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