Qml Oscilloscope

The example shows how to implement application with strict performance requirements using the Qt Charts QML API.

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.

Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

Creating Views

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

          onOpenGLSupportedChanged: {
              if (!openGLSupported) {
                  controlPanel.openGLButton.enabled = false
                  controlPanel.openGLButton.currentSelection = 0
              }
          }
      }

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
      property bool openGLSupported: true
      onOpenGLChanged: {
          if (openGLSupported) {
              series("signal 1").useOpenGL = openGL;
              series("signal 2").useOpenGL = openGL;
          }
      }
      Component.onCompleted: {
          if (!series("signal 1").useOpenGL) {
              openGLSupported = false
              openGL = false
          }
      }

      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:

Contents

Qml Oscilloscope

Running the Example

Creating Views