out] best_quant_level_mod The output best color quant level assuming two more bits are available.
* @param[out] best_formats The output best color formats.
*
* @return The output error for the best pairing.
*/
static float three_partitions_find_best_combination_for_bitcount(
const float best_combined_error[21][10],
const uint8_t best_combined_format[21][10][3],
int bits_available,
uint8_t& best_quant_level,
uint8_t& best_quant_level_mod,
uint8_t* best_formats
) {
int best_integer_count = 0;
float best_integer_count_error = ERROR_CALC_DEFAULT;
for (int integer_count = 3; integer_count <= 9; integer_count++)
{
// Compute the quantization level for a given number of integers and a given number of bits
int quant_level = quant_mode_table[integer_count][bits_available];
// Don't have enough bits to represent a given endpoint format at all!
if (quant_level < QUANT_6)
{
break;
}
float integer_count_error = best_combined_error[quant_level][integer_count - 3];
if (integer_count_error < best_integer_count_error)
{
best_integer_count_error = integer_count_error;
best_integer_count = integer_count;
}
}
int ql = quant_mode_table[best_integer_count][bits_available];
int ql_mod = quant_mode_table[best_integer_count][bits_available + 5];
best_quant_level = static_cast<uint8_t>(ql);
best_quant_level_mod = static_cast<uint8_t>(ql_mod);
if (ql >= QUANT_6)
{
for (int i = 0; i < 3; i++)
{
best_formats[i] = best_combined_format[ql][best_integer_count - 3][i];
}
}
else
{
for (int i = 0; i < 3; i++)
{
best_formats[i] = FMT_LUMINANCE;
}
}
return best_integer_count_error;
}
/**
* @brief For 4 partitions compute the best format combinations for every pair of quant mode and integer count.
*
* @param best_error The best error for a single endpoint quant level and integer count.
* @param best_format The best format for a single endpoint quant level and integer count.
* @param[out] best_combined_error The best combined error pairings for the 4 partitions.
* @param[out] best_combined_format The best combined format pairings for the 4 partitions.
*/
static void four_partitions_find_best_combination_for_every_quantization_and_integer_count(
const float best_error[4][21][4], // indexed by (partition, quant-level, integer-count)
const uint8_t best_format[4][21][4],
float best_combined_error[21][13],
uint8_t best_combined_format[21][13][4]
) {
for (int i = QUANT_2; i <= QUANT_256; i++)
{
for (int j = 0; j < 13; j++)
{
best_combined_error[i][j] = ERROR_CALC_DEFAULT;
}
}
for (int quant = QUANT_6; quant <= QUANT_256; quant++)
{
for (int i = 0; i < 4; i++) // integer-count for first endpoint-pair
{
for (int j = 0; j < 4; j++) // integer-count for second endpoint-pair
{
int low2 = astc::min(i, j);
int high2 = astc::max(i, j);
if ((high2 - low2) > 1)
{
continue;
}
for (int k = 0; k < 4; k++) // integer-count for third endpoint-pair
{
int low3 = astc::min(k, low2);
int high3 = astc::max(k, high2);
if ((high3 - low3) > 1)
{
continue;
}
for (int l = 0; l < 4; l++) // integer-count for fourth endpoint-pair
{
int low4 = astc::min(l, low3);
int high4 = astc::max(l, high3);
if ((high4 - low4) > 1)
{
continue;
}
int intcnt = i + j + k + l;
float errorterm = astc::min(best_error[0][quant][i] + best_error[1][quant][j] + best_error[2][quant][k] + best_error[3][quant][l], 1e10f);
if (errorterm <= best_combined_error[quant][intcnt])
{
best_combined_error[quant][intcnt] = errorterm;
best_combined_format[quant][intcnt][0] = best_format[0][quant][i];
best_combined_format[quant][intcnt][1] = best_format[1][quant][j];
best_combined_format[quant][intcnt][2] = best_format[2][quant][k];
best_combined_format[quant][intcnt][3] = best_format[3][quant][l];
}
}
}
}
}
}
}
/**
* @brief For 4 partitions compute the best format and quantization for a given bit count.
*
* @param best_combined_error The best error for each quant level and integer count.
* @param best_combined_format The best format for each quant level and integer count.
* @param bits_available The number of bits available for encoding.
* @param[out] best_quant_level The output best color quant level.
* @param[out] best_quant_level_mod The output best color quant level assuming two more bits are available.
* @param[out] best_formats The output best color formats.
*
* @return best_error The output error for the best pairing.
*/
static float four_partitions_find_best_combination_for_bitcount(
const float best_combined_error[21][13],
const uint8_t best_combined_format[21][13][4],
int bits_available,
uint8_t& best_quant_level,
uint8_t& best_quant_level_mod,
uint8_t* best_formats
) {
int best_integer_count = 0;
float best_integer_count_error = ERROR_CALC_DEFAULT;
for (int integer_count = 4; integer_count <= 9; integer_count++)
{
// Compute the quantization level for a given number of integers and a given number of bits
int quant_level = quant_mode_table[integer_count][bits_available];
// Don't have enough bits to represent a given endpoint format at all!
if (quant_level < QUANT_6)
{
break;
}
float integer_count_error = best_combined_error[quant_level][integer_count - 4];
if (integer_count_error < best_integer_count_error)
{
best_integer_count_error = integer_count_error;
best_integer_count = integer_count;
}
}
int ql = quant_mode_table[best_integer_count][bits_available];
int ql_mod = quant_mode_table[best_integer_count][bits_available + 8];
best_quant_level = static_cast<uint8_t>(ql);
best_quant_level_mod = static_cast<uint8_t>(ql_mod);
if (ql >= QUANT_6)
{
for (int i = 0; i < 4; i++)
{
best_formats[i] = best_combined_format[ql][best_integer_count - 4][i];
}
}
else
{
for (int i = 0; i < 4; i++)
{
best_formats[i] = FMT_LUMINANCE;
}
}
return best_integer_count_error;
}
/* See header for documentation. */
unsigned int compute_ideal_endpoint_formats(
const partition_info& pi,
const image_block& blk,
const endpoints& ep,
// bitcounts and errors computed for the various quantization methods
const int8_t* qwt_bitcounts,
const float* qwt_errors,
unsigned int tune_candidate_limit,
unsigned int start_block_mode,
unsigned int end_block_mode,
// output data
uint8_t partition_format_specifiers[TUNE_MAX_TRIAL_CANDIDATES][BLOCK_MAX_PARTITIONS],
int block_mode[TUNE_MAX_TRIAL_CANDIDATES],
quant_method quant_level[TUNE_MAX_TRIAL_CANDIDATES],
quant_method quant_level_mod[TUNE_MAX_TRIAL_CANDIDATES],
compression_working_buffers& tmpbuf
) {
int partition_count = pi.partition_count;
promise(partition_count > 0);
bool encode_hdr_rgb = static_cast<bool>(blk.rgb_lns[0]);
bool encode_hdr_alpha = static_cast<bool>(blk.alpha_lns[0]);
// Compute the errors that result from various encoding choices (such as using luminance instead
// of RGB, discarding Alpha, using RGB-scale in place of two separate RGB endpoints and so on)
encoding_choice_errors eci[BLOCK_MAX_PARTITIONS];
compute_encoding_choice_errors(blk, pi, ep, eci);
float best_error[BLOCK_MAX_PARTITIONS][21][4];
uint8_t format_of_choice[BLOCK_MAX_PARTITIONS][21][4];
for (int i = 0; i < partition_count; i++)
{
compute_color_error_for_every_integer_count_and_quant_level(
encode_hdr_rgb, encode_hdr_alpha, i,
pi, eci[i], ep, blk.channel_weight, best_error[i],
format_of_choice[i]);
}
float* errors_of_best_combination = tmpbuf.errors_of_best_combination;
uint8_t* best_quant_levels = tmpbuf.best_quant_levels;
uint8_t* best_quant_levels_mod = tmpbuf.best_quant_levels_mod;
uint8_t (&best_ep_formats)[WEIGHTS_MAX_BLOCK_MODES][BLOCK_MAX_PARTITIONS] = tmpbuf.best_ep_formats;
// Ensure that the first iteration understep contains data that will never be picked
vfloat clear_error(ERROR_CALC_DEFAULT);
vint clear_quant(0);
unsigned int packed_start_block_mode = round_down_to_simd_multiple_vla(start_block_mode);
storea(clear_error, errors_of_best_combination + packed_start_block_mode);
store_nbytes(clear_quant, best_quant_levels + packed_start_block_mode);
store_nbytes(clear_quant, best_quant_levels_mod + packed_start_block_mode);
// Ensure that last iteration overstep contains data that will never be picked
unsigned int packed_end_block_mode = round_down_to_simd_multiple_vla(end_block_mode - 1);
storea(clear_error, errors_of_best_combination + packed_end_block_mode);
store_nbytes(clear_quant, best_quant_levels + packed_end_block_mode);
store_nbytes(clear_quant, best_quant_levels_mod + packed_end_block_mode);
// Track a scalar best to avoid expensive search at least once ...
float error_of_best_combination = ERROR_CALC_DEFAULT;
int index_of_best_combination = -1;
// The block contains 1 partition
if (partition_count == 1)
{
for (unsigned int i = start_block_mode; i < end_block_mode; i++)
{
if (qwt_errors[i] >= ERROR_CALC_DEFAULT)
{
errors_of_best_combination[i] = ERROR_CALC_DEFAULT;
continue;
}
float error_of_best = one_partition_find_best_combination_for_bitcount(
best_error[0], format_of_choice[0], qwt_bitcounts[i],
best_quant_levels[i], best_ep_formats[i][0]);
float total_error = error_of_best + qwt_errors[i];
errors_of_best_combination[i] = total_error;
best_quant_levels_mod[i] = best_quant_levels[i];
if (total_error < error_of_best_combination)
{
error_of_best_combination = total_error;
index_of_best_combination = i;
}
}
}
// The block contains 2 partitions
else if (partition_count == 2)
{
float combined_best_error[21][7];
uint8_t formats_of_choice[21][7][2];
two_partitions_find_best_combination_for_every_quantization_and_integer_count(
best_error, format_of_choice, combined_best_error, formats_of_choice);
assert(start_block_mode == 0);
for (unsigned int i = 0; i < end_block_mode; i++)
{
if (qwt_errors[i] >= ERROR_CALC_DEFAULT)
{
errors_of_best_combination[i] = ERROR_CALC_DEFAULT;
continue;
}
float error_of_best = two_partitions_find_best_combination_for_bitcount(
combined_best_error, formats_of_choice, qwt_bitcounts[i],
best_quant_levels[i], best_quant_levels_mod[i],
best_ep_formats[i]);
float total_error = error_of_best + qwt_errors[i];
errors_of_best_combination[i] = total_error;
if (total_error < error_of_best_combination)
{
error_of_best_combination = total_error;
index_of_best_combination = i;
}
}
}
// The block contains 3 partitions
else if (partition_count == 3)
{
float combined_best_error[21][10];
uint8_t formats_of_choice[21][10][3];
three_partitions_find_best_combination_for_every_quantization_and_integer_count(
best_error, format_of_choice, combined_best_error, formats_of_choice);
assert(start_block_mode == 0);
for (unsigned int i = 0; i < end_block_mode; i++)
{
if (qwt_errors[i] >= ERROR_CALC_DEFAULT)
{
errors_of_best_combination[i] = ERROR_CALC_DEFAULT;
continue;
}
float error_of_best = three_partitions_find_best_combination_for_bitcount(
combined_best_error, formats_of_choice, qwt_bitcounts[i],
best_quant_levels[i], best_quant_levels_mod[i],
best_ep_formats[i]);
float total_error = error_of_best + qwt_errors[i];
errors_of_best_combination[i] = total_error;
if (total_error < error_of_best_combination)
{
error_of_best_combination = total_error;
index_of_best_combination = i;
}
}
}
// The block contains 4 partitions
else // if (partition_count == 4)
{
assert(partition_count == 4);
float combined_best_error[21][13];
uint8_t formats_of_choice[21][13][4];
four_partitions_find_best_combination_for_every_quantization_and_integer_count(
best_error, format_of_choice, combined_best_error, formats_of_choice);
assert(start_block_mode == 0);
for (unsigned int i = 0; i < end_block_mode; i++)
{
if (qwt_errors[i] >= ERROR_CALC_DEFAULT)
{
errors_of_best_combination[i] = ERROR_CALC_DEFAULT;
continue;
}
float error_of_best = four_partitions_find_best_combination_for_bitcount(
combined_best_error, formats_of_choice, qwt_bitcounts[i],
best_quant_levels[i], best_quant_levels_mod[i],
best_ep_formats[i]);
float total_error = error_of_best + qwt_errors[i];
errors_of_best_combination[i] = total_error;
if (total_error < error_of_best_combination)
{
error_of_best_combination = total_error;
index_of_best_combination = i;
}
}
}
int best_error_weights[TUNE_MAX_TRIAL_CANDIDATES];
// Fast path the first result and avoid the list search for trial 0
best_error_weights[0] = index_of_best_combination;
if (index_of_best_combination >= 0)
{
errors_of_best_combination[index_of_best_combination] = ERROR_CALC_DEFAULT;
}
// Search the remaining results and pick the best candidate modes for trial 1+
for (unsigned int i = 1; i < tune_candidate_limit; i++)
{
vint vbest_error_index(-1);
vfloat vbest_ep_error(ERROR_CALC_DEFAULT);
start_block_mode = round_down_to_simd_multiple_vla(start_block_mode);
vint lane_ids = vint::lane_id() + vint(start_block_mode);
for (unsigned int j = start_block_mode; j < end_block_mode; j += ASTCENC_SIMD_WIDTH)
{
vfloat err = vfloat(errors_of_best_combination + j);
vmask mask = err < vbest_ep_error;
vbest_ep_error = select(vbest_ep_error, err, mask);
vbest_error_index = select(vbest_error_index, lane_ids, mask);
lane_ids += vint(ASTCENC_SIMD_WIDTH);
}
// Pick best mode from the SIMD result, using lowest matching index to ensure invariance
vmask lanes_min_error = vbest_ep_error == hmin(vbest_ep_error);
vbest_error_index = select(vint(0x7FFFFFFF), vbest_error_index, lanes_min_error);
vbest_error_index = hmin(vbest_error_index);
int best_error_index = vbest_error_index.lane<0>();
best_error_weights[i] = best_error_index;
// Max the error for this candidate so we don't pick it again
if (best_error_index >= 0)
{
errors_of_best_combination[best_error_index] = ERROR_CALC_DEFAULT;
}
// Early-out if no more candidates are valid
else
{
break;
}
}
for (unsigned int i = 0; i < tune_candidate_limit; i++)
{
if (best_error_weights[i] < 0)
{
return i;
}
block_mode[i] = best_error_weights[i];
quant_level[i] = static_cast<quant_method>(best_quant_levels[best_error_weights[i]]);
quant_level_mod[i] = static_cast<quant_method>(best_quant_levels_mod[best_error_weights[i]]);
assert(quant_level[i] >= QUANT_6 && quant_level[i] <= QUANT_256);
assert(quant_level_mod[i] >= QUANT_6 && quant_level_mod[i] <= QUANT_256);
for (int j = 0; j < partition_count; j++)
{
partition_format_specifiers[i][j] = best_ep_formats[best_error_weights[i]][j];
}
}
return tune_candidate_limit;
}
#endif