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quicktex/quicktex/s3tc/bc1/BC1Encoder.cpp

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/* Python-rgbcx Texture Compression Library
Copyright (C) 2021 Andrew Cassidy <drewcassidy@me.com>
Partially derived from rgbcx.h written by Richard Geldreich <richgel99@gmail.com>
and licenced under the public domain
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "BC1Encoder.h"
#include <algorithm>
#include <array>
#include <atomic>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <memory>
#include <stdexcept>
#include <type_traits>
#include "../../Block.h"
#include "../../Color.h"
#include "../../Matrix4x4.h"
#include "../../Texture.h"
#include "../../Vector4.h"
#include "../../Vector4Int.h"
#include "../../bitwiseEnums.h"
#include "../../util.h"
#include "Histogram.h"
#include "OrderTable.h"
#include "SingleColorTable.h"
namespace quicktex::s3tc {
using CBlock = ColorBlock<4, 4>;
using BlockMetrics = CBlock::Metrics;
// constructors
BC1Encoder::BC1Encoder(unsigned int level, ColorMode color_mode, InterpolatorPtr interpolator) : _interpolator(interpolator), _color_mode(color_mode) {
if (color_mode != ColorMode::FourColor && color_mode != ColorMode::ThreeColor && color_mode != ColorMode::ThreeColorBlack) {
throw std::invalid_argument("Encoder color mode must be FourColor, ThreeColor, or ThreeColorBlack");
}
OrderTable<4>::Generate();
_single_match5 = SingleColorTable<5, 4>(_interpolator);
_single_match6 = SingleColorTable<6, 4>(_interpolator);
if (!OrderTable<4>::generated) throw std::runtime_error("Failed to generate 4-color order tables");
if (!_single_match5) throw std::runtime_error("Failed to generate 5-bit 4-color single color table");
if (!_single_match6) throw std::runtime_error("Failed to generate 6-bit 4-color single color table");
if (color_mode != ColorMode::FourColor) {
OrderTable<3>::Generate();
_single_match5_half = SingleColorTable<5, 3>(_interpolator);
_single_match6_half = SingleColorTable<6, 3>(_interpolator);
if (!OrderTable<3>::generated) throw std::runtime_error("Failed to generate 3-color order tables");
if (!_single_match5_half) throw std::runtime_error("Failed to generate 5-bit 3-color single color table");
if (!_single_match6_half) throw std::runtime_error("Failed to generate 6-bit 3-color single color table");
}
SetLevel(level);
}
// Getters and Setters
void BC1Encoder::SetLevel(unsigned level) {
if (level > 19) throw std::invalid_argument("Level out of range, bust be between 0 and 18 inclusive"); // theres a secret level 19 but shhhhhh
two_ls_passes = false;
two_ep_passes = false;
two_cf_passes = false;
exhaustive = false;
_power_iterations = 4;
_error_mode = ErrorMode::Check2;
_endpoint_mode = EndpointMode::PCA;
_search_rounds = 0;
_orderings3 = 0;
_orderings4 = 0;
switch (level) {
case 0:
// Faster/higher quality than stb_dxt default.
_endpoint_mode = EndpointMode::BoundingBoxInt;
break;
case 1:
// Faster/higher quality than stb_dxt default. a bit higher average quality vs. mode 0.
_endpoint_mode = EndpointMode::LeastSquares;
break;
case 2:
// On average mode 2 is a little weaker than modes 0/1, but it's stronger on outliers (very tough textures).
// Slightly stronger than stb_dxt.
// Uses default settings.
break;
case 3:
// Slightly stronger than stb_dxt HIGHQUAL.
two_ls_passes = true;
break;
case 4:
two_ls_passes = true;
_error_mode = ErrorMode::Full;
_power_iterations = 6;
break;
default:
case 5:
// stb_dxt HIGHQUAL + permit 3 color (if it's enabled).
two_ls_passes = true;
_error_mode = ErrorMode::Faster;
break;
case 6:
two_ls_passes = true;
_orderings4 = 1;
_orderings3 = 1;
_error_mode = ErrorMode::Faster;
break;
case 7:
two_ls_passes = true;
_error_mode = ErrorMode::Faster;
_orderings4 = 4;
_orderings3 = 1;
break;
case 8:
two_ls_passes = true;
_error_mode = ErrorMode::Faster;
_orderings4 = 8;
_orderings3 = 1;
break;
case 9:
two_ls_passes = true;
_error_mode = ErrorMode::Check2;
_orderings4 = 11;
_orderings3 = 3;
break;
case 10:
two_ls_passes = true;
_error_mode = ErrorMode::Check2;
_orderings4 = 20;
_orderings3 = 8;
break;
case 11:
two_ls_passes = true;
_error_mode = ErrorMode::Check2;
_orderings4 = 28;
_orderings3 = 16;
break;
case 12:
two_ls_passes = true;
_error_mode = ErrorMode::Check2;
_orderings4 = 32;
_orderings3 = 32;
break;
case 13:
two_ls_passes = true;
two_ep_passes = true;
_error_mode = ErrorMode::Full;
_orderings4 = 32;
_orderings3 = 32;
_search_rounds = 20;
_power_iterations = 6;
break;
case 14:
two_ls_passes = true;
two_ep_passes = true;
_error_mode = ErrorMode::Full;
_orderings4 = 32;
_orderings3 = 32;
_search_rounds = 32;
_power_iterations = 6;
break;
case 15:
two_ls_passes = true;
two_ep_passes = true;
_error_mode = ErrorMode::Full;
_orderings4 = 56;
_orderings3 = 32;
_search_rounds = 32;
_power_iterations = 6;
break;
case 16:
two_ls_passes = true;
two_ep_passes = true;
_error_mode = ErrorMode::Full;
_orderings4 = 80;
_orderings3 = 32;
_search_rounds = 256;
_power_iterations = 6;
break;
case 17:
two_ls_passes = true;
two_ep_passes = true;
_error_mode = ErrorMode::Full;
_orderings4 = 128;
_orderings3 = 32;
_search_rounds = 256;
break;
case 18:
two_ls_passes = true;
two_ep_passes = true;
two_cf_passes = true;
_error_mode = ErrorMode::Full;
_orderings4 = 128;
_orderings3 = 32;
_search_rounds = 256;
_power_iterations = 6;
break;
case 19:
// This hidden mode is *extremely* slow and abuses the encoder. It's just for testing/training.
two_ls_passes = true;
two_ep_passes = true;
two_cf_passes = true;
exhaustive = true;
_error_mode = ErrorMode::Full;
_orderings4 = 128;
_orderings3 = 32;
_search_rounds = 256;
_power_iterations = 6;
break;
}
_orderings4 = clamp(_orderings4, 1U, OrderTable<4>::BestOrderCount);
_orderings3 = clamp(_orderings3, 1U, OrderTable<3>::BestOrderCount);
}
void BC1Encoder::SetOrderings4(unsigned orderings4) { _orderings4 = clamp(orderings4, 1U, OrderTable<4>::BestOrderCount); }
void BC1Encoder::SetOrderings3(unsigned orderings3) { _orderings3 = clamp(orderings3, 1U, OrderTable<3>::BestOrderCount); }
void BC1Encoder::SetOrderings(OrderingPair orderings) {
SetOrderings4(std::get<0>(orderings));
SetOrderings3(std::get<1>(orderings));
}
void BC1Encoder::SetPowerIterations(unsigned int power_iters) { _power_iterations = clamp(power_iters, min_power_iterations, max_power_iterations); }
// Public methods
BC1Block BC1Encoder::EncodeBlock(const ColorBlock<4, 4> &pixels) const {
if (pixels.IsSingleColor()) {
// single-color pixel block, do it the fast way
return WriteBlockSolid(pixels.Get(0, 0));
}
auto metrics = pixels.GetMetrics();
const bool use_likely_orderings = (exhaustive || _orderings3 > 0 || _orderings4 > 0);
bool needs_block_error = use_likely_orderings;
needs_block_error |= (_color_mode == ColorMode::ThreeColor);
needs_block_error |= (_color_mode == ColorMode::ThreeColorBlack) && metrics.has_black;
needs_block_error |= (_error_mode != ErrorMode::None);
needs_block_error |= (_search_rounds > 0);
ErrorMode error_mode = needs_block_error ? _error_mode : ErrorMode::None;
assert(!((_error_mode == ErrorMode::None) && needs_block_error));
const unsigned total_ls_passes = two_ls_passes ? 2 : 1;
const unsigned total_cf_passes = two_cf_passes ? 2 : 1;
const unsigned total_ep_passes = (needs_block_error && two_ep_passes) ? 2 : 1;
// Initial block generation
EncodeResults orig;
EncodeResults result;
for (unsigned round = 0; round < total_ep_passes; round++) {
EndpointMode endpoint_mode = (round == 1) ? EndpointMode::BoundingBox : _endpoint_mode;
EncodeResults trial_orig;
FindEndpoints(trial_orig, pixels, metrics, endpoint_mode);
EncodeResults trial_result = trial_orig;
FindSelectors<ColorMode::FourColor>(trial_result, pixels, error_mode);
RefineBlockLS<ColorMode::FourColor>(trial_result, pixels, metrics, error_mode, total_ls_passes);
if (!needs_block_error || trial_result.error < result.error) {
result = trial_result;
orig = trial_orig;
}
}
// First refinement pass using ordered cluster fit
if (result.error > 0 && use_likely_orderings) {
for (unsigned iter = 0; iter < total_cf_passes; iter++) { RefineBlockCF<ColorMode::FourColor>(result, pixels, metrics, _error_mode, _orderings4); }
}
// try for 3-color block
if (result.error > 0 && (bool)(_color_mode & ColorMode::ThreeColor)) {
EncodeResults trial_result = orig;
FindSelectors<ColorMode::ThreeColor>(trial_result, pixels, ErrorMode::Full);
RefineBlockLS<ColorMode::ThreeColor>(trial_result, pixels, metrics, ErrorMode::Full, total_ls_passes);
// First refinement pass using ordered cluster fit
if (trial_result.error > 0 && use_likely_orderings) {
for (unsigned iter = 0; iter < total_cf_passes; iter++) {
RefineBlockCF<ColorMode::ThreeColor>(trial_result, pixels, metrics, ErrorMode::Full, _orderings3);
}
}
if (trial_result.error < result.error) { result = trial_result; }
}
// try for 3-color block with black
if (result.error > 0 && (_color_mode == ColorMode::ThreeColorBlack) && metrics.has_black && !metrics.max.IsBlack()) {
EncodeResults trial_result;
BlockMetrics metrics_no_black = pixels.GetMetrics(true);
FindEndpoints(trial_result, pixels, metrics_no_black, EndpointMode::PCA, true);
FindSelectors<ColorMode::ThreeColorBlack>(trial_result, pixels, ErrorMode::Full);
RefineBlockLS<ColorMode::ThreeColorBlack>(trial_result, pixels, metrics_no_black, ErrorMode::Full, total_ls_passes);
if (trial_result.error < result.error) { result = trial_result; }
}
// refine endpoints by searching for nearby colors
if (result.error > 0 && _search_rounds > 0) { EndpointSearch(result, pixels); }
return WriteBlock(result);
}
// Private methods
BC1Block BC1Encoder::WriteBlockSolid(Color color) const {
BC1Block block;
uint8_t mask = 0xAA; // 2222
uint16_t min16, max16;
if ((color.r | color.g | color.b) == 0) {
// quick shortcut for all-black blocks
min16 = 0;
max16 = 1;
mask = 0x55; // 1111 (Min value only, max is ignored)
} else {
// why is there no subscript operator for shared_ptr<array>
EncodeResults result;
FindEndpointsSingleColor(result, color, false);
if ((bool)(_color_mode & ColorMode::ThreeColor)) {
EncodeResults result_3color;
FindEndpointsSingleColor(result_3color, color, true);
if (result_3color.error < result.error) { result = result_3color; }
}
min16 = result.low.Pack565Unscaled();
max16 = result.high.Pack565Unscaled();
if (result.solid) {
if (min16 == max16) {
// make sure this isnt accidentally a 3-color block
// so make max16 > min16 (l > h)
if (min16 > 0) {
min16--;
mask = 0; // endpoints are equal so mask doesnt matter
} else {
assert(min16 == 0 && max16 == 0);
max16 = 1;
min16 = 0;
mask = 0x55; // 1111 (Min value only, max is ignored)
}
} else if (max16 < min16) {
std::swap(min16, max16);
mask = 0xFF; // invert mask to 3333
}
assert(max16 > min16);
} else if (max16 > min16) {
std::swap(min16, max16); // assure 3-color blocks
}
}
block.SetLowColor(max16);
block.SetHighColor(min16);
block.selectors[0] = mask;
block.selectors[1] = mask;
block.selectors[2] = mask;
block.selectors[3] = mask;
return block;
}
BC1Block BC1Encoder::WriteBlock(EncodeResults &result) const {
BC1Block block;
BC1Block::UnpackedSelectors selectors;
uint16_t color1 = result.low.Pack565Unscaled();
uint16_t color0 = result.high.Pack565Unscaled();
std::array<uint8_t, 4> lut;
assert(result.color_mode != ColorMode::Incomplete);
if ((bool)(result.color_mode & ColorMode::FourColor)) {
lut = {1, 3, 2, 0};
if (color1 > color0) {
std::swap(color1, color0);
lut = {0, 2, 3, 1};
} else if (color1 == color0) {
if (color1 > 0) {
color1--;
lut = {0, 0, 0, 0};
} else {
assert(color1 == 0 && color0 == 0);
color0 = 1;
color1 = 0;
lut = {1, 1, 1, 1};
}
}
assert(color0 > color1);
} else {
lut = {1, 2, 0, 3};
if (color1 < color0) {
std::swap(color1, color0);
lut = {0, 2, 1, 3};
}
assert(color0 <= color1);
}
for (unsigned i = 0; i < 16; i++) {
unsigned x = i % 4;
unsigned y = i / 4;
selectors[y][x] = lut[result.selectors[i]];
if (result.color_mode == ColorMode::ThreeColor) { assert(selectors[y][x] != 3); }
}
block.SetLowColor(color0);
block.SetHighColor(color1);
block.PackSelectors(selectors);
return block;
}
void BC1Encoder::FindEndpointsSingleColor(EncodeResults &result, Color color, bool is_3color) const {
auto &match5 = is_3color ? _single_match5_half : _single_match5;
auto &match6 = is_3color ? _single_match6_half : _single_match6;
BC1MatchEntry match_r = match5->at(color.r);
BC1MatchEntry match_g = match6->at(color.g);
BC1MatchEntry match_b = match5->at(color.b);
result.color_mode = is_3color ? ColorMode::ThreeColor : ColorMode::FourColor;
result.error = match_r.error + match_g.error + match_b.error;
result.low = Color(match_r.low, match_g.low, match_b.low);
result.high = Color(match_r.high, match_g.high, match_b.high);
// selectors decided when writing, no point deciding them now
}
void BC1Encoder::FindEndpointsSingleColor(EncodeResults &result, const CBlock &pixels, Color color, bool is_3color) const {
std::array<Color, 4> colors = _interpolator->InterpolateBC1(result.low, result.high, is_3color);
Vector4Int result_vector = (Vector4Int)colors[2];
FindEndpointsSingleColor(result, color, is_3color);
result.error = 0;
for (unsigned i = 0; i < 16; i++) {
Vector4Int pixel_vector = (Vector4Int)pixels.Get(i);
auto diff = pixel_vector - result_vector;
result.error += diff.SqrMag();
result.selectors[i] = 1;
}
}
void BC1Encoder::FindEndpoints(EncodeResults &result, const CBlock &pixels, const BlockMetrics &metrics, EndpointMode endpoint_mode, bool ignore_black) const {
if (metrics.is_greyscale) {
// specialized greyscale case
const unsigned fr = pixels.Get(0, 0).r;
if (metrics.max.r - metrics.min.r < 2) {
// single color block
uint8_t fr5 = (uint8_t)scale8To5(fr);
uint8_t fr6 = (uint8_t)scale8To6(fr);
result.low = Color(fr5, fr6, fr5);
result.high = result.low;
} else {
uint8_t lr5 = scale8To5(metrics.min.r);
uint8_t lr6 = scale8To6(metrics.min.r);
uint8_t hr5 = scale8To5(metrics.max.r);
uint8_t hr6 = scale8To6(metrics.max.r);
result.low = Color(lr5, lr6, lr5);
result.high = Color(hr5, hr6, hr5);
}
} else if (endpoint_mode == EndpointMode::LeastSquares) {
// 2D Least Squares approach from Humus's example, with added inset and optimal rounding.
Color diff = Color(metrics.max.r - metrics.min.r, metrics.max.g - metrics.min.g, metrics.max.b - metrics.min.b);
Vector4 l = {0, 0, 0};
Vector4 h = {0, 0, 0};
auto &sums = metrics.sums;
auto &min = metrics.min;
unsigned chan0 = (unsigned)diff.MaxChannelRGB(); // primary axis of the bounding box
l[chan0] = (float)min[chan0];
h[chan0] = (float)min[chan0];
assert((diff[chan0] >= diff[(chan0 + 1) % 3]) && (diff[chan0] >= diff[(chan0 + 2) % 3]));
std::array<unsigned, 3> sums_xy;
for (unsigned i = 0; i < 16; i++) {
auto val = pixels.Get(i);
for (unsigned c = 0; c < 3; c++) { sums_xy[c] += val[chan0] * val[c]; }
}
const unsigned sum_x = (unsigned)sums[chan0];
const unsigned sum_xx = sums_xy[chan0];
float denominator = (float)(16 * sum_xx) - (float)(sum_x * sum_x);
// once per secondary axis, calculate high and low using least squares
if (fabs(denominator) > 1e-8f) {
for (unsigned i = 1; i < 3; i++) {
/* each secondary axis is fitted with a linear formula of the form
* y = ax + b
* where y is the secondary axis and x is the primary axis
* a = (m∑xy - ∑x∑y) / m∑x² - (∑x)²
* b = (∑x²∑y - ∑xy∑x) / m∑x² - (∑x)²
* see Giordano/Weir pg.103 */
const unsigned chan = (chan0 + i) % 3;
const unsigned sum_y = (unsigned)sums[chan];
const unsigned sum_xy = sums_xy[chan];
float a = (float)((16 * sum_xy) - (sum_x * sum_y)) / denominator;
float b = (float)((sum_xx * sum_y) - (sum_xy * sum_x)) / denominator;
l[chan] = b + (a * l[chan0]);
h[chan] = b + (a * h[chan0]);
}
}
// once per axis, inset towards the center by 1/16 of the delta and scale
for (unsigned c = 0; c < 3; c++) {
float inset = (h[c] - l[c]) / 16.0f;
l[c] = ((l[c] + inset) / 255.0f);
h[c] = ((h[c] - inset) / 255.0f);
}
result.low = Color::PreciseRound565(l);
result.high = Color::PreciseRound565(h);
} else if (endpoint_mode == EndpointMode::BoundingBox) {
// Algorithm from icbc.h compress_dxt1_fast()
Vector4 l, h;
const float bias = 8.0f / 255.0f;
// rescale and inset values
for (unsigned c = 0; c < 3; c++) { // heh, c++
l[c] = (float)metrics.min[c] / 255.0f;
h[c] = (float)metrics.max[c] / 255.0f;
float inset = (h[c] - l[c] - bias) / 16.0f;
l[c] += inset;
h[c] -= inset;
}
// Select the correct diagonal across the bounding box
int icov_xz = 0, icov_yz = 0;
for (unsigned i = 0; i < 16; i++) {
int b = (int)pixels.Get(i).b - metrics.avg.b;
icov_xz += b * (int)pixels.Get(i).r - metrics.avg.r;
icov_yz += b * (int)pixels.Get(i).g - metrics.avg.g;
}
if (icov_xz < 0) std::swap(l[0], h[0]);
if (icov_yz < 0) std::swap(l[1], h[1]);
result.low = Color::PreciseRound565(l);
result.high = Color::PreciseRound565(h);
} else if (endpoint_mode == EndpointMode::BoundingBoxInt) {
// Algorithm from icbc.h compress_dxt1_fast(), but converted to integer.
Color min, max;
// rescale and inset values
for (unsigned c = 0; c < 3; c++) {
int inset = ((int)(metrics.max[c] - metrics.min[c]) - 8) >> 4; // 1/16 of delta, with bias
min[c] = clamp255(metrics.min[c] + inset);
max[c] = clamp255(metrics.max[c] - inset);
}
int icov_xz = 0, icov_yz = 0;
for (unsigned i = 0; i < 16; i++) {
int b = (int)pixels.Get(i).b - metrics.avg.b;
icov_xz += b * (int)pixels.Get(i).r - metrics.avg.r;
icov_yz += b * (int)pixels.Get(i).g - metrics.avg.g;
}
if (icov_xz < 0) std::swap(min.r, max.r);
if (icov_yz < 0) std::swap(min.g, max.g);
result.low = min.ScaleTo565();
result.high = max.ScaleTo565();
} else if (endpoint_mode == EndpointMode::PCA) {
// the slow way
// Select 2 colors along the principle axis. (There must be a faster/simpler way.)
auto min = Vector4::FromColorRGB(metrics.min);
auto max = Vector4::FromColorRGB(metrics.max);
auto avg = Vector4::FromColorRGB(metrics.avg);
Vector4 axis = {306, 601, 117}; // Luma vector
Matrix4x4 covariance = Matrix4x4::Identity();
for (unsigned i = 0; i < 16; i++) {
auto val = pixels.Get(i);
if (ignore_black && val.IsBlack()) continue;
auto color_vec = Vector4::FromColorRGB(val);
Vector4 diff = color_vec - avg;
for (unsigned c1 = 0; c1 < 3; c1++) {
for (unsigned c2 = c1; c2 < 3; c2++) {
covariance[c1][c2] += (diff[c1] * diff[c2]);
assert(c1 <= c2);
}
}
}
covariance /= 255.0f;
covariance.Mirror();
Vector4 delta = max - min;
// realign r and g axes to match
if (covariance[0][2] < 0) delta[0] = -delta[0]; // r vs b
if (covariance[1][2] < 0) delta[1] = -delta[1]; // g vs b
// using the covariance matrix, stretch the delta vector towards the primary axis of the data using power iteration
// the end result of this may actually be the same as the least squares approach, will have to do more research
for (unsigned power_iter = 0; power_iter < _power_iterations; power_iter++) { delta = covariance * delta; }
// if we found any correlation, then this is our new axis. otherwise we fallback to the luma vector
float k = delta.MaxAbs(3);
if (k >= 2) { axis = delta * (2048.0f / k); }
axis *= 16;
float min_dot = INFINITY;
float max_dot = -INFINITY;
unsigned min_index = 0, max_index = 0;
for (unsigned i = 0; i < 16; i++) {
auto val = pixels.Get(i);
if (ignore_black && val.IsBlack()) continue;
auto color_vec = Vector4::FromColorRGB(val);
// since axis is constant here, I dont think its magnitude actually matters,
// since we only care about the min or max dot product
float dot = color_vec.Dot(axis);
if (dot > max_dot) {
max_dot = dot;
max_index = i;
}
if (dot < min_dot) {
min_dot = dot;
min_index = i;
}
}
result.low = pixels.Get(min_index).ScaleTo565();
result.high = pixels.Get(max_index).ScaleTo565();
}
result.color_mode = ColorMode::Incomplete;
}
template <BC1Encoder::ColorMode M> void BC1Encoder::FindSelectors(EncodeResults &result, const CBlock &pixels, ErrorMode error_mode) const {
assert(!((error_mode != ErrorMode::Full) && (bool)(M & ColorMode::ThreeColor)));
const int color_count = (unsigned)M & 0x0F;
std::array<Color, 4> colors = _interpolator->InterpolateBC1(result.low, result.high, color_count == 3);
std::array<Vector4Int, 4> color_vectors;
if (color_count == 4) {
color_vectors = {Vector4Int::FromColorRGB(colors[0]), Vector4Int::FromColorRGB(colors[2]), Vector4Int::FromColorRGB(colors[3]),
Vector4Int::FromColorRGB(colors[1])};
} else {
color_vectors = {Vector4Int::FromColorRGB(colors[0]), Vector4Int::FromColorRGB(colors[2]), Vector4Int::FromColorRGB(colors[1]),
Vector4Int::FromColorRGB(colors[3])};
}
unsigned total_error = 0;
if (error_mode == ErrorMode::None || error_mode == ErrorMode::Faster) {
Vector4Int axis = color_vectors[3] - color_vectors[0];
std::array<int, 4> dots;
for (unsigned i = 0; i < 4; i++) { dots[i] = axis.Dot(color_vectors[i]); }
int t0 = dots[0] + dots[1], t1 = dots[1] + dots[2], t2 = dots[2] + dots[3];
axis *= 2;
for (unsigned i = 0; i < 16; i++) {
Vector4Int pixel_vector = Vector4Int::FromColorRGB(pixels.Get(i));
int dot = axis.Dot(pixel_vector);
uint8_t level = (dot <= t0) + (dot < t1) + (dot < t2);
uint8_t selector = 3 - level;
assert(level < 4);
assert(selector < 4);
if (error_mode == ErrorMode::Faster) {
// llvm is just going to unswitch this anyways so its not an issue
auto diff = pixel_vector - color_vectors[selector];
total_error += diff.SqrMag();
if (i % 4 != 0 && total_error >= result.error) break; // check only once per row if we're generating too much error
}
result.selectors[i] = selector;
}
} else if (error_mode == ErrorMode::Check2) {
Vector4Int axis = color_vectors[3] - color_vectors[0];
const float f = 4.0f / ((float)axis.SqrMag() + .00000125f);
for (unsigned i = 0; i < 16; i++) {
Vector4Int pixel_vector = Vector4Int::FromColorRGB(pixels.Get(i));
auto diff = pixel_vector - color_vectors[0];
float sel_f = (float)diff.Dot(axis) * f + 0.5f;
uint8_t sel = (uint8_t)clampi((int)sel_f, 1, 3);
unsigned err0 = (color_vectors[sel - 1] - pixel_vector).SqrMag();
unsigned err1 = (color_vectors[sel] - pixel_vector).SqrMag();
uint8_t best_sel = sel;
unsigned best_err = err1;
if (err0 == err1) {
// prefer non-interpolation
if ((best_sel) == 1) best_sel = 0;
} else if (err0 < best_err) {
best_sel = sel - 1;
best_err = err0;
}
total_error += best_err;
if (total_error >= result.error) break;
result.selectors[i] = best_sel;
}
} else if (error_mode == ErrorMode::Full) {
unsigned max_sel = (bool)(M == ColorMode::ThreeColor) ? 3 : 4;
for (unsigned i = 0; i < 16; i++) {
unsigned best_error = UINT_MAX;
uint8_t best_sel = 0;
Vector4Int pixel_vector = Vector4Int::FromColorRGB(pixels.Get(i));
// exhasustively check every pixel's distance from each color, and calculate the error
for (uint8_t j = 0; j < max_sel; j++) {
auto diff = color_vectors[j] - pixel_vector;
unsigned err = diff.SqrMag();
if (err < best_error || ((err == best_error) && (j == 3))) {
best_error = err;
best_sel = j;
}
}
total_error += best_error;
if (total_error >= result.error) { break; }
assert(best_sel < max_sel);
result.selectors[i] = best_sel;
}
} else {
assert(false);
}
result.error = total_error;
result.color_mode = M;
}
template <BC1Encoder::ColorMode M> bool BC1Encoder::RefineEndpointsLS(EncodeResults &result, const CBlock &pixels, BlockMetrics metrics) const {
const int color_count = (unsigned)M & 0x0F;
static_assert(color_count == 3 || color_count == 4);
assert(result.color_mode != ColorMode::Incomplete);
int denominator = color_count - 1;
Vector4 q00 = {0, 0, 0};
Vector4 matrix = Vector4(0);
for (unsigned i = 0; i < 16; i++) {
const Color color = pixels.Get(i);
const uint8_t sel = result.selectors[i];
if ((bool)(M & ColorMode::ThreeColorBlack) && color.IsBlack()) continue;
if ((bool)(M & ColorMode::ThreeColor) && sel == 3U) continue; // NOTE: selectors for 3-color are in linear order here, but not in original
assert(sel < color_count);
const Vector4Int color_vector = Vector4Int::FromColorRGB(color);
q00 += color_vector * sel;
matrix += OrderTable<color_count>::Weights[sel];
}
// invert matrix
float det = matrix.Determinant2x2(); // z00 * z11 - z01 * z10;
if (fabs(det) < 1e-8f) {
result.color_mode = ColorMode::Incomplete;
return false;
}
std::swap(matrix[0], matrix[3]);
matrix *= Vector4(1, -1, -1, 1);
matrix *= ((float)denominator / 255.0f) / det;
Vector4 q10 = (metrics.sums * denominator) - q00;
Vector4 low = (matrix[0] * q00) + (matrix[1] * q10);
Vector4 high = (matrix[2] * q00) + (matrix[3] * q10);
result.color_mode = M;
result.low = Color::PreciseRound565(low);
result.high = Color::PreciseRound565(high);
return true;
}
template <BC1Encoder::ColorMode M> void BC1Encoder::RefineEndpointsLS(EncodeResults &result, std::array<Vector4, 17> &sums, Vector4 &matrix, Hash hash) const {
const int color_count = (unsigned)M & 0x0F;
static_assert(color_count == 3 || color_count == 4);
assert(result.color_mode != ColorMode::Incomplete);
int denominator = color_count - 1;
Vector4 q10 = {0, 0, 0};
unsigned level = 0;
Histogram<color_count> h = OrderTable<color_count>::Orders[hash];
for (unsigned i = 0; i < (color_count - 1); i++) {
level += h[i];
q10 += sums[level];
}
Vector4 q00 = (sums[16] * (float)denominator) - q10;
Vector4 low = (matrix[0] * q00) + (matrix[1] * q10);
Vector4 high = (matrix[2] * q00) + (matrix[3] * q10);
result.color_mode = M;
result.low = Color::PreciseRound565(low);
result.high = Color::PreciseRound565(high);
}
template <BC1Encoder::ColorMode M>
void BC1Encoder::RefineBlockLS(EncodeResults &result, const CBlock &pixels, const BlockMetrics &metrics, ErrorMode error_mode, unsigned passes) const {
assert(error_mode != ErrorMode::None || passes == 1);
for (unsigned pass = 0; pass < passes; pass++) {
EncodeResults trial_result = result;
Vector4 low, high;
bool multicolor = RefineEndpointsLS<ColorMode::FourColor>(trial_result, pixels, metrics);
if (!multicolor) {
FindEndpointsSingleColor(trial_result, pixels, metrics.avg, (M != ColorMode::FourColor));
} else {
FindSelectors<M>(trial_result, pixels, error_mode);
}
if (trial_result.low == result.low && trial_result.high == result.high) break;
if (error_mode == ErrorMode::None || trial_result.error < result.error) {
result = trial_result;
} else {
return;
}
}
}
template <BC1Encoder::ColorMode M>
void BC1Encoder::RefineBlockCF(EncodeResults &result, const CBlock &pixels, const BlockMetrics &metrics, ErrorMode error_mode, unsigned orderings) const {
const int color_count = (unsigned)M & 0x0F;
static_assert(color_count == 3 || color_count == 4);
assert(result.color_mode != ColorMode::Incomplete);
using OrderTable = OrderTable<color_count>;
using Hist = Histogram<color_count>;
EncodeResults orig = result;
Hist h = Hist(orig.selectors);
Hash start_hash = OrderTable::GetHash(h);
Vector4 axis = orig.high.ScaleFrom565() - orig.low.ScaleFrom565();
std::array<Vector4, 16> color_vectors;
std::array<uint32_t, 16> dots;
for (int i = 0; i < 16; i++) {
color_vectors[(unsigned)i] = Vector4::FromColorRGB(pixels.Get(i));
int dot = 0x1000000 + (int)color_vectors[(unsigned)i].Dot(axis);
assert(dot >= 0);
dots[(unsigned)i] = (uint32_t)(dot << 4) | i;
}
std::sort(dots.begin(), dots.end());
// we now have a list of indices and their dot products along the primary axis
std::array<Vector4, 17> sums;
for (unsigned i = 0; i < 16; i++) {
const unsigned p = dots[i] & 0xF;
sums[i + 1] = sums[i] + color_vectors[p];
}
const unsigned q_total = exhaustive ? OrderTable::OrderCount : orderings;
for (Hash q = 0; q < q_total; q++) {
Hash trial_hash = exhaustive ? q : OrderTable::BestOrders[start_hash][q];
Vector4 trial_matrix = OrderTable::GetFactors(trial_hash);
EncodeResults trial_result = orig;
Vector4 low, high;
if (OrderTable::IsSingleColor(trial_hash)) {
FindEndpointsSingleColor(trial_result, pixels, metrics.avg, (color_count == 3));
} else {
RefineEndpointsLS<M>(trial_result, sums, trial_matrix, trial_hash);
FindSelectors<M>(trial_result, pixels, error_mode);
}
if (trial_result.error < result.error) { result = trial_result; }
if (trial_result.error == 0) break;
}
}
void BC1Encoder::EndpointSearch(EncodeResults &result, const CBlock &pixels) const {
if (result.solid) return;
static const std::array<Vector4Int, 16> Voxels = {{
{1, 0, 0, 3}, // 0
{0, 1, 0, 4}, // 1
{0, 0, 1, 5}, // 2
{-1, 0, 0, 0}, // 3
{0, -1, 0, 1}, // 4
{0, 0, -1, 2}, // 5
{1, 1, 0, 9}, // 6
{1, 0, 1, 10}, // 7
{0, 1, 1, 11}, // 8
{-1, -1, 0, 6}, // 9
{-1, 0, -1, 7}, // 10
{0, -1, -1, 8}, // 11
{-1, 1, 0, 13}, // 12
{1, -1, 0, 12}, // 13
{0, -1, 1, 15}, // 14
{0, 1, -1, 14}, // 15
}};
unsigned prev_improvement_index = 0;
int forbidden_direction = -1;
for (unsigned i = 0; i < _search_rounds; i++) {
const unsigned voxel_index = (unsigned)(i & 15);
assert((unsigned)Voxels[(unsigned)Voxels[voxel_index][3]][3] == voxel_index); // make sure voxels are symmetrical
if ((int)(i & 31) == forbidden_direction) continue;
Vector4Int delta = Voxels[voxel_index];
EncodeResults trial_result = result;
if (i & 16) {
trial_result.low.r = (uint8_t)clamp(trial_result.low.r + delta[0], 0, 31);
trial_result.low.g = (uint8_t)clamp(trial_result.low.g + delta[1], 0, 63);
trial_result.low.b = (uint8_t)clamp(trial_result.low.b + delta[2], 0, 31);
} else {
trial_result.high.r = (uint8_t)clamp(trial_result.high.r + delta[0], 0, 31);
trial_result.high.g = (uint8_t)clamp(trial_result.high.g + delta[1], 0, 63);
trial_result.high.b = (uint8_t)clamp(trial_result.high.b + delta[2], 0, 31);
}
switch (result.color_mode) {
default:
case ColorMode::FourColor:
FindSelectors<ColorMode::FourColor>(trial_result, pixels, _error_mode);
break;
case ColorMode::ThreeColor:
FindSelectors<ColorMode::ThreeColor>(trial_result, pixels, ErrorMode::Full);
break;
case ColorMode::ThreeColorBlack:
FindSelectors<ColorMode::ThreeColorBlack>(trial_result, pixels, ErrorMode::Full);
break;
}
if (trial_result.error < result.error) {
result = trial_result;
forbidden_direction = delta[3] | (int)(i & 16);
prev_improvement_index = i;
}
if (i - prev_improvement_index > 32) break;
}
}
} // namespace quicktex::s3tc
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