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build*
.clang-format
.DS_Store
.kdev4/
neochat.kdev4
compile_commands.json
.cache/
.vscode/
kate.project.ctags.*
*.user
.flatpak-builder/
.idea/
cmake-build-*
src/res.generated.qrc
.qmlls.ini

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Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
Upstream-Name: QBlurHash
Upstream-Contact: Joshua Goins <josh@redstrate.com>
Files: .gitignore
Copyright: None
License: CC0-1.0
Files: README.md
Copyright: Joshua Goins <josh@redstrate.com>
License: CC0-1.0

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# SPDX-FileCopyrightText: Joshua Goins <josh@redstrate.com>
# SPDX-License-Identifier: BSD-2-Clause
cmake_minimum_required(VERSION 3.16)
project(QtBlurHash VERSION 1.0.0)
set(KF_MIN_VERSION "6.0.0")
set(QT_MIN_VERSION 6.0)
find_package(ECM ${KF_MIN_VERSION} REQUIRED NO_MODULE)
set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH} ${CMAKE_SOURCE_DIR}/cmake)
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
include(KDEInstallDirs)
include(ECMAddTests)
include(KDECMakeSettings)
include(KDEClangFormat)
include(KDECompilerSettings NO_POLICY_SCOPE)
include(KDEGitCommitHooks)
find_package(Qt6 REQUIRED Core Gui Quick Test)
add_library(blurhash_qt STATIC src/blurhash.cpp src/blurhash.h imageprovider/blurhashimageprovider.h imageprovider/blurhashimageprovider.cpp)
target_include_directories(blurhash_qt PUBLIC src/)
target_link_libraries(blurhash_qt PUBLIC Qt::Core Qt::Gui Qt::Quick)
add_subdirectory(autotests)
file(GLOB_RECURSE ALL_CLANG_FORMAT_SOURCE_FILES src/*.cpp src/*.h)
kde_clang_format(${ALL_CLANG_FORMAT_SOURCE_FILES})
kde_configure_git_pre_commit_hook(CHECKS CLANG_FORMAT)

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MIT License
Copyright (c) <year> <copyright holders>
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
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# QtBlurHash
A modern Qt/C++ implementation of [BlurHash](https://github.com/woltapp/blurhash). In comparison to other implementations, this uses Qt and modern C++ as much as possible. It also comes with a image provider (for use in QML) and a full test suite.
## Usage
Copy the source files under `src/` into your application. The test suite and image provider are optional and located under `autotests/` and `imageprovider/` respectively.
This requires Qt6 and C++20, but it can be made to compile for C++17 with little changes.
## Credits
* [Nheko's Blurhash](https://github.com/Nheko-Reborn/blurhash) as inspiration and the base for the implementation.
* Tobias Fella for the original image provider.

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# SPDX-FileCopyrightText: Joshua Goins <josh@redstrate.com>
# SPDX-License-Identifier: BSD-2-Clause
ecm_add_test(testblurhash.cpp
TEST_NAME testblurhash
LINK_LIBRARIES blurhash_qt Qt::Test
)

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// SPDX-FileCopyrightText: 2024 Joshua Goins <josh@redstrate.com>
// SPDX-License-Identifier: MIT
#include <blurhash.h>
#include <QTest>
class TestBlurHash : public QObject
{
Q_OBJECT
private Q_SLOTS:
void encode83_data();
void encode83();
void decode83_data();
void decode83();
void unpackComponents();
void packComponents();
void decodeMaxAC();
void encodeMaxAC();
void decodeAverageColor_data();
void decodeAverageColor();
void decodeAC();
void encodeAC();
void decodeImage();
void encodeImage();
};
void TestBlurHash::encode83_data()
{
QTest::addColumn<int>("value");
QTest::addColumn<QString>("expected");
QTest::addRow("encoding 1") << 0 << "0";
QTest::addRow("encoding 2") << 21 << "L";
QTest::addRow("encoding 3") << 30 << "U";
QTest::addRow("encoding 4") << 34 << "Y";
QTest::addRow("encoding 5") << 1 << "1";
}
void TestBlurHash::encode83()
{
QFETCH(int, value);
QFETCH(QString, expected);
QCOMPARE(BlurHash::encode83(value), expected);
}
void TestBlurHash::decode83_data()
{
QTest::addColumn<QString>("value");
QTest::addColumn<std::optional<int>>("expected");
// invalid base83 characters
QTest::addRow("decoding 1") << "試し" << std::optional<int>(std::nullopt);
QTest::addRow("decoding 2") << "(" << std::optional<int>(std::nullopt);
QTest::addRow("decoding 3") << "0" << std::optional(0);
QTest::addRow("decoding 4") << "L" << std::optional(21);
QTest::addRow("decoding 5") << "U" << std::optional(30);
QTest::addRow("decoding 6") << "Y" << std::optional(34);
QTest::addRow("decoding 7") << "1" << std::optional(1);
}
void TestBlurHash::decode83()
{
QFETCH(QString, value);
QFETCH(std::optional<int>, expected);
QCOMPARE(BlurHash::decode83(value), expected);
}
void TestBlurHash::unpackComponents()
{
QCOMPARE(BlurHash::unpackComponents(50), BlurHash::Components(6, 6));
}
void TestBlurHash::packComponents()
{
QCOMPARE(BlurHash::packComponents(BlurHash::Components(6, 6)), 50);
}
void TestBlurHash::decodeMaxAC()
{
QCOMPARE(BlurHash::decodeMaxAC(50), 0.307229f);
}
void TestBlurHash::encodeMaxAC()
{
QCOMPARE(BlurHash::encodeMaxAC(0.307229f), 50);
}
void TestBlurHash::decodeAverageColor_data()
{
QTest::addColumn<int>("value");
QTest::addColumn<QColor>("expected");
QTest::addRow("decoding 1") << 12688010 << QColor(0xffc19a8a);
QTest::addRow("decoding 2") << 9934485 << QColor(0xff979695);
QTest::addRow("decoding 3") << 8617624 << QColor(0xff837e98);
QTest::addRow("decoding 4") << 14604757 << QColor(0xffded9d5);
QTest::addRow("decoding 5") << 13742755 << QColor(0xffd1b2a3);
}
void TestBlurHash::decodeAverageColor()
{
QFETCH(int, value);
QFETCH(QColor, expected);
QCOMPARE(BlurHash::decodeAverageColor(value), expected);
}
void TestBlurHash::decodeAC()
{
constexpr auto maxAC = 0.289157f;
QCOMPARE(BlurHash::decodeAC(0, maxAC), QColor::fromRgbF(-0.289063f, -0.289063f, -0.289063f));
}
void TestBlurHash::encodeAC()
{
constexpr auto maxAC = 0.289157f;
QCOMPARE(BlurHash::encodeAC(QColor::fromRgbF(-0.289063f, -0.289063f, -0.289063f), maxAC), 0);
}
void TestBlurHash::decodeImage()
{
const auto image = BlurHash::decode(QStringLiteral("eBB4=;054UK$=402%s%|r^O%06#?*7RijMxGpYMzniVNT@rFN3#=Kt"), QSize(50, 50));
QVERIFY(!image.isNull());
QCOMPARE(image.width(), 50);
QCOMPARE(image.height(), 50);
QCOMPARE(image.pixelColor(0, 0), QColor(0xff005f00));
QCOMPARE(image.pixelColor(30, 30), QColor(0xff99b76d));
}
void TestBlurHash::encodeImage()
{
auto image = QImage(QSize(360, 200), QImage::Format_RGB888);
image.fill(Qt::black);
const auto encodedString = BlurHash::encode(image, 4, 3);
QCOMPARE(encodedString.size(), 28);
QCOMPARE(encodedString, QStringLiteral("L00000fQfQfQfQfQfQfQfQfQfQfQ"));
}
QTEST_GUILESS_MAIN(TestBlurHash)
#include "testblurhash.moc"

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// SPDX-FileCopyrightText: 2024 Joshua Goins <josh@redstrate.com>
// SPDX-License-Identifier: MIT
#include "blurhashimageprovider.h"
#include "blurhash.h"
/*
* Qt unfortunately re-encodes the base83 string in QML.
* The only special ASCII characters used in the blurhash base83 string are:
* #$%*+,-.:;=?@[]^_{|}~
* QUrl::fromPercentEncoding is too greedy, and spits out invalid characters
* for parts of valid base83 like %14.
*/
// clang-format off
static const QMap<QLatin1String, QLatin1String> knownEncodings = {
{QLatin1String("%23A"), QLatin1String(":")},
{QLatin1String("%3F"), QLatin1String("?")},
{QLatin1String("%23"), QLatin1String("#")},
{QLatin1String("%5B"), QLatin1String("[")},
{QLatin1String("%5D"), QLatin1String("]")},
{QLatin1String("%40"), QLatin1String("@")},
{QLatin1String("%24"), QLatin1String("$")},
{QLatin1String("%2A"), QLatin1String("*")},
{QLatin1String("%2B"), QLatin1String("+")},
{QLatin1String("%2C"), QLatin1String(",")},
{QLatin1String("%2D"), QLatin1String("-")},
{QLatin1String("%2E"), QLatin1String(".")},
{QLatin1String("%3D"), QLatin1String("=")},
{QLatin1String("%25"), QLatin1String("%")},
{QLatin1String("%5E"), QLatin1String("^")},
{QLatin1String("%7C"), QLatin1String("|")},
{QLatin1String("%7B"), QLatin1String("{")},
{QLatin1String("%7D"), QLatin1String("}")},
{QLatin1String("%7E"), QLatin1String("~")},
};
// clang-format on
class AsyncImageResponseRunnable : public QObject, public QRunnable
{
Q_OBJECT
Q_SIGNALS:
void done(QImage image);
public:
AsyncImageResponseRunnable(const QString &id, const QSize &requestedSize)
: m_id(id)
, m_requestedSize(requestedSize)
{
if (m_requestedSize.width() == -1)
m_requestedSize.setWidth(64);
if (m_requestedSize.height() == -1)
m_requestedSize.setHeight(64);
}
void run() override
{
if (m_id.isEmpty())
return;
QString decodedId = m_id;
for (auto i = knownEncodings.constBegin(); i != knownEncodings.constEnd(); ++i)
decodedId.replace(i.key(), i.value());
Q_EMIT done(BlurHash::decode(decodedId, m_requestedSize));
}
private:
QString m_id;
QSize m_requestedSize;
};
AsyncImageResponse::AsyncImageResponse(const QString &id, const QSize &requestedSize, QThreadPool *pool)
{
const auto runnable = new AsyncImageResponseRunnable(id, requestedSize);
connect(runnable, &AsyncImageResponseRunnable::done, this, &AsyncImageResponse::handleDone);
pool->start(runnable);
}
void AsyncImageResponse::handleDone(QImage image)
{
m_image = std::move(image);
Q_EMIT finished();
}
QQuickTextureFactory *AsyncImageResponse::textureFactory() const
{
return QQuickTextureFactory::textureFactoryForImage(m_image);
}
QQuickImageResponse *BlurHashImageProvider::requestImageResponse(const QString &id, const QSize &requestedSize)
{
return new AsyncImageResponse(id, requestedSize, &pool);
}
#include "blurhashimageprovider.moc"

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// SPDX-FileCopyrightText: 2024 Joshua Goins <josh@redstrate.com>
// SPDX-License-Identifier: MIT
#pragma once
#include <QQuickAsyncImageProvider>
#include <QThreadPool>
class AsyncImageResponse final : public QQuickImageResponse
{
public:
AsyncImageResponse(const QString &id, const QSize &requestedSize, QThreadPool *pool);
void handleDone(QImage image);
QQuickTextureFactory *textureFactory() const override;
QImage m_image;
};
class BlurHashImageProvider : public QQuickAsyncImageProvider
{
public:
QQuickImageResponse *requestImageResponse(const QString &id, const QSize &requestedSize) override;
private:
QThreadPool pool;
};

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// SPDX-FileCopyrightText: 2024 Joshua Goins <josh@redstrate.com>
// SPDX-License-Identifier: MIT
#include "blurhash.h"
#include <QColorSpace>
// From https://github.com/woltapp/blurhash/blob/master/Algorithm.md#base-83
const static QString b83Characters{QStringLiteral("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~")};
const static auto toLinearSRGB = QColorSpace(QColorSpace::SRgb).transformationToColorSpace(QColorSpace::SRgbLinear);
const static auto fromLinearSRGB = QColorSpace(QColorSpace::SRgbLinear).transformationToColorSpace(QColorSpace::SRgb);
QImage BlurHash::decode(const QString &blurhash, const QSize &size)
{
// 10 is the minimum length of a blurhash string
if (blurhash.length() < 10)
return {};
// First character is the number of components
const auto components83 = decode83(blurhash.first(1));
if (!components83.has_value())
return {};
const auto components = unpackComponents(*components83);
const auto minimumSize = 1 + 1 + 4 + (components.x * components.y - 1) * 2;
if (components.x < 1 || components.y < 1 || blurhash.size() != minimumSize)
return {};
// Second character is the maximum AC component value
const auto maxAC83 = decode83(blurhash.mid(1, 1));
if (!maxAC83.has_value())
return {};
const auto maxAC = decodeMaxAC(*maxAC83);
// Third character onward is the average color of the image
const auto averageColor83 = decode83(blurhash.mid(2, 4));
if (!averageColor83.has_value())
return {};
const auto averageColor = toLinearSRGB.map(decodeAverageColor(*averageColor83));
QList values = {averageColor};
// Iterate through the rest of the string for the color values
// Each AC component is two characters each
for (qsizetype c = 6; c < blurhash.size(); c += 2) {
const auto acComponent83 = decode83(blurhash.mid(c, 2));
if (!acComponent83.has_value())
return {};
values.append(decodeAC(*acComponent83, maxAC));
}
QImage image(size, QImage::Format_RGB888);
image.setColorSpace(QColorSpace::SRgb);
const auto basisX = calculateWeights(size.width(), components.x);
const auto basisY = calculateWeights(size.height(), components.y);
for (int y = 0; y < size.height(); y++) {
for (int x = 0; x < size.width(); x++) {
float linearSumR = 0.0f;
float linearSumG = 0.0f;
float linearSumB = 0.0f;
for (int nx = 0; nx < components.x; nx++) {
for (int ny = 0; ny < components.y; ny++) {
const float basis = basisX[x * components.x + nx] * basisY[y * components.y + ny];
linearSumR += values[nx + ny * components.x].redF() * basis;
linearSumG += values[nx + ny * components.x].greenF() * basis;
linearSumB += values[nx + ny * components.x].blueF() * basis;
}
}
auto linearColor = QColor::fromRgbF(linearSumR, linearSumG, linearSumB);
image.setPixelColor(x, y, fromLinearSRGB.map(linearColor));
}
}
return image;
}
QString BlurHash::encode(const QImage &image, const int componentsX, const int componentsY)
{
Q_ASSERT(componentsX >= 1 && componentsX <= 9);
Q_ASSERT(componentsY >= 1 && componentsY <= 9);
if (image.isNull())
return {};
const auto basisX = calculateWeights(image.width(), componentsX);
const auto basisY = calculateWeights(image.height(), componentsY);
QList<QColor> factors;
factors.resize(componentsX * componentsY);
const float normalizationFactor = 1.0f / static_cast<float>(image.width());
for (int y = 0; y < image.height(); y++) {
for (int x = 0; x < image.width(); x++) {
const QColor srgbColor = image.pixelColor(x, y);
const QColor linearColor = toLinearSRGB.map(srgbColor);
float linearR = linearColor.redF();
float linearG = linearColor.greenF();
float linearB = linearColor.blueF();
linearR *= normalizationFactor;
linearG *= normalizationFactor;
linearB *= normalizationFactor;
for (int ny = 0; ny < componentsY; ny++) {
for (int nx = 0; nx < componentsX; nx++) {
const float basis = basisX[x * componentsX + nx] * basisY[y * componentsY + ny];
float factorR = factors[ny * componentsX + nx].redF();
float factorG = factors[ny * componentsX + nx].greenF();
float factorB = factors[ny * componentsX + nx].blueF();
factors[ny * componentsX + nx] = QColor::fromRgbF(factorR + linearR * basis, factorG + linearG * basis, factorB + linearB * basis);
}
}
}
}
// Scale by normalization. Half the scaling is done in the previous loop to prevent going
// too far outside the float range.
for (qsizetype i = 0; i < factors.size(); i++) {
float normalisation = (i == 0) ? 1 : 2;
float scale = normalisation / static_cast<float>(image.height());
float factorR = factors[i].redF() * scale;
float factorG = factors[i].greenF() * scale;
float factorB = factors[i].blueF() * scale;
factors[i] = QColor::fromRgbF(factorR, factorG, factorB);
}
const auto averageColor = factors.takeFirst();
QString encodedString;
encodedString.append(encode83(packComponents(Components(componentsX, componentsY))).rightJustified(1, QLatin1Char('0')));
float maximumValue;
if (!factors.empty()) {
float actualMaximumValue = 0;
for (auto ac : factors) {
actualMaximumValue = std::max({
std::abs(ac.redF()),
std::abs(ac.greenF()),
std::abs(ac.blueF()),
actualMaximumValue,
});
}
int quantisedMaximumValue = encodeMaxAC(actualMaximumValue);
maximumValue = (static_cast<float>(quantisedMaximumValue) + 1) / 166;
encodedString.append(encode83(quantisedMaximumValue).leftJustified(1, QLatin1Char('0')));
} else {
maximumValue = 1;
encodedString.append(encode83(0).leftJustified(1, QLatin1Char('0')));
}
encodedString.append(encode83(encodeAverageColor(fromLinearSRGB.map(averageColor))).leftJustified(4, QLatin1Char('0')));
for (auto ac : factors)
encodedString.append(encode83(encodeAC(ac, maximumValue)).leftJustified(2, QLatin1Char('0')));
return encodedString;
}
std::optional<int> BlurHash::decode83(const QString &encodedString)
{
int temp = 0;
for (const QChar c : encodedString) {
const auto index = b83Characters.indexOf(c);
if (index == -1)
return std::nullopt;
temp = temp * 83 + static_cast<int>(index);
}
return temp;
}
QString BlurHash::encode83(int value)
{
QString buffer;
do {
buffer += b83Characters[value % 83];
} while ((value = value / 83));
std::ranges::reverse(buffer);
return buffer;
}
BlurHash::Components BlurHash::unpackComponents(const int packedComponents)
{
return {packedComponents % 9 + 1, packedComponents / 9 + 1};
}
int BlurHash::packComponents(const Components &components)
{
return (components.x - 1) + (components.y - 1) * 9;
}
float BlurHash::decodeMaxAC(const int value)
{
return static_cast<float>(value + 1) / 166.f;
}
int BlurHash::encodeMaxAC(const float value)
{
return std::clamp(static_cast<int>(value * 166 - 0.5f), 0, 82);
}
QColor BlurHash::decodeAverageColor(const int encodedValue)
{
const int intR = encodedValue >> 16;
const int intG = (encodedValue >> 8) & 255;
const int intB = encodedValue & 255;
return QColor::fromRgb(intR, intG, intB);
}
int BlurHash::encodeAverageColor(const QColor &averageColor)
{
return (averageColor.red() << 16) + (averageColor.green() << 8) + averageColor.blue();
}
float BlurHash::signPow(const float value, const float exp)
{
return std::copysign(std::pow(std::abs(value), exp), value);
}
QColor BlurHash::decodeAC(const int value, const float maxAC)
{
const auto quantR = value / (19 * 19);
const auto quantG = (value / 19) % 19;
const auto quantB = value % 19;
return QColor::fromRgbF(signPow((static_cast<float>(quantR) - 9) / 9, 2) * maxAC,
signPow((static_cast<float>(quantG) - 9) / 9, 2) * maxAC,
signPow((static_cast<float>(quantB) - 9) / 9, 2) * maxAC);
}
int BlurHash::encodeAC(const QColor value, const float maxAC)
{
const auto quantR = static_cast<int>(std::max(0., std::min(18., std::floor(signPow(value.redF() / maxAC, 0.5) * 9 + 9.5))));
const auto quantG = static_cast<int>(std::max(0., std::min(18., std::floor(signPow(value.greenF() / maxAC, 0.5) * 9 + 9.5))));
const auto quantB = static_cast<int>(std::max(0., std::min(18., std::floor(signPow(value.blueF() / maxAC, 0.5) * 9 + 9.5))));
return quantR * 19 * 19 + quantG * 19 + quantB;
}
QList<float> BlurHash::calculateWeights(const qsizetype dimension, const qsizetype components)
{
QList<float> bases(dimension * components, 0.0f);
const auto scale = static_cast<float>(std::numbers::pi) / static_cast<float>(dimension);
for (qsizetype x = 0; x < dimension; x++) {
for (qsizetype nx = 0; nx < components; nx++) {
bases[x * components + nx] = std::cos(scale * static_cast<float>(nx * x));
}
}
return bases;
}

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// SPDX-FileCopyrightText: 2024 Joshua Goins <josh@redstrate.com>
// SPDX-License-Identifier: MIT
#pragma once
#include <QImage>
/**
* @brief Encodes and decodes image to and from the BlurHash format. See https://blurha.sh/.
*/
class BlurHash
{
public:
/** Decodes the @p blurhash string creating an image of @p size.
* @note Returns a null image if decoding failed.
*/
static QImage decode(const QString &blurhash, const QSize &size);
/** Encodes the @p image and returns a blurhash string.
* @param image A non-null image.
* @param componentsX the number of components X-wise. Must be between 1 and 9.
* @param componentsY the number of components Y-wise. Must be between 1 and 9.
* @note Returns an empty string if it failed to encode the image.
*/
static QString encode(const QImage &image, int componentsX = 4, int componentsY = 4);
protected:
struct Components {
int x, y;
bool operator==(const Components &other) const
{
return x == other.x && y == other.y;
}
};
/**
* @brief Decodes a base 83 string to it's integer value. Returns std::nullopt if there's an invalid character in the blurhash.
*/
static std::optional<int> decode83(const QString &encodedString);
/**
* @brief Encodes an integer to it's base 83 representation.
*/
static QString encode83(int value);
/**
* @brief Unpacks an integer to it's @c Components value.
*/
static Components unpackComponents(int packedComponents);
/**
* @brief Packs @c Components to it's integer representation.
*/
static int packComponents(const Components &components);
/**
* @brief Decodes a encoded max AC component value.
*/
static float decodeMaxAC(int value);
/**
* @brief Encodes the maximum AC component value to an integer repsentation.
*/
static int encodeMaxAC(float value);
/**
* @brief Decodes the average color from the encoded RGB value.
* @note This returns the color as SRGB.
*/
static QColor decodeAverageColor(int encodedValue);
/**
* @brief Encodes the average color into it's integer representation.
*/
static int encodeAverageColor(const QColor &averageColor);
/**
* @brief Calls pow() with @p exp on @p value, while keeping the sign.
*/
static float signPow(float value, float exp);
/**
* @brief Decodes a encoded AC component value.
*/
static QColor decodeAC(int value, float maxAC);
/**
* @brief Encodes the AC component into it's integer representation.
*/
static int encodeAC(QColor value, float maxAC);
/**
* @brief Calculates the weighted sum for @p dimension across @p components.
*/
static QList<float> calculateWeights(qsizetype dimension, qsizetype components);
friend class TestBlurHash;
};