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93 lines
3.2 KiB
C++
93 lines
3.2 KiB
C++
/* Quicktex Texture Compression Library
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Copyright (C) 2021-2022 Andrew Cassidy <drewcassidy@me.com>
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Partially derived from rgbcx.h written by Richard Geldreich <richgel99@gmail.com>
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and licenced under the public domain
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <array>
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#include <cstdint>
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#include <memory>
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#include "../../util.h"
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#include "../interpolator/Interpolator.h"
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namespace quicktex::s3tc {
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struct BC1MatchEntry {
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uint8_t high;
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uint8_t low;
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uint8_t error;
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};
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using MatchList = std::array<BC1MatchEntry, 256>;
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using MatchListPtr = std::shared_ptr<MatchList>;
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using InterpolatorPtr = std::shared_ptr<Interpolator>;
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/**
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* Lookup table for single-color blocks
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* @tparam B Number of bits (5 or 6)
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* @tparam N Number of colors (3 or 4)
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*/
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template <size_t B, size_t N> MatchListPtr SingleColorTable(InterpolatorPtr interpolator) {
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constexpr size_t Size = 1 << B;
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MatchListPtr matches = std::make_shared<MatchList>();
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static_assert((B == 5 && Size == 32) || (B == 6 && Size == 64));
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static_assert(N == 4 || N == 3);
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bool ideal = interpolator->IsIdeal();
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bool use_8bit = interpolator->CanInterpolate8Bit();
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for (unsigned i = 0; i < 256; i++) {
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unsigned error = 256;
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// TODO: Can probably avoid testing for values that definitely wont yield good results,
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// e.g. low8 and high8 both much smaller or larger than index
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for (uint8_t low = 0; low < Size; low++) {
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uint8_t low8 = (B == 5) ? scale5To8(low) : scale6To8(low);
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for (uint8_t high = 0; high < Size; high++) {
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uint8_t high8 = (B == 5) ? scale5To8(high) : scale6To8(high);
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uint8_t value;
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if (use_8bit) {
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value = interpolator->Interpolate8(high8, low8);
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} else {
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value = (B == 5) ? interpolator->Interpolate5(high, low) : interpolator->Interpolate6(high, low);
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}
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unsigned new_error = iabs(value - (int)i);
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// We only need to factor in 3% error in BC1 ideal mode.
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if (ideal) new_error += (iabs(high8 - (int)low8) * 3) / 100;
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if ((new_error < error) || (new_error == error && low == high)) {
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assert(new_error <= UINT8_MAX);
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(*matches)[i].low = (uint8_t)low;
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(*matches)[i].high = (uint8_t)high;
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(*matches)[i].error = (uint8_t)new_error;
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error = new_error;
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}
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}
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}
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}
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return matches;
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}
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} // namespace quicktex::s3tc
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