如何实现Opencv画笔功能的方法

#include<iostream>
#include<opencv2/opencv.hpp>
 
using namespace std;
using namespace cv;
 
Rect g_rectangle;
bool g_bDrawing = false;
RNG g_rng(12345);
Point g_nCurrPoint;
int g_nThick = 0, g_nBlue = 255, g_nGreen = 255, g_nRed = 0;
 
/*注意：不能在毁掉函数中写入未初始化的矩阵类，所以需要用时，需要写一个标志位，然后再在while(1)循环内使用*/
void onMouse(int event, int x, int y, int flag, void *param)
{
 Mat &img = *(cv::Mat*)param;
 
 switch (event)
 {
 //移动鼠标的时候
 case CV_EVENT_MOUSEMOVE:
 {
   g_nCurrPoint = Point(x, y);
 }
 break;
 //点击鼠标左键时
 case CV_EVENT_LBUTTONDOWN:
 {
   g_bDrawing = true;
   g_nCurrPoint = Point(x, y);
 }
 break;
 //松开鼠标左键时
 case CV_EVENT_LBUTTONUP:
 {
   g_bDrawing = false;
 }
 break;
 }
}
 
int main()
{
 Mat srcImage(600, 800, CV_8UC3);
 Mat tempImage;
 
 srcImage.copyTo(tempImage);
 srcImage = Scalar::all(0);
 
 namedWindow("【鼠标事件窗口】", 0);
 setMouseCallback("【鼠标事件窗口】", onMouse, (void *)&srcImage);
 
 namedWindow("【滚动条窗口】", 0);
 createTrackbar("thick", "【滚动条窗口】", &g_nThick, 100, 0);
 createTrackbar("Blue", "【滚动条窗口】", &g_nBlue, 255, 0);
 createTrackbar("Green", "【滚动条窗口】", &g_nGreen, 255, 0);
 createTrackbar("Red", "【滚动条窗口】", &g_nRed, 255, 0);
 
 char key;
 while (1)
 {
 if (g_bDrawing)
 {
 circle(srcImage, g_nCurrPoint, 0, Scalar(g_nBlue, g_nGreen, g_nRed), g_nThick + 1);
 }
 
 imshow("【鼠标事件窗口】", srcImage);
 
 key = waitKey(1);
 if (key == 27)
 break;
 
 if (key == '1')
 srcImage = Scalar::all(0);
 
 /*DrawRectangle(srcImage, g_rectangle);
 imshow(WINDOW_NAME, srcImage);
 if (waitKey(10) == 27)
 break;*/
 }
 
 return 0;
}