495 lines
15 KiB
C++
495 lines
15 KiB
C++
#include "blurhash.hpp"
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#include <algorithm>
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#include <array>
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#include <cassert>
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#include <cmath>
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#include <numbers>
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#include <stdexcept>
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#ifdef DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
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#if __has_include(<doctest.h>)
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#include <doctest.h>
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#else
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#include <doctest/doctest.h>
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#endif
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#endif
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using namespace std::literals;
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namespace {
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constexpr std::array<char, 84> int_to_b83{
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"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~"};
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std::string
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leftPad(std::string str, size_t len)
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{
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if (str.size() >= len)
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return str;
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return str.insert(0, len - str.size(), '0');
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}
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constexpr std::array<int, 255> b83_to_int = []() constexpr
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{
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std::array<int, 255> a{};
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for (auto &e : a)
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e = -1;
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for (int i = 0; i < 83; i++) {
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a[static_cast<unsigned char>(int_to_b83[i])] = i;
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}
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return a;
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}
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();
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std::string
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encode83(int value)
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{
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std::string buffer;
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do {
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buffer += int_to_b83[value % 83];
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} while ((value = value / 83));
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std::reverse(buffer.begin(), buffer.end());
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return buffer;
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}
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struct Components
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{
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int x, y;
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};
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int
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packComponents(const Components &c) noexcept
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{
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return (c.x - 1) + (c.y - 1) * 9;
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}
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Components
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unpackComponents(int c) noexcept
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{
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return {c % 9 + 1, c / 9 + 1};
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}
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int
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decode83(std::string_view value)
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{
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int temp = 0;
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for (char c : value)
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if (b83_to_int[static_cast<unsigned char>(c)] < 0)
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throw std::invalid_argument("invalid character in blurhash");
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for (char c : value)
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temp = temp * 83 + b83_to_int[static_cast<unsigned char>(c)];
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return temp;
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}
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float
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decodeMaxAC(int quantizedMaxAC) noexcept
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{
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return static_cast<float>(quantizedMaxAC + 1) / 166.f;
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}
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float
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decodeMaxAC(std::string_view maxAC)
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{
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assert(maxAC.size() == 1);
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return decodeMaxAC(decode83(maxAC));
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}
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int
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encodeMaxAC(float maxAC) noexcept
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{
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return std::max(0, std::min(82, int(maxAC * 166 - 0.5f)));
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}
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float
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srgbToLinear(int value) noexcept
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{
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auto srgbToLinearF = [](float x) {
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if (x <= 0.0f)
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return 0.0f;
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else if (x >= 1.0f)
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return 1.0f;
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else if (x < 0.04045f)
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return x / 12.92f;
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else
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return std::pow((x + 0.055f) / 1.055f, 2.4f);
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};
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return srgbToLinearF(static_cast<float>(value) / 255.f);
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}
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int
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linearToSrgb(float value) noexcept
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{
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auto linearToSrgbF = [](float x) -> float {
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if (x <= 0.0f)
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return 0.0f;
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else if (x >= 1.0f)
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return 1.0f;
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else if (x < 0.0031308f)
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return x * 12.92f;
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else
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return std::pow(x, 1.0f / 2.4f) * 1.055f - 0.055f;
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};
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return int(linearToSrgbF(value) * 255.f + 0.5f);
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}
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struct Color
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{
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float r, g, b;
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Color &operator*=(float scale)
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{
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r *= scale;
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g *= scale;
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b *= scale;
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return *this;
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}
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friend Color operator*(Color lhs, float rhs) { return (lhs *= rhs); }
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Color &operator/=(float scale)
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{
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r /= scale;
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g /= scale;
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b /= scale;
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return *this;
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}
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Color &operator+=(const Color &rhs)
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{
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r += rhs.r;
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g += rhs.g;
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b += rhs.b;
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return *this;
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}
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};
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Color
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decodeDC(int value)
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{
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const int intR = value >> 16;
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const int intG = (value >> 8) & 255;
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const int intB = value & 255;
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return {srgbToLinear(intR), srgbToLinear(intG), srgbToLinear(intB)};
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}
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Color
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decodeDC(std::string_view value)
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{
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assert(value.size() == 4);
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return decodeDC(decode83(value));
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}
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int
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encodeDC(const Color &c)
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{
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return (linearToSrgb(c.r) << 16) + (linearToSrgb(c.g) << 8) + linearToSrgb(c.b);
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}
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float
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signPow(float value, float exp)
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{
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return std::copysign(std::pow(std::abs(value), exp), value);
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}
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int
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encodeAC(const Color &c, float maximumValue)
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{
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auto quantR =
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int(std::max(0., std::min(18., std::floor(signPow(c.r / maximumValue, 0.5) * 9 + 9.5))));
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auto quantG =
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int(std::max(0., std::min(18., std::floor(signPow(c.g / maximumValue, 0.5) * 9 + 9.5))));
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auto quantB =
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int(std::max(0., std::min(18., std::floor(signPow(c.b / maximumValue, 0.5) * 9 + 9.5))));
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return quantR * 19 * 19 + quantG * 19 + quantB;
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}
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Color
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decodeAC(int value, float maximumValue)
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{
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auto quantR = value / (19 * 19);
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auto quantG = (value / 19) % 19;
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auto quantB = value % 19;
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return {signPow((float(quantR) - 9) / 9, 2) * maximumValue,
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signPow((float(quantG) - 9) / 9, 2) * maximumValue,
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signPow((float(quantB) - 9) / 9, 2) * maximumValue};
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}
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Color
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decodeAC(std::string_view value, float maximumValue)
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{
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return decodeAC(decode83(value), maximumValue);
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}
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std::vector<float>
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bases_for(size_t dimension, size_t components)
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{
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std::vector<float> bases(dimension * components, 0.f);
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auto scale = std::numbers::pi_v<float> / float(dimension);
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for (size_t x = 0; x < dimension; x++) {
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for (size_t nx = 0; nx < size_t(components); nx++) {
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bases[x * components + nx] = std::cos(scale * float(nx * x));
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}
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}
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return bases;
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}
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}
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namespace blurhash {
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Image
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decode(std::string_view blurhash, size_t width, size_t height, size_t bytesPerPixel) noexcept
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{
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Image i{};
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if (blurhash.size() < 10)
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return i;
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Components components{};
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std::vector<Color> values;
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values.reserve(blurhash.size() / 2);
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try {
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components = unpackComponents(decode83(blurhash.substr(0, 1)));
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if (components.x < 1 || components.y < 1 ||
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blurhash.size() != size_t(1 + 1 + 4 + (components.x * components.y - 1) * 2))
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return {};
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auto maxAC = decodeMaxAC(blurhash.substr(1, 1));
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Color average = decodeDC(blurhash.substr(2, 4));
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values.push_back(average);
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for (size_t c = 6; c < blurhash.size(); c += 2)
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values.push_back(decodeAC(blurhash.substr(c, 2), maxAC));
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} catch (std::invalid_argument &) {
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return {};
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}
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i.image = decltype(i.image)(height * width * bytesPerPixel, 255);
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std::vector<float> basis_x = bases_for(width, components.x);
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std::vector<float> basis_y = bases_for(height, components.y);
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for (size_t y = 0; y < height; y++) {
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for (size_t x = 0; x < width; x++) {
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Color c{};
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for (size_t nx = 0; nx < size_t(components.x); nx++) {
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for (size_t ny = 0; ny < size_t(components.y); ny++) {
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float basis = basis_x[x * components.x + nx] *
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basis_y[y * components.y + ny];
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c += values[nx + ny * components.x] * basis;
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}
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}
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i.image[(y * width + x) * bytesPerPixel + 0] =
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static_cast<unsigned char>(linearToSrgb(c.r));
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i.image[(y * width + x) * bytesPerPixel + 1] =
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static_cast<unsigned char>(linearToSrgb(c.g));
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i.image[(y * width + x) * bytesPerPixel + 2] =
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static_cast<unsigned char>(linearToSrgb(c.b));
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}
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}
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i.height = height;
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i.width = width;
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return i;
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}
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std::string
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encode(unsigned char *image, size_t width, size_t height, int components_x, int components_y)
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{
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if (width < 1 || height < 1 || components_x < 1 || components_x > 9 || components_y < 1 ||
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components_y > 9 || !image)
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return "";
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std::vector<float> basis_x = bases_for(width, components_x);
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std::vector<float> basis_y = bases_for(height, components_y);
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std::vector<Color> factors(components_x * components_y, Color{});
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for (size_t y = 0; y < height; y++) {
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for (size_t x = 0; x < width; x++) {
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Color linear{srgbToLinear(image[3 * x + 0 + y * width * 3]),
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srgbToLinear(image[3 * x + 1 + y * width * 3]),
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srgbToLinear(image[3 * x + 2 + y * width * 3])};
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// other half of normalization.
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linear *= 1.f / static_cast<float>(width);
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for (size_t ny = 0; ny < size_t(components_y); ny++) {
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for (size_t nx = 0; nx < size_t(components_x); nx++) {
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float basis = basis_x[x * size_t(components_x) + nx] *
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basis_y[y * size_t(components_y) + ny];
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factors[ny * components_x + nx] += linear * basis;
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}
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}
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}
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}
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// scale by normalization. Half the scaling is done in the previous loop to prevent going
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// too far outside the float range.
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for (size_t i = 0; i < factors.size(); i++) {
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float normalisation = (i == 0) ? 1 : 2;
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float scale = normalisation / static_cast<float>(height);
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factors[i] *= scale;
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}
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assert(factors.size() > 0);
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auto dc = factors.front();
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factors.erase(factors.begin());
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std::string h;
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h += leftPad(encode83(packComponents({components_x, components_y})), 1);
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float maximumValue;
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if (!factors.empty()) {
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float actualMaximumValue = 0;
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for (auto ac : factors) {
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actualMaximumValue = std::max({
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std::abs(ac.r),
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std::abs(ac.g),
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std::abs(ac.b),
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actualMaximumValue,
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});
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}
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int quantisedMaximumValue = encodeMaxAC(actualMaximumValue);
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maximumValue = ((float)quantisedMaximumValue + 1) / 166;
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h += leftPad(encode83(quantisedMaximumValue), 1);
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} else {
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maximumValue = 1;
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h += leftPad(encode83(0), 1);
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}
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h += leftPad(encode83(encodeDC(dc)), 4);
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for (auto ac : factors)
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h += leftPad(encode83(encodeAC(ac, maximumValue)), 2);
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return h;
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}
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}
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#ifdef DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
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TEST_CASE("component packing")
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{
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for (int i = 0; i < 9 * 9; i++)
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CHECK(packComponents(unpackComponents(i)) == i);
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}
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TEST_CASE("encode83")
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{
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CHECK(encode83(0) == "0");
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CHECK(encode83(packComponents({4, 3})) == "L");
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CHECK(encode83(packComponents({4, 4})) == "U");
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CHECK(encode83(packComponents({8, 4})) == "Y");
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CHECK(encode83(packComponents({2, 1})) == "1");
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}
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TEST_CASE("decode83")
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{
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CHECK(packComponents({4, 3}) == decode83("L"));
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CHECK(packComponents({4, 4}) == decode83("U"));
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CHECK(packComponents({8, 4}) == decode83("Y"));
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CHECK(packComponents({2, 1}) == decode83("1"));
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}
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TEST_CASE("maxAC")
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{
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for (int i = 0; i < 83; i++)
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CHECK(encodeMaxAC(decodeMaxAC(i)) == i);
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CHECK(std::abs(decodeMaxAC("l"sv) - 0.289157f) < 0.00001f);
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}
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TEST_CASE("DC")
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{
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CHECK(encode83(encodeDC(decodeDC("MF%n"))) == "MF%n"sv);
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CHECK(encode83(encodeDC(decodeDC("HV6n"))) == "HV6n"sv);
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CHECK(encode83(encodeDC(decodeDC("F5]+"))) == "F5]+"sv);
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CHECK(encode83(encodeDC(decodeDC("Pj0^"))) == "Pj0^"sv);
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CHECK(encode83(encodeDC(decodeDC("O2?U"))) == "O2?U"sv);
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}
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TEST_CASE("AC")
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{
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auto h = "00%#MwS|WCWEM{R*bbWBbH"sv;
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for (size_t i = 0; i < h.size(); i += 2) {
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auto s = h.substr(i, 2);
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const auto maxAC = 0.289157f;
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CHECK(leftPad(encode83(encodeAC(decodeAC(decode83(s), maxAC), maxAC)), 2) == s);
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}
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}
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TEST_CASE("decode")
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{
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blurhash::Image i1 = blurhash::decode("LEHV6nWB2yk8pyoJadR*.7kCMdnj", 360, 200);
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CHECK(i1.width == 360);
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CHECK(i1.height == 200);
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CHECK(i1.image.size() == i1.height * i1.width * 3);
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CHECK(i1.image[0] == 135);
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CHECK(i1.image[1] == 164);
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CHECK(i1.image[2] == 177);
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CHECK(i1.image[10000] == 173);
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CHECK(i1.image[10001] == 176);
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CHECK(i1.image[10002] == 163);
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// stbi_write_bmp("test.bmp", i1.width, i1.height, 3, (void *)i1.image.data());
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i1 = blurhash::decode("LGF5]+Yk^6#M@-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 360);
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CHECK(i1.height == 200);
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CHECK(i1.image.size() == i1.height * i1.width * 3);
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// stbi_write_bmp("test2.bmp", i1.width, i1.height, 3, (void *)i1.image.data());
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// invalid inputs
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i1 = blurhash::decode(" LGF5]+Yk^6#M@-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 0);
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CHECK(i1.height == 0);
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CHECK(i1.image.size() == 0);
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i1 = blurhash::decode(" LGF5]+Yk^6#M@-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 0);
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CHECK(i1.height == 0);
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CHECK(i1.image.size() == 0);
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i1 = blurhash::decode("LGF5]+Yk^6# M@-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 0);
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CHECK(i1.height == 0);
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CHECK(i1.image.size() == 0);
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i1 = blurhash::decode("LGF5]+Yk^6# M@-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 0);
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CHECK(i1.height == 0);
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CHECK(i1.image.size() == 0);
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i1 = blurhash::decode("LGF5]+Yk^6# @-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 0);
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CHECK(i1.height == 0);
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CHECK(i1.image.size() == 0);
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i1 = blurhash::decode(" GF5]+Yk^6#M@-5c,1J5@[or[Q6.", 360, 200);
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CHECK(i1.width == 0);
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CHECK(i1.height == 0);
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CHECK(i1.image.size() == 0);
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}
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TEST_CASE("encode")
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{
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CHECK(blurhash::encode(nullptr, 360, 200, 4, 3) == "");
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std::vector<unsigned char> black(360 * 200 * 3, 0);
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CHECK(blurhash::encode(black.data(), 0, 200, 4, 3) == "");
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CHECK(blurhash::encode(black.data(), 360, 0, 4, 3) == "");
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CHECK(blurhash::encode(black.data(), 360, 200, 0, 3) == "");
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CHECK(blurhash::encode(black.data(), 360, 200, 4, 0) == "");
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CHECK(blurhash::encode(black.data(), 360, 200, 4, 3) == "L00000fQfQfQfQfQfQfQfQfQfQfQ");
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}
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#endif
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