---

前言

本案例将使用OpenCV C++实现动态时钟效果。原理也很简单，主要分为绘制表盘、以及获取系统时间两步。

一、绘制表盘

首先为了效果显示美观一点，选取一张背景图。

接着需要绘制一个圆形表盘，直接上代码、效果演示。注释都在源码上有标注。

	Point center(background.cols / 2, background.rows / 2);//圆心int radius = min(background.cols / 2, background.rows / 2) - 20; //时钟半径Mat mask = Mat::zeros(background.size(), CV_8UC3);circle(mask, center, radius, Scalar::all(255), -1);//掩模Mat canvas = Mat(background.size(), CV_8UC3, Scalar(175, 165, 0));//创建画布background.copyTo(canvas, mask);//将背景拷贝到画布中，形成表盘背景circle(canvas, center, radius, Scalar::all(0), 3);//表盘

二、绘制刻线

接下来，需要在表盘上绘制时针、分针刻线。其中原理就是计算点的旋转坐标。可以参考一下我的这篇博文OpenCV C++案例实战二十七《角度测量》

	int margin = 5;//若margin为0，则点在表盘上//画分针刻线int minute_len = 10; //刻线长度for (int i = 0; i < 60; i++){//圆上坐标点计算公式，对于分针刻线，360/60=6，即每隔6°一刻线int x1 = center.x + (radius - margin) * cos(i*6.0*CV_PI / 180.0);int y1 = center.y + (radius - margin) * sin(i*6.0*CV_PI / 180.0);int x2 = center.x + (radius - minute_len) * cos(i*6.0*CV_PI / 180.0);int y2 = center.y + (radius - minute_len) * sin(i*6.0*CV_PI / 180.0);line(canvas, Point(x1, y1), Point(x2, y2), Scalar::all(0), 2, LINE_AA);}//画时针刻线int hour_len = 20;for (int i = 0; i < 12; i++){//对于时针刻线，每隔360/12=30，即每隔30°一刻线int x1 = center.x + (radius - margin) * cos(i*30.0*CV_PI / 180.0);int y1 = center.y + (radius - margin) * sin(i*30.0*CV_PI / 180.0);int x2 = center.x + (radius - hour_len)*cos(i*30.0*CV_PI / 180.0);int y2 = center.y + (radius - hour_len)*sin(i*30.0*CV_PI / 180.0);line(canvas, Point(x1, y1), Point(x2, y2), Scalar::all(0), 3, LINE_AA);//在表盘上显示3、6、9、12时，坐标位置自行根据图像大小设定if (i == 0){putText(canvas, to_string(i + 3), Point(x2 - 30, y2 + 10), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}else if (i == 3){putText(canvas, to_string(i + 3), Point(x2 - 10, y2 - 10), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}else if (i == 6){putText(canvas, to_string(i + 3), Point(x2 + 10, y2 + 10), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}else if (i == 9){putText(canvas, to_string(i + 3), Point(x2 - 20, y2 + 30), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}}

效果如上图所示，至此前期的预处理工作已经完成了。接下来，需要获取系统时间，然后绘制到表盘上。

三、获取系统时间

当我们获取到相应的系统时间后，有一点需要注意的是，opencv是以3点钟方向为起点，即0°方向，且为顺时针旋转，故秒针、分针、时针在0~3点钟区间需要换算。具体换算请看源码注释。

	//使用while循环，不断更新时间while (true){	char key = waitKey(1000);if (key == 27)break;Mat clockImg = canvas.clone();//将表盘复制一份，用于不断更新时钟刻线//获取系统时间SYSTEMTIME Time;GetLocalTime(&Time);int second = Time.wSecond; //秒int minute = Time.wMinute; //分int hour = Time.wHour; //时int day = Time.wDay; //日int month = Time.wMonth; //月int year = Time.wYear; //年printf("%4d/%02d/%02d %02d:%02d:%02d\n", year, month, day, hour, minute, second);//由于opencv是以3点钟方向为起点，且为顺时针旋转，故秒针、分针、时针在0~3点钟区间需要换算//秒针int sec_angle = 0;if (second <= 15){//当秒针处于0~15秒时，对应角度应处于270~360°，每隔6°走一刻线sec_angle = second * 6 + 270;}else{sec_angle = (second - 15) * 6;}int sec_x = center.x + (radius - margin * 12) *cos(sec_angle*CV_PI / 180);int sec_y = center.y + (radius - margin * 12) *sin(sec_angle*CV_PI / 180);line(clockImg, center, Point(sec_x, sec_y), Scalar(0, 255, 0), 2, LINE_AA);//分针int min_angle = 0;if (minute <= 15){//当分针处于0~15分时，对应角度应处于270~360°，每隔6°走一刻线min_angle = minute * 6 + 270;}else{min_angle = (minute - 15) * 6;}int min_x = center.x + (radius - margin*18)*cos(min_angle*CV_PI / 180);int min_y = center.y + (radius - margin*18)*sin(min_angle*CV_PI / 180);line(clockImg, center, Point(min_x, min_y), Scalar(0, 255, 255), 4, LINE_AA);//时针int hour_angle = 0;if (hour <= 3){//当时针处于0~3时，对应角度应处于270~360°，每隔30°走一刻线hour_angle = hour * 30 + 270;}else{hour_angle = (hour - 3) * 30;}int hour_x = center.x + (radius - margin * 24)*cos(hour_angle*CV_PI / 180);int hour_y = center.y + (radius - margin * 24)*sin(hour_angle*CV_PI / 180);line(clockImg, center, Point(hour_x, hour_y), Scalar(255, 255, 0), 6, LINE_AA);circle(clockImg, center, 5, Scalar::all(0), -1);//将时间显示在表盘上char text1[100], text2[100];sprintf_s(text1, "%04d%s%02d%s%02d", year, "/", month, "/", day);sprintf_s(text2, "%02d%s%02d%s%02d", hour, ":", minute, ":", second);putText(clockImg, text1, Point(center.x-100, center.y+200), FONT_HERSHEY_SIMPLEX, 1, Scalar(21, 23, 161), 3);putText(clockImg, text2, Point(center.x-70, center.y+250), FONT_HERSHEY_SIMPLEX, 1, Scalar(21, 23, 161), 2);imshow("dynamic clock", clockImg);imwrite("dynamic clock.jpg", clockImg);}

四、结果展示

五、源码

#include<iostream>
#include<opencv2/opencv.hpp>
#include<Windows.h>
using namespace std;
using namespace cv;int main()
{Mat background = imread("background.jpg");if (background.empty()){cout << "can not read the image..." << endl;system("pause");return -1;}Point center(background.cols / 2, background.rows / 2);//圆心int radius = min(background.cols / 2, background.rows / 2) - 20; //时钟半径Mat mask = Mat::zeros(background.size(), CV_8UC3);circle(mask, center, radius, Scalar::all(255), -1);//掩模Mat canvas = Mat(background.size(), CV_8UC3, Scalar(175, 165, 0));//创建画布background.copyTo(canvas, mask);//将背景拷贝到画布中，形成表盘背景circle(canvas, center, radius, Scalar::all(0), 3);//表盘int margin = 5;//若margin为0，则点在表盘上//画分针刻线int minute_len = 10; //刻线长度for (int i = 0; i < 60; i++){//圆上坐标点计算公式，对于分针刻线，360/60=6，即每隔6°一刻线int x1 = center.x + (radius - margin) * cos(i*6.0*CV_PI / 180.0);int y1 = center.y + (radius - margin) * sin(i*6.0*CV_PI / 180.0);int x2 = center.x + (radius - minute_len) * cos(i*6.0*CV_PI / 180.0);int y2 = center.y + (radius - minute_len) * sin(i*6.0*CV_PI / 180.0);line(canvas, Point(x1, y1), Point(x2, y2), Scalar::all(0), 2, LINE_AA);}//画时针刻线int hour_len = 20;for (int i = 0; i < 12; i++){//对于时针刻线，每隔360/12=30，即每隔30°一刻线int x1 = center.x + (radius - margin) * cos(i*30.0*CV_PI / 180.0);int y1 = center.y + (radius - margin) * sin(i*30.0*CV_PI / 180.0);int x2 = center.x + (radius - hour_len)*cos(i*30.0*CV_PI / 180.0);int y2 = center.y + (radius - hour_len)*sin(i*30.0*CV_PI / 180.0);line(canvas, Point(x1, y1), Point(x2, y2), Scalar::all(0), 3, LINE_AA);//在表盘上显示3、6、9、12时，坐标位置自行根据图像大小设定if (i == 0){putText(canvas, to_string(i + 3), Point(x2 - 30, y2 + 10), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}else if (i == 3){putText(canvas, to_string(i + 3), Point(x2 - 10, y2 - 10), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}else if (i == 6){putText(canvas, to_string(i + 3), Point(x2 + 10, y2 + 10), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}else if (i == 9){putText(canvas, to_string(i + 3), Point(x2 - 20, y2 + 30), FONT_HERSHEY_SIMPLEX, 1, Scalar::all(0), 3);}}//使用while循环，不断更新时间while (true){	char key = waitKey(1000);if (key == 27)break;Mat clockImg = canvas.clone();//将表盘复制一份，用于不断更新时钟刻线//获取系统时间SYSTEMTIME Time;GetLocalTime(&Time);int second = Time.wSecond; //秒int minute = Time.wMinute; //分int hour = Time.wHour; //时int day = Time.wDay; //日int month = Time.wMonth; //月int year = Time.wYear; //年printf("%4d/%02d/%02d %02d:%02d:%02d\n", year, month, day, hour, minute, second);//由于opencv是以3点钟方向为起点，且为顺时针旋转，故秒针、分针、时针在0~3点钟区间需要换算//秒针int sec_angle = 0;if (second <= 15){//当秒针处于0~15秒时，对应角度应处于270~360°，每隔6°走一刻线sec_angle = second * 6 + 270;}else{sec_angle = (second - 15) * 6;}int sec_x = center.x + (radius - margin * 12) *cos(sec_angle*CV_PI / 180);int sec_y = center.y + (radius - margin * 12) *sin(sec_angle*CV_PI / 180);line(clockImg, center, Point(sec_x, sec_y), Scalar(0, 255, 0), 2, LINE_AA);//分针int min_angle = 0;if (minute <= 15){//当分针处于0~15分时，对应角度应处于270~360°，每隔6°走一刻线min_angle = minute * 6 + 270;}else{min_angle = (minute - 15) * 6;}int min_x = center.x + (radius - margin*18)*cos(min_angle*CV_PI / 180);int min_y = center.y + (radius - margin*18)*sin(min_angle*CV_PI / 180);line(clockImg, center, Point(min_x, min_y), Scalar(0, 255, 255), 4, LINE_AA);//时针int hour_angle = 0;if (hour <= 3){//当时针处于0~3时，对应角度应处于270~360°，每隔30°走一刻线hour_angle = hour * 30 + 270;}else{hour_angle = (hour - 3) * 30;}int hour_x = center.x + (radius - margin * 24)*cos(hour_angle*CV_PI / 180);int hour_y = center.y + (radius - margin * 24)*sin(hour_angle*CV_PI / 180);line(clockImg, center, Point(hour_x, hour_y), Scalar(255, 255, 0), 6, LINE_AA);circle(clockImg, center, 5, Scalar::all(0), -1);//将时间显示在表盘上char text1[100], text2[100];sprintf_s(text1, "%04d%s%02d%s%02d", year, "/", month, "/", day);sprintf_s(text2, "%02d%s%02d%s%02d", hour, ":", minute, ":", second);putText(clockImg, text1, Point(center.x-100, center.y+200), FONT_HERSHEY_SIMPLEX, 1, Scalar(21, 23, 161), 3);putText(clockImg, text2, Point(center.x-70, center.y+250), FONT_HERSHEY_SIMPLEX, 1, Scalar(21, 23, 161), 2);imshow("dynamic clock", clockImg);imwrite("dynamic clock.jpg", clockImg);}destroyAllWindows();system("pause");return 0;
}

---

总结

本文使用OpenCV C++ 进行动态时钟绘制，主要操作有以下几点。
1、图像预处理，绘制表盘
2、绘制表盘刻线
3、获取系统时间，注意角度与时间之间的转换