Failed to draw multiple lines on an image using mouse click - c++

Question

I have learnt how to draw a line on an image in OpenCV using line( frame, Point( 15, 20 ), Point( 70, 50), 'r', 2, 8 );
I have also learnt how to draw a line on image using mouse clicks. For example the following code draws a line connecting two points user clicks on an image:
using namespace cv;
using namespace std;
void onMouse(int evt, int x, int y, int flags, void* param) {
if(evt == CV_EVENT_LBUTTONDOWN) {
std::vector<cv::Point>* ptPtr = (std::vector<cv::Point>*)param;
ptPtr->push_back(cv::Point(x,y));
}
}
int main()
{
std::vector<Point> points;
cv::namedWindow("Output Window");
Mat frame = cv::imread("chhha.png");
cv::setMouseCallback("Output Window", onMouse, (void*)&points);
int X1=0, Y1=0, X2=0, Y2=0;
while(1)
{
cv::imshow("Output Window", frame);
if (points.size() > 1) //we have 2 points
{
for (auto it = points.begin(); it != points.end(); ++it)
{
}
break;
}
waitKey(10);
}
// Now let us draw a line on the image
line( frame, points[0], points[1], 'r', 2, 8 );
cv::imshow("Output Window", frame);
waitKey( 10 );
getch();
return 0;
}
Now basically what I want is to keep drawing the lines until I right click or may be some character is entered.
What I have tried so far is using do-while loop:
char m;
do{
while(1)
{
cv::imshow("Output Window", frame);
if (points.size() > 1) //we have 2 points
{
for (auto it = points.begin(); it != points.end(); ++it)
{
}
break;
}
waitKey(10);
}
// Draw a line
line( frame, points[0], points[1], 'r', 2, 8 );
cv::imshow("Output Window", frame);
cout<<"do you want more lines, if so , press 'y'"<<endl;
cin>>m;
// instead of this a right click check would be much better
if(m!='y')
{
break;
}
}while(m=='y');
But the problem is this way not even one line would be drawn, and after few clicks and entering 'y', the application won't respond.
Please help me solve this issue.

Answer 1

There are probably several issues with your code that prevent it from doing what you want. The first thing that comes to mind is that you're not clearing the vector used for capturing the coordinates. After drawing a line
line( frame, points[0], points[1], 'r', 2, 8 );
you should reset the vector like this
points.clear();
so that the next mouse click's coordinate goes to points[0]. Otherwise it would append to the vector and you would keep drawing lines between the first two mouse coordinates over and over again.