使用qt绘制一个对数坐标系

以下是使用 Qt 绘制对数坐标系的示例代码：

#include <QPainter>
#include <QPointF>
#include <QVector>

// 绘制对数坐标系
void drawLogarithmicCoordinateSystem(QPainter *painter, const QRectF &rect, qreal xMin, qreal xMax, qreal yMin, qreal yMax)
{
    // 计算对数坐标系中坐标轴的起始、结束位置
    QPointF startPoint(rect.left(), rect.bottom());
    QPointF endPoint(rect.right(), rect.bottom());
    QPointF yStartPoint(rect.left(), rect.bottom());
    QPointF yEndPoint(rect.left(), rect.top());

    qreal xDiff = xMax - xMin;
    qreal yDiff = yMax - yMin;

    if (xDiff > 0 && yDiff > 0) {
        qreal xLogDiff = log10(xMax) - log10(xMin);
        qreal yLogDiff = log10(yMax) - log10(yMin);

        // 根据对数坐标系中的坐标计算出实际坐标系中的坐标
        auto getPoint = [=](qreal x, qreal y) {
            qreal realX = rect.left() + (log10(x) - log10(xMin)) / xLogDiff * rect.width();
            qreal realY = rect.bottom() - (log10(y) - log10(yMin)) / yLogDiff * rect.height();
            return QPointF(realX, realY);
        };

        // 绘制横轴
        painter->drawLine(getPoint(xMin, yMin), getPoint(xMax, yMin));

        // 绘制纵轴
        painter->drawLine(getPoint(xMin, yMin), getPoint(xMin, yMax));

        // 绘制横轴刻度线和刻度值
        QVector<QPointF> xTickPoints;
        qreal xTickStep = pow(10, floor(log10(xMin)));
        qreal xTickStart = ceil(xMin / xTickStep) * xTickStep;
        qreal xTickEnd = xMax;
        for (qreal x = xTickStart; x <= xTickEnd; x += xTickStep) {
            xTickPoints.append(getPoint(x, yMin));
            painter->drawLine(getPoint(x, yMin), getPoint(x, yMin - 5));
            painter->drawText(getPoint(x, yMin + 10), QString::number(x));
        }

        // 绘制纵轴刻度线和刻度值
        QVector<QPointF> yTickPoints;
        qreal yTickStep = pow(10, floor(log10(yMin)));
        qreal yTickStart = ceil(yMin / yTickStep) * yTickStep;
        qreal yTickEnd = yMax;
        for (qreal y = yTickStart; y <= yTickEnd; y += yTickStep) {
            yTickPoints.append(getPoint(xMin, y));
            painter->drawLine(getPoint(xMin, y), getPoint(xMin - 5, y));
            painter->drawText(getPoint(xMin - 30, y + 5), QString::number(y));
        }

        // 绘制横轴标签
        painter->drawText(getPoint(xMax, yMin + 30), "X");

        // 绘制纵轴标签
        painter->save();
        painter->translate(getPoint(xMin, yMax));
        painter->rotate(-90);
        painter->drawText(QPointF(0, 0), "Y");
        painter->restore();

        // 绘制网格线
        for (const QPointF &point : xTickPoints) {
            painter->drawLine(point, getPoint(xMin, point.y()));
        }
        for (const QPointF &point : yTickPoints) {
            painter->drawLine(point, getPoint(point.x(), yMin));
        }
    }
}

在 Qt 中，我们可以使用 `QPainter` 绘制任何形状。在绘制对数坐标系时，我们需要计算出对数坐标系中坐标轴的起始、结束位置，并根据对数坐标系中的坐标计算出实际坐标系中的坐标。然后我们就可以绘制坐标轴、刻度线、刻度值、标签、网格线等元素了。