quicktex/quicktex/s3tc/bc4/BC4Block.h

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/* Python-rgbcx Texture Compression Library
Copyright (C) 2021 Andrew Cassidy <drewcassidy@me.com>
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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
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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
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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
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#pragma once
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#include <array>
#include <cassert>
#include <cstdint>
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#include <cstdlib>
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#include "../../Color.h"
#include "../../util.h"
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#include "../bc1/BC1Block.h"
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namespace quicktex::s3tc {
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class alignas(8) BC4Block {
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public:
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static constexpr int Width = 4;
static constexpr int Height = 4;
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using SelectorArray = std::array<std::array<uint8_t, Width>, Height>;
using AlphaPair = std::pair<uint8_t, uint8_t>;
constexpr BC4Block() {
static_assert(sizeof(BC4Block) == 8);
static_assert(sizeof(std::array<BC4Block, 10>) == 8 * 10);
alpha0 = alpha1 = 0;
SetSelectorBits(0);
}
constexpr BC4Block(uint8_t valpha0, uint8_t valpha1, const SelectorArray& selectors) {
alpha0 = valpha0;
alpha1 = valpha1;
SetSelectors(selectors);
}
inline bool Is6Value() const { return alpha0 <= alpha1; }
AlphaPair GetAlphas() const { return AlphaPair(alpha0, alpha1); }
void SetAlphas(AlphaPair as) {
alpha0 = as.first;
alpha1 = as.second;
}
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inline uint64_t GetSelectorBits() const {
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auto packed = Pack<uint8_t, uint64_t, 8, SelectorSize>(selectors);
assert(packed <= SelectorBitsMax);
return packed;
}
void SetSelectorBits(uint64_t packed) {
assert(packed <= SelectorBitsMax);
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selectors = Unpack<uint64_t, uint8_t, 8, SelectorSize>(packed);
}
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SelectorArray GetSelectors() const {
SelectorArray unpacked;
auto rows = Unpack<uint64_t, uint16_t, 12, Width>(GetSelectorBits());
for (unsigned i = 0; i < Height; i++) {
auto row = Unpack<uint16_t, uint8_t, SelectorBits, Width>(rows[i]);
unpacked[i] = row;
}
return unpacked;
}
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void SetSelectors(const SelectorArray& unpacked) {
std::array<uint16_t, Height> rows;
for (int i = 0; i < Height; i++) { rows[i] = Pack<uint8_t, uint16_t, SelectorBits, Width>(unpacked[i]); }
auto packed = Pack<uint16_t, uint64_t, 12, Height>(rows);
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SetSelectorBits(packed);
}
static inline std::array<uint8_t, 8> GetValues6(uint32_t l, uint32_t h) {
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return {static_cast<uint8_t>(l),
static_cast<uint8_t>(h),
static_cast<uint8_t>((l * 4 + h) / 5),
static_cast<uint8_t>((l * 3 + h * 2) / 5),
static_cast<uint8_t>((l * 2 + h * 3) / 5),
static_cast<uint8_t>((l + h * 4) / 5),
0,
255};
}
static inline std::array<uint8_t, 8> GetValues8(uint32_t l, uint32_t h) {
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return {static_cast<uint8_t>(l),
static_cast<uint8_t>(h),
static_cast<uint8_t>((l * 6 + h) / 7),
static_cast<uint8_t>((l * 5 + h * 2) / 7),
static_cast<uint8_t>((l * 4 + h * 3) / 7),
static_cast<uint8_t>((l * 3 + h * 4) / 7),
static_cast<uint8_t>((l * 2 + h * 5) / 7),
static_cast<uint8_t>((l + h * 6) / 7)};
}
static inline std::array<uint8_t, 8> GetValues(uint32_t l, uint32_t h) {
if (l > h)
return GetValues8(l, h);
else
return GetValues6(l, h);
}
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constexpr static inline size_t EndpointSize = 1;
constexpr static inline size_t SelectorSize = 6;
constexpr static inline uint8_t SelectorBits = 3;
constexpr static inline uint8_t SelectorValues = 1 << SelectorBits;
constexpr static inline uint8_t SelectorMask = SelectorValues - 1;
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constexpr static inline uint64_t SelectorBitsMax = (1ULL << (8U * SelectorSize)) - 1U;
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uint8_t alpha0;
uint8_t alpha1;
private:
std::array<uint8_t, SelectorSize> selectors;
};
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} // namespace quicktex::s3tc