- Qt 5.15
- Qt Charts
- Qt Charts Examples
- Qml Oscilloscope
- Qt Charts | Commercial or GPLv3

# 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);
     }

Example project @ code.qt.io