创建散点图

包含三个数据序列的散点图截图：蓝色圆点（散点1）、绿色方块（散点2）和橙色星号（散点3）

要创建散点图，需要一个 QScatterSeries 实例。在此，我们创建一个散点系列实例，并设置散点的外线类型和宽度。

auto series0 = new QScatterSeries;
series0->setName("scatter1");
series0->setMarkerShape(QScatterSeries::MarkerShapeCircle);
series0->setMarkerSize(15.0);

auto series1 = new QScatterSeries;
series1->setName("scatter2");
series1->setMarkerShape(QScatterSeries::MarkerShapeRectangle);
series1->setMarkerSize(20.0);

auto series2 = new QScatterSeries;
series2->setName("scatter3");
series2->setMarkerShape(QScatterSeries::MarkerShapeRectangle);
series2->setMarkerSize(30.0);

我们将要显示的数据添加进去。可以使用 append() 成员函数，也可以使用流运算符。

series0->append(0, 6);
series0->append(2, 4);
series0->append(3, 8);
series0->append(7, 4);
series0->append(10, 5);

*series1 << QPointF(1, 1) << QPointF(3, 3) << QPointF(7, 6) << QPointF(8, 3) << QPointF(10, 2);
*series2 << QPointF(1, 5) << QPointF(4, 6) << QPointF(6, 3) << QPointF(9, 5);

我们可以将散点系列的画笔定义为一张图片。此处使用的图片是一颗使用QPainterPath 生成的星星。

QPainterPath starPath;
starPath.moveTo(28, 15);
for (int i = 1; i < 5; ++i) {
    starPath.lineTo(14 + 14 * qCos(0.8 * i * M_PI),
                    15 + 14 * qSin(0.8 * i * M_PI));
}
starPath.closeSubpath();

QImage star(30, 30, QImage::Format_ARGB32);
star.fill(Qt::transparent);

QPainter painter(&star);
painter.setRenderHint(QPainter::Antialiasing);
painter.setPen(QRgb(0xf6a625));
painter.setBrush(painter.pen().color());
painter.drawPath(starPath);

series2->setBrush(star);
series2->setPen(QColor(Qt::transparent));

最后，我们启用抗锯齿、设置图表标题，并将散点系列添加到图表中。同时，我们禁用了投影效果，因为在仅显示图表视图的应用程序中，该效果会显得不协调。

auto chart = new QChart;
chart->addSeries(series0);
chart->addSeries(series1);
chart->addSeries(series2);

chart->setTitle("Simple Scatter Chart");
chart->createDefaultAxes();
chart->setDropShadowEnabled(false);

我们还可以将散点图的点用作图例标记。

chart->legend()->setMarkerShape(QLegend::MarkerShapeFromSeries);

图表现已准备就绪，可以显示了。

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