本节你将学到:
本节中,我门将大量使用 Point 和 Scalar 这两个结构:
表示了具有4个元素的数组。次类型在OpenCV中被大量用于传递像素值。
本节中,我们将进一步用它来表示RGB颜色值(三个参数)。如果用不到第四个参数,则无需定义。
我们来看个例子,如果给出以下颜色参数表达式:
Scalar( a, b, c )
那么定义的RGB颜色值为: Red = c, Green = b and Blue = a
我们打算画两个例子(原子和赌棍), 所以必须创建两个图像和对应的窗口以显示。
/// 窗口名字
char atom_window[] = "Drawing 1: Atom";
char rook_window[] = "Drawing 2: Rook";
/// 创建空全黑像素的空图像
Mat atom_image = Mat::zeros( w, w, CV_8UC3 );
Mat rook_image = Mat::zeros( w, w, CV_8UC3 );
创建用来画不同几何形状的函数。比如用 MyEllipse 和 MyFilledCircle 来画原子。
/// 1. 画一个简单的原子。
/// 1.a. 创建椭圆
MyEllipse( atom_image, 90 );
MyEllipse( atom_image, 0 );
MyEllipse( atom_image, 45 );
MyEllipse( atom_image, -45 );
/// 1.b. 创建圆
MyFilledCircle( atom_image, Point( w/2.0, w/2.0) );
接下来用 MyLine*,*rectangle 和 a MyPolygon 来画赌棍:
/// 2. 画一个赌棍
/// 2.a. 创建一个凸多边形
MyPolygon( rook_image );
/// 2.b. 创建矩形
rectangle( rook_image,
Point( 0, 7*w/8.0 ),
Point( w, w),
Scalar( 0, 255, 255 ),
-1,
8 );
/// 2.c. 画几条直线
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 ) );
现在来看看每个函数内部如何定义:
MyLine
void MyLine( Mat img, Point start, Point end )
{
int thickness = 2;
int lineType = 8;
line( img,
start,
end,
Scalar( 0, 0, 0 ),
thickness,
lineType );
}
正如我们所见, MyLine 调用函数 line 来实现以下操作:
MyEllipse
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 );
}
根据以上代码,我们可看到函数 ellipse 按照以下规则绘制椭圆:
MyFilledCircle
void MyFilledCircle( Mat img, Point center )
{
int thickness = -1;
int lineType = 8;
circle( img,
center,
w/32.0,
Scalar( 0, 0, 255 ),
thickness,
lineType );
}
类似于椭圆函数,我们可以看到 circle 函数的参数意义如下:
MyPolygon
void MyPolygon( Mat img )
{
int lineType = 8;
/** 创建一些点 */
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 );
}
我们用函数 :fill_poly:`fillPoly <>` 来绘制填充的多边形。请注意:
rectangle
rectangle( rook_image,
Point( 0, 7*w/8.0 ),
Point( w, w),
Scalar( 0, 255, 255 ),
-1,
8 );
最后是函数:rectangle:rectangle <> (我们并没有为这家伙创建特定函数)。请注意:
编译并运行例程,你将看到如下结果:
刘瑞华 <lurvhua@163.com>