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* Copyright 2012 Canonical Ltd.
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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; version 3.
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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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* Author: Florian Boucault <florian.boucault@canonical.com>
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#include <QtQml/QQmlContext>
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#include <QtQml/QQmlFile>
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#include <QtCore/QFileInfo>
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#include <QtCore/QDir>
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#include <QtCore/QRegularExpression>
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#include <QtCore/qmath.h>
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#include <QtGui/QGuiApplication>
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#include <QtGui/QScreen>
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#define ENV_GRID_UNIT_PX "GRID_UNIT_PX"
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#define DEFAULT_GRID_UNIT_PX 8
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static float getenvFloat(const char* name, float defaultValue)
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QByteArray stringValue = qgetenv(name);
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float value = stringValue.toFloat(&ok);
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return ok ? value : defaultValue;
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\inqmlmodule Ubuntu.Components 1.1
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\ingroup resolution-independence
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\brief Units of measurement for sizes, spacing, margin, etc.
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Units provides facilities for measuring UI elements in a variety
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of units other than just pixels.
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A global instance of Units is exposed as the \b{units} context property.
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import Ubuntu.Components 1.2
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\sa {Resolution Independence}
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* Note on the interaction between GRID_UNIT_PX and QT_DEVICE_PIXEL_RATIO
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* In Qt5.4 there is a single means to scale the UI: the QT_DEVICE_PIXEL_RATIO environment
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* variable. This accepts only integer values, thus allowing a x2 or x3 scaling of any
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* Qt-based UI, that includes QWidget as well as any QML UI.
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* Setting QT_DEVICE_PIXEL_RATIO=2 implies one density-independent pixel corresponds to 2
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* physical pixels. Developers describe their UI in terms of density-independent pixels.
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* Qt scales accordingly.
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* The Ubuntu UI Toolkit has solved the scaling problem with the GRID_UNIT_PX variable.
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* It offers more flexibility, but only scales QML applications written to use the UITK
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* (since it uses this Units class) as it is built on top of QML.
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* There are additional areas in Qt where QT_DEVICE_PIXEL_RATIO causes correct scaling which
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* GRID_UNIT_PX cannot, for example:
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* 1. cacheBuffer for ListView/GridViews - specified in density-independent pixels
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* 2. gesture recognition matches what is on screen better, as it is density-independent
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* In order to get the best of both worlds, Ubuntu will set both GRID_UNIT_PX and
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* QT_DEVICE_PIXEL_RATIO. Thus all Qt apps will scale reasonably well, with UITK-based apps
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* scaling perfectly for any desired scale (i.e. non-integer scales).
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* However UITK developers can just use this Units class as usual, and will be almost totally
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* isolated from Qt's own scaling concept.
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UCUnits::UCUnits(QObject *parent) :
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m_devicePixelRatio(qGuiApp->devicePixelRatio())
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// If GRID_UNIT_PX set, always use it. If not, 1GU := DEFAULT_GRID_UNIT_PX * m_devicePixelRatio
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if (qEnvironmentVariableIsSet(ENV_GRID_UNIT_PX)) {
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m_gridUnit = getenvFloat(ENV_GRID_UNIT_PX, DEFAULT_GRID_UNIT_PX);
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m_gridUnit = DEFAULT_GRID_UNIT_PX * m_devicePixelRatio;
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\qmlproperty real Units::gridUnit
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The number of pixels 1 grid unit corresponds to.
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float UCUnits::gridUnit()
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void UCUnits::setGridUnit(float gridUnit)
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m_gridUnit = gridUnit;
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Q_EMIT gridUnitChanged();
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\qmlmethod real Units::dp(real value)
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Returns the number of pixels \a value density independent pixels correspond to.
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// Density-independent pixels (and not physical pixels) because Qt sizes in terms of density-independent pixels.
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float UCUnits::dp(float value)
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const float ratio = m_gridUnit / DEFAULT_GRID_UNIT_PX;
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// for values under 2dp, return only multiples of the value
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return qRound(value * qFloor(ratio)) / m_devicePixelRatio;
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return qRound(value * ratio) / m_devicePixelRatio;
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\qmlmethod real Units::gu(real value)
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Returns the number of pixels \a value grid units correspond to.
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// Density-independent pixels (and not physical pixels) because Qt sizes in terms of density-independent pixels.
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float UCUnits::gu(float value)
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return qRound(value * m_gridUnit) / m_devicePixelRatio;
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QString UCUnits::resolveResource(const QUrl& url)
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QString path = QQmlFile::urlToLocalFileOrQrc(url);
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if (path.isEmpty()) {
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QFileInfo fileInfo(path);
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if (fileInfo.exists() && !fileInfo.isFile()) {
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QString prefix = fileInfo.dir().absolutePath() + QDir::separator() + fileInfo.baseName();
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QString suffix = "." + fileInfo.completeSuffix();
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/* Use file with expected grid unit suffix if it exists.
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For example, if m_gridUnit = 10, look for resource@10.png.
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path = prefix + suffixForGridUnit(m_gridUnit) + suffix;
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if (QFile::exists(path)) {
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return QString("1") + "/" + path;
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/* No file with expected grid unit suffix exists.
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List all the files of the form fileBaseName@[0-9]*.fileSuffix and select
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the most appropriate one privileging downscaling high resolution assets
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over upscaling low resolution assets.
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The most appropriate file has a grid unit suffix greater than the target
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grid unit (m_gridUnit) yet as small as possible.
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If no file with a grid unit suffix greater than the target grid unit
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exists, then select one with a grid unit suffix as close as possible to
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the target grid unit.
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For example, if m_gridUnit = 10 and the available files are
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resource@9.png, resource@14.png and resource@18.png, the most appropriate
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file would be resource@14.png since it is above 10 and smaller
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than resource@18.png.
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QStringList nameFilters;
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nameFilters << fileInfo.baseName() + "@[0-9]*" + suffix;
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QStringList files = fileInfo.dir().entryList(nameFilters, QDir::Files);
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if (!files.empty()) {
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float selectedGridUnitSuffix = gridUnitSuffixFromFileName(files.first());
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Q_FOREACH (const QString& fileName, files) {
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float gridUnitSuffix = gridUnitSuffixFromFileName(fileName);
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if ((selectedGridUnitSuffix >= m_gridUnit && gridUnitSuffix >= m_gridUnit && gridUnitSuffix < selectedGridUnitSuffix)
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|| (selectedGridUnitSuffix < m_gridUnit && gridUnitSuffix > selectedGridUnitSuffix)) {
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selectedGridUnitSuffix = gridUnitSuffix;
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path = prefix + suffixForGridUnit(selectedGridUnitSuffix) + suffix;
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float scaleFactor = m_gridUnit / selectedGridUnitSuffix;
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return QString::number(scaleFactor) + "/" + path;
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path = prefix + suffix;
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if (QFile::exists(path)) {
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return QString("1") + "/" + path;
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QString UCUnits::suffixForGridUnit(float gridUnit)
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return "@" + QString::number(gridUnit);
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float UCUnits::gridUnitSuffixFromFileName(const QString& fileName)
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QRegularExpression re("^.*@([0-9]*).*$");
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QRegularExpressionMatch match = re.match(fileName);
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if (match.hasMatch()) {
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return match.captured(1).toFloat();
added
removed
src/plugin/libreofficetoolkit-qml-plugin/ucunits.cpp
