Example of a hybrid C++ and QML application.
The Qt Quick 2 oscilloscope example shows how to combine C++ and QML in an application, as well as showing data that changes realtime.
The interesting thing about this example is combining C++ and QML, so we'll concentrate on that and skip explaining the basic functionality - for more detailed QML example documentation, see Qt Quick 2 Scatter Example .
要运行范例从 Qt Creator ，打开 欢迎 模式，然后选择范例从 范例 。更多信息，拜访 构建和运行范例 .
The item model based proxies are good for simple and/or static graphs, but to achieve best performance when displaying data changing in realtime, the basic proxies should be used. Those are not supported in QML, as the data items they store are not
QObject
s and cannot therefore be directly manipulated from QML code. To overcome this limitation, we implement a simple
DataSource
class in C++ to populate the data proxy of the series.
The
DataSource
class provides three methods that can be called from QML:
public Q_SLOTS: void generateData(int cacheCount, int rowCount, int columnCount, float xMin, float xMax, float yMin, float yMax, float zMin, float zMax); void update(QSurface3DSeries *series);
The first method,
generateData()
, creates a cache of simulated oscilloscope data for us to display. The data is cached in a format accepted by
QSurfaceDataProxy
:
void DataSource::generateData(int cacheCount, int rowCount, int columnCount, float xMin, float xMax, float yMin, float yMax, float zMin, float zMax) { if (!cacheCount || !rowCount || !columnCount) return; clearData(); // Re-create the cache array m_data.resize(cacheCount); for (int i(0); i < cacheCount; i++) { QSurfaceDataArray &array = m_data[i]; array.reserve(rowCount); for (int j(0); j < rowCount; j++) array.append(new QSurfaceDataRow(columnCount)); } float xRange = xMax - xMin; float yRange = yMax - yMin; float zRange = zMax - zMin; int cacheIndexStep = columnCount / cacheCount; float cacheStep = float(cacheIndexStep) * xRange / float(columnCount); // Populate caches for (int i(0); i < cacheCount; i++) { QSurfaceDataArray &cache = m_data[i]; float cacheXAdjustment = cacheStep * i; float cacheIndexAdjustment = cacheIndexStep * i; for (int j(0); j < rowCount; j++) { QSurfaceDataRow &row = *(cache[j]); float rowMod = (float(j)) / float(rowCount); float yRangeMod = yRange * rowMod; float zRangeMod = zRange * rowMod; float z = zRangeMod + zMin; qreal rowColWaveAngleMul = M_PI * M_PI * rowMod; float rowColWaveMul = yRangeMod * 0.2f; for (int k(0); k < columnCount; k++) { float colMod = (float(k)) / float(columnCount); float xRangeMod = xRange * colMod; float x = xRangeMod + xMin + cacheXAdjustment; float colWave = float(qSin((2.0 * M_PI * colMod) - (1.0 / 2.0 * M_PI)) + 1.0); float y = (colWave * ((float(qSin(rowColWaveAngleMul * colMod) + 1.0)))) * rowColWaveMul + QRandomGenerator::global()->bounded(0.15f) * yRangeMod; int index = k + cacheIndexAdjustment; if (index >= columnCount) { // Wrap over index -= columnCount; x -= xRange; } row[index] = QVector3D(x, y, z); } } } }
The second method,
update()
, copies one set of the cached data into another array, which we set to the data proxy of the series by calling
QSurfaceDataProxy::resetArray
(). We reuse the same array if the array dimensions have not changed to minimize overhead:
void DataSource::update(QSurface3DSeries *series) { if (series && m_data.size()) { // Each iteration uses data from a different cached array m_index++; if (m_index > m_data.count() - 1) m_index = 0; QSurfaceDataArray array = m_data.at(m_index); int newRowCount = array.size(); int newColumnCount = array.at(0)->size(); // If the first time or the dimensions of the cache array have changed, // reconstruct the reset array if (!m_resetArray || series->dataProxy()->rowCount() != newRowCount || series->dataProxy()->columnCount() != newColumnCount) { m_resetArray = new QSurfaceDataArray(); m_resetArray->reserve(newRowCount); for (int i(0); i < newRowCount; i++) m_resetArray->append(new QSurfaceDataRow(newColumnCount)); } // Copy items from our cache to the reset array for (int i(0); i < newRowCount; i++) { const QSurfaceDataRow &sourceRow = *(array.at(i)); QSurfaceDataRow &row = *(*m_resetArray)[i]; for (int j(0); j < newColumnCount; j++) row[j].setPosition(sourceRow.at(j).position()); } // Notify the proxy that data has changed series->dataProxy()->resetArray(m_resetArray); } }
注意： Even though we are operating on the array pointer we have previously set to the proxy we still need to call QSurfaceDataProxy::resetArray () after changing the data in it to prompt the graph to render the data.
To be able to access the
DataSource
methods from QML, we need to expose it. We do this by defining a context property in application main:
DataSource dataSource; viewer.rootContext()->setContextProperty("dataSource", &dataSource);
To make it possible to use
QSurface3DSeries
pointers as parameters on the
DataSource
class methods on all environments and builds, we need to make sure the meta type is registered:
Q_DECLARE_METATYPE(QSurface3DSeries *) ... qRegisterMetaType<QSurface3DSeries *>();
In the QML codes, we define a Surface3D graph normally and give it a Surface3DSeries :
Surface3DSeries { id: surfaceSeries drawMode: Surface3DSeries.DrawSurface; flatShadingEnabled: false; meshSmooth: true itemLabelFormat: "@xLabel, @zLabel: @yLabel" itemLabelVisible: false onItemLabelChanged: { if (surfaceSeries.selectedPoint === surfaceSeries.invalidSelectionPosition) selectionText.text = "No selection" else selectionText.text = surfaceSeries.itemLabel } }
One interesting detail is that we don't specify a proxy for the Surface3DSeries we attach to the graph. This makes the series to utilize the default QSurfaceDataProxy .
We also hide the item label with
itemLabelVisible
, since we want to display the selected item information in a
文本
element instead of a floating label above the selection pointer. This is done because the selection pointer moves around a lot as the data changes, which makes the regular selection label difficult to read.
We initialize the
DataSource
cache when the graph is complete by calling a helper function
generateData()
, which calls the method with the same name on the
DataSource
:
Component.onCompleted: mainView.generateData() ... function generateData() { dataSource.generateData(mainView.sampleCache, mainView.sampleRows, mainView.sampleColumns, surfaceGraph.axisX.min, surfaceGraph.axisX.max, surfaceGraph.axisY.min, surfaceGraph.axisY.max, surfaceGraph.axisZ.min, surfaceGraph.axisZ.max) }
To trigger the updates in data, we define a
Timer
item which calls the
update()
method on the
DataSource
at requested intervals. The label update is also triggered on each cycle:
Timer { id: refreshTimer interval: 1000 / frequencySlider.value running: true repeat: true onTriggered: dataSource.update(surfaceSeries) }
Since this application potentially deals with a lot of rapidly changing data, we use direct rendering mode for performance. To enable antialiasing in this mode the surface format of the application window needs to be changed, as the default format used by
QQuickView
doesn't support antialiasing. We use the utility function provided by Qt Data Visualization to change the surface format in
main.cpp
:
viewer.setFormat(QtDataVisualization::qDefaultSurfaceFormat()); ... #include <QtDataVisualization/qutils.h>
On the QML side, direct rendering mode is enabled via renderingMode 特性：
renderingMode: AbstractGraph3D.RenderDirectToBackground
