Accelerating lineseries with OpenGL

Added support for QAbstractSeries::useOpenGL property.
When true, the series in question is drawn on a separate
offscreen buffer using OpenGL and then superimposed on
the chart. Currently this property is only supported
for line and scatter series.

Change-Id: I174fec541f9f3c23464270c1fe08f824af16a0fb
Reviewed-by: Titta Heikkala <titta.heikkala@theqtcompany.com>
Reviewed-by: Tomi Korpipää <tomi.korpipaa@theqtcompany.com>

4 files changed, 347 insertions, 0 deletions

diff --git a/examples/charts/openglseries/datasource.cpp b/examples/charts/openglseries/datasource.cpp
new file mode 100644
index 00000000..64b45405
--- /dev/null
+++ b/examples/charts/openglseries/datasource.cpp
@@ -0,0 +1,118 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd
+** All rights reserved.
+** For any questions to The Qt Company, please use contact form at http://qt.io
+**
+** This file is part of the Qt Charts module.
+**
+** Licensees holding valid commercial license for Qt may use this file in
+** accordance with the Qt License Agreement provided with the Software
+** or, alternatively, in accordance with the terms contained in a written
+** agreement between you and The Qt Company.
+**
+** If you have questions regarding the use of this file, please use
+** contact form at http://qt.io
+**
+****************************************************************************/
+
+#include "datasource.h"
+#include <QtCore/QtMath>
+
+QT_CHARTS_USE_NAMESPACE
+
+DataSource::DataSource(QObject *parent) :
+    QObject(parent),
+    m_index(-1)
+{
+    generateData(0, 0, 0);
+}
+
+void DataSource::update(QAbstractSeries *series, int seriesIndex)
+{
+    if (series) {
+        QXYSeries *xySeries = static_cast<QXYSeries *>(series);
+        const QVector<QVector<QPointF> > &seriesData = m_data.at(seriesIndex);
+        if (seriesIndex == 0)
+            m_index++;
+        if (m_index > seriesData.count() - 1)
+            m_index = 0;
+
+        QVector<QPointF> points = seriesData.at(m_index);
+        // Use replace instead of clear + append, it's optimized for performance
+        xySeries->replace(points);
+    }
+}
+
+void DataSource::handleSceneChanged()
+{
+    m_dataUpdater.start();
+}
+
+void DataSource::updateAllSeries()
+{
+    static int frameCount = 0;
+    static QString labelText = QStringLiteral("FPS: %1");
+
+    for (int i = 0; i < m_seriesList.size(); i++)
+        update(m_seriesList[i], i);
+
+    frameCount++;
+    int elapsed = m_fpsTimer.elapsed();
+    if (elapsed >= 1000) {
+        elapsed = m_fpsTimer.restart();
+        qreal fps = qreal(0.1 * int(10000.0 * (qreal(frameCount) / qreal(elapsed))));
+        m_fpsLabel->setText(labelText.arg(QString::number(fps, 'f', 1)));
+        frameCount = 0;
+    }
+}
+
+void DataSource::startUpdates(const QList<QXYSeries *> &seriesList, QLabel *fpsLabel)
+{
+    m_seriesList = seriesList;
+    m_fpsLabel = fpsLabel;
+
+    m_dataUpdater.setInterval(0);
+    m_dataUpdater.setSingleShot(true);
+    QObject::connect(&m_dataUpdater, &QTimer::timeout,
+                     this, &DataSource::updateAllSeries);
+
+    m_fpsTimer.start();
+    updateAllSeries();
+}
+
+void DataSource::generateData(int seriesCount, int rowCount, int colCount)
+{
+    // Remove previous data
+    foreach (QVector<QVector<QPointF> > seriesData, m_data) {
+        foreach (QVector<QPointF> row, seriesData)
+            row.clear();
+    }
+
+    m_data.clear();
+
+    qreal xAdjustment = 20.0 / (colCount * rowCount);
+    qreal yMultiplier = 3.0 / qreal(seriesCount);
+
+    // Append the new data depending on the type
+    for (int k(0); k < seriesCount; k++) {
+        QVector<QVector<QPointF> > seriesData;
+        qreal height = qreal(k) * (10.0 / qreal(seriesCount)) + 0.3;
+        for (int i(0); i < rowCount; i++) {
+            QVector<QPointF> points;
+            points.reserve(colCount);
+            for (int j(0); j < colCount; j++) {
+                qreal x(0);
+                qreal y(0);
+                // data with sin + random component
+                y = height + (yMultiplier * qSin(3.14159265358979 / 50 * j)
+                              + (yMultiplier * (qreal) rand() / (qreal) RAND_MAX));
+                // 0.000001 added to make values logaxis compatible
+                x = 0.000001 + 20.0 * (qreal(j) / qreal(colCount)) + (xAdjustment * qreal(i));
+                points.append(QPointF(x, y));
+            }
+            seriesData.append(points);
+        }
+        m_data.append(seriesData);
+    }
+}
diff --git a/examples/charts/openglseries/datasource.h b/examples/charts/openglseries/datasource.h
new file mode 100644
index 00000000..295d93a3
--- /dev/null
+++ b/examples/charts/openglseries/datasource.h
@@ -0,0 +1,53 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd
+** All rights reserved.
+** For any questions to The Qt Company, please use contact form at http://qt.io
+**
+** This file is part of the Qt Charts module.
+**
+** Licensees holding valid commercial license for Qt may use this file in
+** accordance with the Qt License Agreement provided with the Software
+** or, alternatively, in accordance with the terms contained in a written
+** agreement between you and The Qt Company.
+**
+** If you have questions regarding the use of this file, please use
+** contact form at http://qt.io
+**
+****************************************************************************/
+
+#ifndef DATASOURCE_H
+#define DATASOURCE_H
+
+#include <QtCore/QObject>
+#include <QtCharts/QXYSeries>
+#include <QtWidgets/QLabel>
+#include <QtCore/QElapsedTimer>
+#include <QtCore/QTimer>
+
+QT_CHARTS_USE_NAMESPACE
+
+class DataSource : public QObject
+{
+    Q_OBJECT
+public:
+    explicit DataSource(QObject *parent = 0);
+
+    void startUpdates(const QList<QXYSeries *> &seriesList, QLabel *fpsLabel);
+
+public slots:
+    void generateData(int seriesCount, int rowCount, int colCount);
+    void update(QAbstractSeries *series, int seriesIndex);
+    void handleSceneChanged();
+    void updateAllSeries();
+
+private:
+    QVector<QVector<QVector<QPointF> > > m_data;
+    int m_index;
+    QList<QXYSeries *> m_seriesList;
+    QLabel *m_fpsLabel;
+    QElapsedTimer m_fpsTimer;
+    QTimer m_dataUpdater;
+};
+
+#endif // DATASOURCE_H
diff --git a/examples/charts/openglseries/main.cpp b/examples/charts/openglseries/main.cpp
new file mode 100644
index 00000000..7b654a5d
--- /dev/null
+++ b/examples/charts/openglseries/main.cpp
@@ -0,0 +1,167 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd
+** All rights reserved.
+** For any questions to The Qt Company, please use contact form at http://qt.io
+**
+** This file is part of the Qt Charts module.
+**
+** Licensees holding valid commercial license for Qt may use this file in
+** accordance with the Qt License Agreement provided with the Software
+** or, alternatively, in accordance with the terms contained in a written
+** agreement between you and The Qt Company.
+**
+** If you have questions regarding the use of this file, please use
+** contact form at http://qt.io
+**
+****************************************************************************/
+
+#include "datasource.h"
+#include <QtWidgets/QApplication>
+#include <QtWidgets/QMainWindow>
+#include <QtCharts/QChartView>
+#include <QtCharts/QLineSeries>
+#include <QtCharts/QScatterSeries>
+#include <QtCharts/QValueAxis>
+#include <QtCharts/QLogValueAxis>
+#include <QtWidgets/QLabel>
+
+// Uncomment to use logarithmic axes instead of regular value axes
+//#define USE_LOG_AXIS
+
+// Uncomment to use regular series instead of OpenGL accelerated series
+//#define DONT_USE_GL_SERIES
+
+// Uncomment to add a simple regular series (thick line) and a matching OpenGL series (thinner line)
+// to verify the series have same visible geometry.
+//#define ADD_SIMPLE_SERIES
+
+QT_CHARTS_USE_NAMESPACE
+
+int main(int argc, char *argv[])
+{
+    QApplication a(argc, argv);
+    QStringList colors;
+    colors << "red" << "blue" << "green" << "black";
+
+    QChart *chart = new QChart();
+    chart->legend()->hide();
+
+#ifdef USE_LOG_AXIS
+    QLogValueAxis *axisX = new QLogValueAxis;
+    QLogValueAxis *axisY = new QLogValueAxis;
+#else
+    QValueAxis *axisX = new QValueAxis;
+    QValueAxis *axisY = new QValueAxis;
+#endif
+
+    chart->addAxis(axisX, Qt::AlignBottom);
+    chart->addAxis(axisY, Qt::AlignLeft);
+
+    const int seriesCount = 10;
+#ifdef DONT_USE_GL_SERIES
+    const int pointCount = 100;
+    chart->setTitle("Unaccelerated Series");
+#else
+    const int pointCount = 10000;
+    chart->setTitle("OpenGL Accelerated Series");
+#endif
+
+    QList<QXYSeries *> seriesList;
+    for (int i = 0; i < seriesCount; i++) {
+        QXYSeries *series = 0;
+        int colorIndex = i % colors.size();
+        if (i % 2) {
+            series = new QScatterSeries;
+            QScatterSeries *scatter = static_cast<QScatterSeries *>(series);
+            scatter->setColor(QColor(colors.at(colorIndex)));
+            scatter->setMarkerSize(qreal(colorIndex + 2) / 2.0);
+            // Scatter pen doesn't have affect in OpenGL drawing, but if you disable OpenGL drawing
+            // this makes the marker border visible and gives comparable marker size to OpenGL
+            // scatter points.
+            scatter->setPen(QPen("black"));
+        } else {
+            series = new QLineSeries;
+            series->setPen(QPen(QBrush(QColor(colors.at(colorIndex))),
+                                qreal(colorIndex + 2) / 2.0));
+        }
+        seriesList.append(series);
+#ifdef DONT_USE_GL_SERIES
+        series->setUseOpenGL(false);
+#else
+        //![1]
+        series->setUseOpenGL(true);
+        //![1]
+#endif
+        chart->addSeries(series);
+        series->attachAxis(axisX);
+        series->attachAxis(axisY);
+    }
+
+    if (axisX->type() == QAbstractAxis::AxisTypeLogValue)
+        axisX->setRange(0.1, 20.0);
+    else
+        axisX->setRange(0, 20.0);
+
+    if (axisY->type() == QAbstractAxis::AxisTypeLogValue)
+        axisY->setRange(0.1, 10.0);
+    else
+        axisY->setRange(0, 10.0);
+
+#ifdef ADD_SIMPLE_SERIES
+    QLineSeries *simpleRasterSeries = new QLineSeries;
+    *simpleRasterSeries << QPointF(0.001, 0.001)
+                 << QPointF(2.5, 8.0)
+                 << QPointF(5.0, 4.0)
+                 << QPointF(7.5, 9.0)
+                 << QPointF(10.0, 0.001)
+                 << QPointF(12.5, 2.0)
+                 << QPointF(15.0, 1.0)
+                 << QPointF(17.5, 6.0)
+                 << QPointF(20.0, 10.0);
+    simpleRasterSeries->setUseOpenGL(false);
+    simpleRasterSeries->setPen(QPen(QBrush("magenta"), 8));
+    chart->addSeries(simpleRasterSeries);
+    simpleRasterSeries->attachAxis(axisX);
+    simpleRasterSeries->attachAxis(axisY);
+
+    QLineSeries *simpleGLSeries = new QLineSeries;
+    simpleGLSeries->setUseOpenGL(true);
+    simpleGLSeries->setPen(QPen(QBrush("black"), 2));
+    simpleGLSeries->replace(simpleRasterSeries->points());
+    chart->addSeries(simpleGLSeries);
+    simpleGLSeries->attachAxis(axisX);
+    simpleGLSeries->attachAxis(axisY);
+#endif
+
+    QChartView *chartView = new QChartView(chart);
+
+    QMainWindow window;
+    window.setCentralWidget(chartView);
+    window.resize(600, 400);
+    window.show();
+
+    DataSource dataSource;
+    dataSource.generateData(seriesCount, 10, pointCount);
+
+    QLabel *fpsLabel = new QLabel(&window);
+    QLabel *countLabel = new QLabel(&window);
+    QString countText = QStringLiteral("Total point count: %1");
+    countLabel->setText(countText.arg(pointCount * seriesCount));
+    countLabel->resize(window.width(), countLabel->height());
+    fpsLabel->move(10,2);
+    fpsLabel->raise();
+    fpsLabel->show();
+    countLabel->move(10, 14);
+    fpsLabel->raise();
+    countLabel->show();
+
+    // We can get more than one changed event per frame, so do async update.
+    // This also allows the application to be responsive.
+    QObject::connect(chart->scene(), &QGraphicsScene::changed,
+                     &dataSource, &DataSource::handleSceneChanged);
+
+    dataSource.startUpdates(seriesList, fpsLabel);
+
+    return a.exec();
+}
diff --git a/examples/charts/openglseries/openglseries.pro b/examples/charts/openglseries/openglseries.pro
new file mode 100644
index 00000000..0ae11595
--- /dev/null
+++ b/examples/charts/openglseries/openglseries.pro
@@ -0,0 +1,9 @@
+!include( ../examples.pri ) {
+    error( "Couldn't find the examples.pri file!" )
+}
+
+TARGET = openglseries
+SOURCES += main.cpp \
+    datasource.cpp
+HEADERS += datasource.h
+