Qt 5.7 | Qt Charts | Qml Oscilloscope

Qt 5.7.1 Reference Documentation

# Qml Oscilloscope

The oscilloscope application demonstrates how to use the Qt Charts QML API to implement an application with strict performance requirements. The application uses generated data with configurable characteristics to mimic a simple oscilloscope user interface.

To get information about actual rendering speed shown in the application output console, you can set QSG_RENDER_TIMING = 1 to your run environment settings. To do so go to Projects - Run - Run environment in Qt Creator and select Add. Then you can experiment with the different configurable options of the example application to find the configuration that gives you the best performance in your environment.

The application window is shared by control and scope views:

      Item {
          id: main
          width: 600
          height: 400

          ControlPanel {
              id: controlPanel
              anchors.top: parent.top
              anchors.topMargin: 10
              anchors.bottom: parent.bottom
              anchors.left: parent.left
              anchors.leftMargin: 10
          ...
          ScopeView {
              id: scopeView
              anchors.top: parent.top
              anchors.bottom: parent.bottom
              anchors.right: parent.right
              anchors.left: controlPanel.right
              height: main.height
          }

ControlView implements the buttons used for configuring. ScopeView uses a ChartView to show a chart with two line series:

      ChartView {
          id: chartView
          animationOptions: ChartView.NoAnimation
          theme: ChartView.ChartThemeDark
          property bool openGL: true
          onOpenGLChanged: {
              series("signal 1").useOpenGL = openGL;
              series("signal 2").useOpenGL = openGL;
          }

          ValueAxis {
              id: axisY1
              min: -1
              max: 4
          }

          ValueAxis {
              id: axisY2
              min: -10
              max: 5
          }

          ValueAxis {
              id: axisX
              min: 0
              max: 1024
          }

          LineSeries {
              id: lineSeries1
              name: "signal 1"
              axisX: axisX
              axisY: axisY1
              useOpenGL: chartView.openGL
          }
          LineSeries {
              id: lineSeries2
              name: "signal 2"
              axisX: axisX
              axisYRight: axisY2
              useOpenGL: chartView.openGL
          }
          ...

The data of the line series is updated with a QML timer. In a real life application the updating could be triggered with a signal from Qt C++ code.

      Timer {
          id: refreshTimer
          interval: 1 / 60 * 1000 // 60 Hz
          running: true
          repeat: true
          onTriggered: {
              dataSource.update(chartView.series(0));
              dataSource.update(chartView.series(1));
          }
      }

The oscilloscope also allows you to switch the type of the series used for visualizing the signal sources. This is implemented by dynamically destroying and creating series:

      function changeSeriesType(type) {
          chartView.removeAllSeries();

          // Create two new series of the correct type. Axis x is the same for both of the series,
          // but the series have their own y-axes to make it possible to control the y-offset
          // of the "signal sources".
          if (type == "line") {
              var series1 = chartView.createSeries(ChartView.SeriesTypeLine, "signal 1",
                                                   axisX, axisY1);
              series1.useOpenGL = chartView.openGL

              var series2 = chartView.createSeries(ChartView.SeriesTypeLine, "signal 2",
                                                   axisX, axisY2);
              series2.useOpenGL = chartView.openGL
          } else {
              var series1 = chartView.createSeries(ChartView.SeriesTypeScatter, "signal 1",
                                                   axisX, axisY1);
              series1.markerSize = 2;
              series1.borderColor = "transparent";
              series1.useOpenGL = chartView.openGL

              var series2 = chartView.createSeries(ChartView.SeriesTypeScatter, "signal 2",
                                                   axisX, axisY2);
              series2.markerSize = 2;
              series2.borderColor = "transparent";
              series2.useOpenGL = chartView.openGL
          }
      }

      function createAxis(min, max) {
          // The following creates a ValueAxis object that can be then set as a x or y axis for a series
          return Qt.createQmlObject("import QtQuick 2.0; import QtCharts 2.0; ValueAxis { min: "
                                    + min + "; max: " + max + " }", chartView);
      }

Files:

- qmloscilloscope/datasource.cpp
- qmloscilloscope/datasource.h
- qmloscilloscope/qml/qmloscilloscope/ControlPanel.qml
- qmloscilloscope/qml/qmloscilloscope/MultiButton.qml
- qmloscilloscope/qml/qmloscilloscope/ScopeView.qml
- qmloscilloscope/qml/qmloscilloscope/main.qml
- qmloscilloscope/main.cpp
- qmloscilloscope/qmloscilloscope.pro
- qmloscilloscope/resources.qrc