How to use setMouseCallback to draw random line? - c++

Question

I've studied Opencv's setMouseCallback function.
I understand there are several events, list below:
CV_EVENT_MOUSEMOVE 0,
CV_EVENT_LBUTTONDOWN 1,
CV_EVENT_RBUTTONDOWN 2,
CV_EVENT_MBUTTONDOWN 3,
CV_EVENT_LBUTTONUP 4,
CV_EVENT_RBUTTONUP 5,
CV_EVENT_MBUTTONUP 6,
CV_EVENT_LBUTTONDBLCLK 7,
CV_EVENT_RBUTTONDBLCLK 8,
CV_EVENT_MBUTTONDBLCLK 9,
CV_EVENT_FLAG_LBUTTON 1,
CV_EVENT_FLAG_RBUTTON 2,
CV_EVENT_FLAG_MBUTTON 4,
CV_EVENT_FLAG_CTRLKEY 8,
CV_EVENT_FLAG_SHIFTKEY 16,
CV_EVENT_FLAG_ALTKEY 32,
and with the coordinates I get from these events, I can draw, for example: straight line, circle, ellipse...etc.
But instead of straight line, I want to draw random line, just like the "pencil" or "brush" function in Microsoft Paint.
The CV_EVENT_MOUSEMOVE does return all the coordinates as my mouse move through the image, but I don't know how to combine it with CV_EVENT_LBUTTONDOWN to represent "Start drawing line" and CV_EVENT_LBUTTONUP to represent "Finish drawing line"?
Does anyone know how to achieve my requirement with setMouseCallback?

Answer 1

I figured it out myself,
bool trigger;
Mat img;
void onMouse(int event, int x, int y, int flag, int param)
{
if(event == CV_EVENT_LBUTTONDOWN)
{
img = Mat::zeros(320, 240, CV_8UC3);
trigger = true;
}
if(event == CV_EVENT_LBUTTONUP)
{
trigger = false;
}
if(event == CV_EVENT_MOUSEMOVE)
{
if(trigger == true)
{
line(img, cvPoint(x, y), cvPoint(x, y), Scalar(0, 0, 255), 3, CV_AA, 0);
imshow("Drawing", img);
}
}
}
int main(int argc, char *argv[])
{
.
.
.
cvsetMouseCallback("Origin img", onMouse, NULL);
.
.
.
}