c++ - 问题覆盖绘制曲线的 c++ 类

Question

我正在尝试实现一个程序，当用户点击屏幕时，该程序会点对点绘制线条。我有一个 Polyline 类，它是 Freeform 类的子类，而 Freeform 类又是 Curve 类的子类。 Curve 父类(super class)的 draw 方法通常调用 getPoint，它将在该特定点获得曲线的加权点。但是，对于 Polyline 的 draw 方法，我试图覆盖曲线类以仅获取用户单击的点(如您所见，Polyline 类的 draw 方法从不调用 getPoint)。但是，当我调试代码时，我发现在尝试绘制多段线时仍在调用 getPoint。有什么建议吗？

class Curve {

public:
    virtual float2 getPoint(float t)=0;

    void draw(){

        glBegin(GL_LINE_STRIP);
        for (float i = 0; i < 1; i+=.01) {
            float2 point = getPoint(i);
            float x = point.x;
            float y = point.y;
            glVertex2d(x, y);

        }
        glEnd();
        }; 
    };

class Freeform : public Curve
{
protected:
    std::vector<float2> controlPoints;

public:
    virtual float2 getPoint(float t)=0;
    virtual void addControlPoint(float2 p)
    {
        controlPoints.push_back(p);
    }
    void drawControlPoints(){
        glBegin(GL_POINTS);
        for (float i = 0; i < controlPoints.size(); i++) {
            float2 point = controlPoints.at(i);
            float x = point.x;
            float y = point.y;
            glVertex2d(x, y);

        }
        glEnd();// draw points at control points
    }
};

class Polyline : public Freeform {
public:
    float2 getPoint(float t) {
        return float2(0.0, 0.0);
    }
    //we add a control point (in this case, control point is where mouse is clicked)
    void addControlPoint(float2 p)
    {
        controlPoints.push_back(p);
    }
    //trying to override Curve draw method
    void draw(){
        glBegin(GL_LINE_STRIP);
            for (float i = 0; i < controlPoints.size(); i++) {
            float2 point = controlPoints.at(i);
            float x = point.x;
            float y = point.y;
            glVertex2d(x, y);
        }
        glEnd();
    };
};

Answer 1

//trying to override Curve draw method

上面的评论几乎说明了一切；您正在“尝试”覆盖void Curve::draw ()，但由于成员函数之前未声明，因此未能成功虚拟。

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解决方案

• 将 void Curve::draw () 声明为 virtual。
• 如果c++11或稍后，查看(并使用)关键字 override .