qt - 在 QWT Plot 中更改轴刻度和标签以在毫米和英寸之间切换

Question

我想要的是切换轴标签和刻度以匹配最好的显示英寸和毫米而不改变曲线点。我创建了一个自定义 QwtScaleDraw 并覆盖了 label() 方法，但这不会改变刻度。

class QwtMyScaleDraw : public QwtScaleDraw {
public:
    QwtMyScaleDraw() : QwtScaleDraw() {
    }
protected:
    QwtText label(double value) const {
           // global conversion routine that creates a display string either as millimeter or inch
           return ConvertToString(value, ConversionFromMillimeter);
    }
};

您可以在下图中看到此行为：

左边的比例是原始比例，中间的比例是我的自定义标签，右边是所需的比例。

在不使用手动转换值再次添加整个曲线的情况下获得所需结果的最佳方法是什么？

Answer 1

在 qwt 库作者的帮助下，我找到了解决方案。答案是派生自QwtLinearScaleEngine类和重载autoScale和divideScale方法。

在我的实现中，可以选择任何转换因子（默认为 1 = 无转换）。这是我的代码：

class QwtUnitScaleDraw : public QwtScaleDraw {
public:
    QwtUnitScaleDraw(double ConversionFactor = 1.0) : QwtScaleDraw(), _ConversionFactor(ConversionFactor) {
    }
protected:
    QwtText label(double value) const {
        return QwtScaleDraw::label(value * _ConversionFactor);
    }
protected:
    double _ConversionFactor;
};

class QwtUnitScaleEngine: public QwtLinearScaleEngine {
public:
    QwtUnitScaleEngine(double ConversionFactor = 1.0) : QwtLinearScaleEngine(10), _ConversionFactor(ConversionFactor) {
    }

    void autoScale(int maxSteps, double &x1, double &x2, double &stepSize) const {
        x1 *= _ConversionFactor;
        x2 *= _ConversionFactor;
        stepSize *= _ConversionFactor;
        QwtLinearScaleEngine::autoScale(maxSteps, x1, x2, stepSize);
        x1 /= _ConversionFactor;
        x2 /= _ConversionFactor;
        stepSize /= _ConversionFactor;

    }

    QwtScaleDiv divideScale(double x1, double x2, int numMajorSteps, int numMinorSteps, double stepSize = 0.0) const {
        x1 *= _ConversionFactor;
        x2 *= _ConversionFactor;
        stepSize *= _ConversionFactor;

        QwtScaleDiv Div = QwtLinearScaleEngine::divideScale(x1, x2, numMajorSteps, numMinorSteps, stepSize);

        QList<double> Ticks[QwtScaleDiv::NTickTypes];

        Ticks[QwtScaleDiv::MajorTick] = Div.ticks(QwtScaleDiv::MajorTick);
        for (unsigned int i = 0; i < Ticks[QwtScaleDiv::MajorTick].count(); i++) {
            Ticks[QwtScaleDiv::MajorTick][i] /= _ConversionFactor;
        }
        Ticks[QwtScaleDiv::MediumTick] = Div.ticks(QwtScaleDiv::MediumTick);
        for (unsigned int i = 0; i < Ticks[QwtScaleDiv::MediumTick].count(); i++) {
            Ticks[QwtScaleDiv::MediumTick][i] /= _ConversionFactor;
        }
        Ticks[QwtScaleDiv::MinorTick] = Div.ticks(QwtScaleDiv::MinorTick);
        for (unsigned int i = 0; i < Ticks[QwtScaleDiv::MinorTick].count(); i++) {
            Ticks[QwtScaleDiv::MinorTick][i] /= _ConversionFactor;
        }

        return QwtScaleDiv(QwtInterval(x1 / _ConversionFactor, x2 / _ConversionFactor), Ticks);
    }
protected:
    double _ConversionFactor;
};