1、线段的绘制

OpenCvSharp提供Cv2.Line方法，使用该方法可以绘制各种线段，Cv2.Line方法如下：

public static void Line(InputOutputArray img, Point pt1, Point pt2, Scalar color, int thickness = 1, LineTypes lineType = LineTypes.Link8, int shift = 0)

说明：

摘要:
    Draws a line segment connecting two points

参数:
  img:
    The image.

  pt1:
    First point of the line segment.

  pt2:
    Second point of the line segment.

  color:
    Line color.

  thickness:
    Line thickness. [By default this is 1]

  lineType:
    Type of the line. [By default this is LineType.Link8]

  shift:
     Number of fractional bits in the point coordinates. [By default this is 0]

1.1实例1-绘制线段拼成一个"王"字

代码如下：

Mat canvas = Mat.Zeros(300, 300, MatType.CV_8UC3);

Cv2.Line(canvas, new Point(50, 50), new Point(250, 50), new Scalar(255, 0, 0), 5);
Cv2.Line(canvas, new Point(50, 150), new Point(250, 150), new Scalar(0, 255, 0), 10);
Cv2.Line(canvas, new Point(50, 250), new Point(250, 250), new Scalar(0, 0, 255), 15);
Cv2.Line(canvas, new Point(150, 50), new Point(150, 250), new Scalar(0, 255, 255), 20);

Cv2.ImShow("lines", canvas);
Cv2.WaitKey();
Cv2.DestroyAllWindows();

效果

每条线段的起点坐标和终点坐标

2、矩形的绘制

OpenCvSharp提供Cv2.Rectangle方法，该方法既可以绘制矩形边框，也可以绘制实心矩形，其函数如下：

public static void Rectangle(InputOutputArray img, Point pt1, Point pt2, Scalar color, int thickness = 1, LineTypes lineType = LineTypes.Link8, int shift = 0)

说明：
摘要:
    Draws simple, thick or filled rectangle

参数:
  img:
    Image.

  pt1:
    One of the rectangle vertices.

  pt2:
    Opposite rectangle vertex.

  color:
    Line color (RGB) or brightness (grayscale image).

  thickness:
    Thickness of lines that make up the rectangle. Negative values make the function
    to draw a filled rectangle. [By default this is 1]

  lineType:
    Type of the line, see cvLine description. [By default this is LineType.Link8]

  shift:
    Number of fractional bits in the point coordinates. [By default this is 0]

2.1实例2-绘制一个矩形边框

代码如下：

Mat canvas = Mat.Zeros(300, 300, MatType.CV_8UC3);

Cv2.Rectangle(canvas, new Point(50, 50), new Point(200, 150), new Scalar(255, 0, 0), 20);

Cv2.ImShow("Rectangle", canvas);
Cv2.WaitKey();
Cv2.DestroyAllWindows();

效果

2.2实例3-绘制一个实心矩形

代码如下：

Mat canvas = Mat.Zeros(300, 300, MatType.CV_8UC3);

Cv2.Rectangle(canvas, new Point(50, 50), new Point(200, 150), new Scalar(255, 0, 0), -1);

Cv2.ImShow("Rectangle", canvas);
Cv2.WaitKey();
Cv2.DestroyAllWindows();

效果

3、圆的绘制

 OpenCvSharp提供Cv2.Circle方法，该方法既可以绘制圆形边框，也可以绘制实心圆形，Cv2.Circle函数如下：

public static void Circle(InputOutputArray img, int centerX, int centerY, int radius, Scalar color, int thickness = 1, LineTypes lineType = LineTypes.Link8, int shift = 0)

说明：

摘要:
     Draws a circle

 参数:
   img:
     Image where the circle is drawn.

   centerX:
     X-coordinate of the center of the circle.

   centerY:
     Y-coordinate of the center of the circle.

   radius:
     Radius of the circle.

   color:
     Circle color.

   thickness:
     Thickness of the circle outline if positive, otherwise indicates that a filled
     circle has to be drawn. [By default this is 1]

   lineType:
     Type of the circle boundary. [By default this is LineType.Link8]

   shift:
     Number of fractional bits in the center coordinates and radius value. [By default
     this is 0]

3.1实例4-绘制"交通灯"

代码如下：

Mat canvas = Mat.Zeros(300, 300, MatType.CV_8UC3);

Cv2.Circle(canvas, new Point(50, 150), 40, new Scalar(0, 0, 255), -1);

Cv2.Circle(canvas, new Point(150, 150), 40, new Scalar(0, 255, 255), -1);

Cv2.Circle(canvas, new Point(250, 150), 40, new Scalar(0, 255, 0), -1);

Cv2.ImShow("TrafficLights", canvas);
Cv2.WaitKey();
Cv2.DestroyAllWindows();

效果

4、多边形绘制

OpenCvSharp提供Polylines方法绘制多边形，其函数如下：

public static void Polylines(Mat img, IEnumerable<IEnumerable<Point>> pts, bool isClosed, Scalar color, int thickness = 1, LineTypes lineType = LineTypes.Link8, int shift = 0)

说明：

摘要:
    draws one or more polygonal curves

参数:
  img:
    画布
  pts:
    多边形各顶点组成的列表
  isClosed:
    是否闭合
  color:
    颜色
  thickness:
    线条宽度
  lineType:

  shift:

4.1实例5-绘制等腰梯形

代码如下：

Mat canvas = Mat.Zeros(300, 300, MatType.CV_8UC3);

List<OpenCvSharp.Point> pts1 = new List<OpenCvSharp.Point>
{
    new OpenCvSharp.Point(100,50),
    new OpenCvSharp.Point(200,50),
    new OpenCvSharp.Point(50,250),
    new OpenCvSharp.Point(250,250)
};

List<List<OpenCvSharp.Point>> pts = new List<List<Point>>();
pts.Add(pts1);

Cv2.Polylines(canvas, pts, true, new Scalar(0, 0, 255), 1);

Cv2.ImShow("Polylines", canvas);
Cv2.WaitKey();
Cv2.DestroyAllWindows();

效果

5、文字的绘制

OpenCvSharp提供Cv2.PutText方法进行文字绘制，其函数如下：

public static void PutText(InputOutputArray img, string text, Point org, HersheyFonts fontFace, double fontScale, Scalar color, int thickness = 1, LineTypes lineType = LineTypes.Link8, bool bottomLeftOrigin = false)

说明：

摘要:
    renders text string in the image

参数:
  img:
    Image.

  text:
    Text string to be drawn.

  org:
    Bottom-left corner of the text string in the image.

  fontFace:
    Font type, see #HersheyFonts.

  fontScale:
    Font scale factor that is multiplied by the font-specific base size.

  color:
    Text color.

  thickness:
    Thickness of the lines used to draw a text.

  lineType:
    Line type. See #LineTypes

  bottomLeftOrigin:
    When true, the image data origin is at the bottom-left corner. Otherwise, it is at the top-left corner.

5.1实例6-绘制文字OpenCvSharp

代码如下：

Mat canvas = Mat.Zeros(300, 300, MatType.CV_8UC3);

Cv2.PutText(canvas, "OpenCvSharp", new Point(0, 50), HersheyFonts.Italic, 1, new Scalar(0,255,0), 1, LineTypes.AntiAlias, false);

Cv2.ImShow("Text", canvas);
Cv2.WaitKey();
Cv2.DestroyAllWindows();

效果