基本的图形绘制

目标：
在该教程中你将学会如何去：
使用Point在图像中定义一个二维点；
使用Scalar以及为什么它有用；
使用OpenCV函数line绘制一条直线；
使用ellipse函数绘制一个椭圆
使用rectangle函数绘制矩形；
使用circle函数绘制圆形；
使用fillPoly绘制一个填充的多边形；
OpenCV理论：
在这个教程中，我们将着重使用两个结构：Point和Scalar。
Point:
它表示一个二维点，用图像的x和y坐标来表示。定义如下：
Pointpt;
pt.x = 10;
pt.y = 8;
或者：
Point pt=Point(10,8);
Scalar：
表示一个有4个元素的vector容器。Scalar在OpenCV中通常用来传递像素值。
在这个教程中，我们将把它扩展到去表示BGR颜色值（3个参数），最后一个参数如果没有用它就没必要去定义它。
让我们来看一个例子，如果我们要求一个颜色参数，那么我们给出下面的代码：
Scalar（a,b,c）
我们可以定义一个BGR颜色，例如：Blue=a,Green=b,Red=c
代码：

#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>

#define w 400

using namespace cv;

/// Function headers
void MyEllipse( Mat img, double angle );
void MyFilledCircle( Mat img, Point center );
void MyPolygon( Mat img );
void MyLine( Mat img, Point start, Point end );

/**
* @function main
* @brief Main function
*/
int main( void ){

/// Windows names
char atom_window[] = "Drawing 1: Atom";
char rook_window[] = "Drawing 2: Rook";

/// Create black empty images
Mat atom_image = Mat::zeros( w, w, CV_8UC3 );
Mat rook_image = Mat::zeros( w, w, CV_8UC3 );

/// 1. Draw a simple atom:
/// -----------------------

/// 1.a. Creating ellipses
MyEllipse( atom_image, 90 );
MyEllipse( atom_image, 0 );
MyEllipse( atom_image, 45 );
MyEllipse( atom_image, -45 );

/// 1.b. Creating circles
MyFilledCircle( atom_image, Point( w/2, w/2) );

/// 2. Draw a rook
/// ------------------

/// 2.a. Create a convex polygon
MyPolygon( rook_image );

/// 2.b. Creating rectangles
rectangle( rook_image,
Point( 0, 7*w/8 ),
Point( w, w),
Scalar( 0, 255, 255 ),
-1,
8 );

/// 2.c. Create a few lines
MyLine( rook_image, Point( 0, 15*w/16 ), Point( w, 15*w/16 ) );
MyLine( rook_image, Point( w/4, 7*w/8 ), Point( w/4, w ) );
MyLine( rook_image, Point( w/2, 7*w/8 ), Point( w/2, w ) );
MyLine( rook_image, Point( 3*w/4, 7*w/8 ), Point( 3*w/4, w ) );

/// 3. Display your stuff!
imshow( atom_window, atom_image );
moveWindow( atom_window, 0, 200 );
imshow( rook_window, rook_image );
moveWindow( rook_window, w, 200 );

waitKey( 0 );
return(0);
}

/// Function Declaration

/**
* @function MyEllipse
* @brief Draw a fixed-size ellipse with different angles
*/
void MyEllipse( Mat img, double angle )
{
int thickness = 2;
int lineType = 8;

ellipse( img,
Point( w/2, w/2 ),
Size( w/4, w/16 ),
angle,
0,
360,
Scalar( 255, 0, 0 ),
thickness,
lineType );
}

/**
* @function MyFilledCircle
* @brief Draw a fixed-size filled circle
*/
void MyFilledCircle( Mat img, Point center )
{
int thickness = -1;
int lineType = 8;

circle( img,
center,
w/32,
Scalar( 0, 0, 255 ),
thickness,
lineType );
}

/**
* @function MyPolygon
* @function Draw a simple concave polygon (rook)
*/
void MyPolygon( Mat img )
{
int lineType = 8;

/** Create some points */
Point rook_points[1][20];
rook_points[0][0]  = Point(    w/4,   7*w/8 );
rook_points[0][1]  = Point(  3*w/4,   7*w/8 );
rook_points[0][2]  = Point(  3*w/4,  13*w/16 );
rook_points[0][3]  = Point( 11*w/16, 13*w/16 );
rook_points[0][4]  = Point( 19*w/32,  3*w/8 );
rook_points[0][5]  = Point(  3*w/4,   3*w/8 );
rook_points[0][6]  = Point(  3*w/4,     w/8 );
rook_points[0][7]  = Point( 26*w/40,    w/8 );
rook_points[0][8]  = Point( 26*w/40,    w/4 );
rook_points[0][9]  = Point( 22*w/40,    w/4 );
rook_points[0][10] = Point( 22*w/40,    w/8 );
rook_points[0][11] = Point( 18*w/40,    w/8 );
rook_points[0][12] = Point( 18*w/40,    w/4 );
rook_points[0][13] = Point( 14*w/40,    w/4 );
rook_points[0][14] = Point( 14*w/40,    w/8 );
rook_points[0][15] = Point(    w/4,     w/8 );
rook_points[0][16] = Point(    w/4,   3*w/8 );
rook_points[0][17] = Point( 13*w/32,  3*w/8 );
rook_points[0][18] = Point(  5*w/16, 13*w/16 );
rook_points[0][19] = Point(    w/4,  13*w/16 );

const Point* ppt[1] = { rook_points[0] };
int npt[] = { 20 };

fillPoly( img,
ppt,
npt,
1,
Scalar( 255, 255, 255 ),
lineType );
}

/**
* @function MyLine
* @brief Draw a simple line
*/
void MyLine( Mat img, Point start, Point end )
{
int thickness = 2;
int lineType = 8;
line( img,
start,
end,
Scalar( 0, 0, 0 ),
thickness,
lineType );
}

解释：
1、因为我们打算去绘制两幅图像(一个atom和一个rook)，我们需要去创建2个图像以及两个窗口去显示他们。

/// Windows names
char atom_window[] = "Drawing 1: Atom";
char rook_window[] = "Drawing 2: Rook";

/// Create black empty images
Mat atom_image = Mat::zeros( w, w, CV_8UC3 );
Mat rook_image = Mat::zeros( w, w, CV_8UC3 );

2、然后我们创建函数去绘制不同的几何形状；

MyEllipse( atom_image, 90 );
MyEllipse( atom_image, 0 );
MyEllipse( atom_image, 45 );
MyEllipse( atom_image, -45 );
MyFilledCircle( atom_image, Point( w/2.0, w/2.0) );

3、绘制rook的时候我们调用MyLine,rectangle和MyPolygon

MyPolygon( rook_image );

/// 2.b. Creating rectangles
rectangle( rook_image,
Point( 0, 7*w/8.0 ),<pre name="code" class="cpp">void MyLine( Mat img, Point start, Point end )
{
int thickness = 2;
int lineType = 8;
line( img,
start,
end,
Scalar( 0, 0, 0 ),
thickness,
lineType );
}

Point( w, w), Scalar( 0, 255, 255 ), -1, 8 );/// 2.c. Create a few linesMyLine( rook_image, Point( 0, 15*w/16 ), Point( w, 15*w/16 ) );MyLine( rook_image, Point( w/4, 7*w/8 ), Point( w/4, w ) );MyLine( rook_image, Point( w/2, 7*w/8 ), Point( w/2, w ) );MyLine(
rook_image, Point( 3*w/4, 7*w/8 ), Point( 3*w/4, w ) );

4、让我们来看看这些函数里面是什么：

void MyLine( Mat img, Point start, Point end )
{
int thickness = 2;
int lineType = 8;
line( img,
start,
end,
Scalar( 0, 0, 0 ),
thickness,
lineType );
}

正如我们所看到的，MyLine函数仅仅调用了函数line:
从起点start到终点end之间绘制一条直线；
这条线在图像img中显示；
线的颜色被Scalar定义为黑色；
线宽被设置为2；
线的类型属于8连通的。

void MyEllipse( Mat img, double angle )
{
int thickness = 2;
int lineType = 8;

ellipse( img,
Point( w/2.0, w/2.0 ),
Size( w/4.0, w/16.0 ),
angle,
0,
360,
Scalar( 255, 0, 0 ),
thickness,
lineType );
}

椭圆在img中显示；
椭圆中心在点（w/2,w/2）并且被一个大小为(w/4,w/16)的矩形所包络；
这个椭圆旋转了angle角度；
这个椭圆外延了0-360°之间的弧度；
图像的颜色被定义为Scalar(255,0,0)，在BGR中表示Blue蓝色；
这个椭圆的线宽为2；

void MyFilledCircle( Mat img, Point center )
{
int thickness = -1;
int lineType = 8;

circle( img,
center,
w/32.0,
Scalar( 0, 0, 255 ),
thickness,
lineType );
}

图像在Img中显示；
圆形的圆心在center；
圆的半径是w/32；
圆的颜色定义为Scalar(0，0，225),在BGR中表示红色；

Thickness=-1，表示圆形将被填充。

void MyPolygon( Mat img )
{
int lineType = 8;

/** Create some points */
Point rook_points[1][20];
rook_points[0][0] = Point( w/4.0, 7*w/8.0 );
rook_points[0][1] = Point( 3*w/4.0, 7*w/8.0 );
rook_points[0][2] = Point( 3*w/4.0, 13*w/16.0 );
rook_points[0][3] = Point( 11*w/16.0, 13*w/16.0 );
rook_points[0][4] = Point( 19*w/32.0, 3*w/8.0 );
rook_points[0][5] = Point( 3*w/4.0, 3*w/8.0 );
rook_points[0][6] = Point( 3*w/4.0, w/8.0 );
rook_points[0][7] = Point( 26*w/40.0, w/8.0 );
rook_points[0][8] = Point( 26*w/40.0, w/4.0 );
rook_points[0][9] = Point( 22*w/40.0, w/4.0 );
rook_points[0][10] = Point( 22*w/40.0, w/8.0 );
rook_points[0][11] = Point( 18*w/40.0, w/8.0 );
rook_points[0][12] = Point( 18*w/40.0, w/4.0 );
rook_points[0][13] = Point( 14*w/40.0, w/4.0 );
rook_points[0][14] = Point( 14*w/40.0, w/8.0 );
rook_points[0][15] = Point( w/4.0, w/8.0 );
rook_points[0][16] = Point( w/4.0, 3*w/8.0 );
rook_points[0][17] = Point( 13*w/32.0, 3*w/8.0 );
rook_points[0][18] = Point( 5*w/16.0, 13*w/16.0 );
rook_points[0][19] = Point( w/4.0, 13*w/16.0) ;

const Point* ppt[1] = { rook_points[0] };
int npt[] = { 20 };

fillPoly( img,
ppt,
npt,
1,
Scalar( 255, 255, 255 ),
lineType );
}

多边形在img中显示；
多边形的定点被设置为ppt中的点；
顶点的总数在npt中；
多边形的数量是1，即只绘制一个多边形；
颜色被设置为白色。

rectangle( rook_image,
Point( 0, 7*w/8.0 ),
Point( w, w),
Scalar( 0, 255, 255 ),
-1,
8 );

图像在rook_image中显示；
对角线上的顶点坐标被Point(0,7*w/8)和Point(w,w)定义；
颜色设置为黄色；
Thickness=-1，表示图像将被填充
效果：