line()

void line(InputOutputArray img, Point pt1, Point pt2, const Scalar& color,
                     int thickness = 1, int lineType = LINE_8, int shift = 0);

The function line draws the line segment between pt1 and pt2 points in the image. The line is clipped by the image boundaries. For non-antialiased lines with integer coordinates, the 8-connected or 4-connected Bresenham algorithm is used. Thick lines are drawn with rounding endings. Antialiased lines are drawn using Gaussian filtering.

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circle()

void circle( InputOutputArray _img, Point center, int radius,
             const Scalar& color, int thickness, int line_type, int shift )

The function circle draws a simple or filled circle with a given center and radius.
@param thickness Thickness of the circle outline, if positive. Negative thickness means that a filled circle is to be drawn.

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rectangle()

void rectangle(InputOutputArray img, Point pt1, Point pt2,
                          const Scalar& color, int thickness = 1,
                          int lineType = LINE_8, int shift = 0);

@param pt1 Vertex of the rectangle.
@param pt2 Vertex of the rectangle opposite to pt1 .

void rectangle(CV_IN_OUT Mat& img, Rect rec,
                          const Scalar& color, int thickness = 1,
                          int lineType = LINE_8, int shift = 0);

use rec parameter as alternative specification of the drawn rectangle: r.tl() and r.br()-Point(1,1) are opposite corners

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ellipse()

void ellipse(InputOutputArray img, Point center, Size axes,
                        double angle, double startAngle, double endAngle,
                        const Scalar& color, int thickness = 1,
                        int lineType = LINE_8, int shift = 0);

@param center Center of the ellipse.
@param axes Half of the size of the ellipse main axes.
@param angle Ellipse rotation angle in degrees.
@param startAngle Starting angle of the elliptic arc in degrees.
@param endAngle Ending angle of the elliptic arc in degrees.

angle参数为整个椭圆的角度
startAngle、endAngle为始末位置

void ellipse(InputOutputArray img, const RotatedRect& box, const Scalar& color,
                        int thickness = 1, int lineType = LINE_8);

@param box Alternative ellipse representation via RotatedRect. This means that the function draws
an ellipse inscribed in the rotated rectangle.

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polyline()

void polylines(InputOutputArray img, InputArrayOfArrays pts,
                            bool isClosed, const Scalar& color,
                            int thickness = 1, int lineType = LINE_8, int shift = 0 );

void polylines(Mat& img, const Point* const* pts, const int* npts,
                          int ncontours, bool isClosed, const Scalar& color,
                          int thickness = 1, int lineType = LINE_8, int shift = 0 );

@param pts Array of polygonal curves.
@param isClosed Flag indicating whether the drawn polylines are closed or not. If they are closed,
the function draws a line from the last vertex of each curve to its first vertex.

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LineTypes:

enum LineTypes {
    FILLED  = -1,
    LINE_4  = 4, //!< 4-connected line
    LINE_8  = 8, //!< 8-connected line
    LINE_AA = 16 //!< antialiased line
};