Using mouse to draw lines on video with OpenCV - visual-studio-2010

Question

I have been playing with OpenCV (I am pretty new to it) to display live camera. What I wanted to do next was to draw lines on it with my mouse. Does anyone know how to do this? So far, what I have is:
#include "stdafx.h"
#include <stdio.h>
#include "cv.h"
#include "highgui.h"
int main( int argc, char **argv )
{
CvCapture *capture = 0;
IplImage *frame = 0;
int key = 0;
/* initialize camera */
capture = cvCaptureFromCAM( 0 );
/* always check */
if ( !capture ) {
fprintf( stderr, "Cannot open initialize webcam!\n" );
return 1;
}
/* create a window for the video */
cvNamedWindow( "Testing", CV_WINDOW_AUTOSIZE );
while( key != 'q' ) {
/* get a frame */
frame = cvQueryFrame( capture );
/* always check */
if( !frame ) break;
/* display current frame */
cvShowImage( "result", frame );
/* exit if user press 'q' */
key = cvWaitKey( 1 );
}
/* free memory */
cvDestroyWindow( "result" );
cvReleaseCapture( &capture );
return 0;
}
If anyone could help me draw lines on the live video, or if anyone knows of any tips, I'd greatly appreciate it! Thanks!

Answer 1

If it helps, here is my code for drawing rectangles on multiple sized video streams
#include "stdafx.h"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#define SSTR( x ) dynamic_cast< std::ostringstream & >(( std::ostringstream() << std::dec << x ) ).str()
using namespace std;
using namespace cv;
Rect box; //global structures needed for drawing
bool drawing_box = false;
struct mousecallbackstruct{
Mat* src;
Mat* overlay;
string windowname;
};
Mat srcoverlay,smallsrcoverlay; //an overlay must be created for each window you want to draw on
void onMouse(int event, int x, int y, int flags, void* param) //it seems the only way to use this is by keeping different globals for different windows - meaning you have to set up all thise ahead of time, and keep track of it and not mix/match windows/frames!! horrible design here.
{
cout << event;
mousecallbackstruct mousestruct;
mousestruct = *((mousecallbackstruct*)param);
Mat* srcp = mousestruct.src;
Mat* overlayp = mousestruct.overlay; // yeah, yeah, i use 7 lines where I could use 3, so sue me
Mat src = *srcp;
Mat overlay = *overlayp;
if(!src.data){
cout << "your void * cast didn't work :(\n";
return;
}
switch( event ){
case CV_EVENT_MOUSEMOVE:
if( drawing_box ){
box.width = x-box.x;
box.height = y-box.y;
}
break;
case CV_EVENT_LBUTTONDOWN: //start drawing
drawing_box = true;
box = cvRect( x, y, 0, 0 );
break;
case CV_EVENT_LBUTTONDBLCLK: //double click to clear
drawing_box = false;
overlay.setTo(cv::Scalar::all(0)); //clear it
break;
case CV_EVENT_LBUTTONUP: //draw what we created with Lbuttondown
drawing_box = false;
if( box.width < 0 ){
box.x += box.width;
box.width *= -1;
}
if( box.height < 0 ){
box.y += box.height;
box.height *= -1;
}
rectangle( overlay, Point(box.x, box.y), Point(box.x+box.width,box.y+box.height),CV_RGB(100,200,100),4); //draw rectangle. You can change this to line or circle or whatever. Maybe with the Right mouse button.
break;
}
}
void iimshow(mousecallbackstruct* mystructp){ //this is where we add the text/drawing created in the mouse handler to the actual image (since mouse handler events do not coincide with the drawing events)
mousecallbackstruct mystruct = *mystructp; //custom struct made for the mouse callback - very handy for other functions too
Mat overlay, src;
Mat* srcp = mystruct.src;
Mat* overlayp = mystruct.overlay;
src = *srcp; // yeah, yeah, i use 9 lines where I could use 3, so sue me
overlay = *overlayp;
string name = mystruct.windowname;
Mat added,imageROI;
try{
//cout << "tch:" << overlay.rows << "," << src.rows << ";" << overlay.cols << "," << src.cols << ";" << src.channels() << "," << overlay.channels() <<"," << src.type() << "," << overlay.type() << "\n";
if(overlay.data && overlay.rows == src.rows && overlay.cols == src.cols && overlay.channels() == src.channels()){ //basic error checking
add(src,overlay,added);
}else{
//try to resize it
imageROI= overlay(Rect(0,0,src.cols,src.rows));
add(src,imageROI,added);
}
imshow(name,added);// the actual draw moment
}catch(...){ //if resize didn't work then this should catch it and you can see what didn't match up
cout << "Error. Mismatch:" << overlay.rows << "," << src.rows << ";" << overlay.cols << "," << src.cols << ";" << src.channels() << "," << overlay.channels() <<"," << src.type() << "," << overlay.type() << "\n";
imshow(name + "overlay",overlay);
imshow(name+"source",src);
}
}
int _tmain(int argc, _TCHAR* argv[]){
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) { // check if we succeeded
cout << "NO camera found \n";
return -1;
}
Mat src,smallsrc,overlay;
cap >> src; //grab 1 frame to build our preliminary Mats and overlays
srcoverlay.create(src.rows,src.cols,src.type()); //create overlays
smallsrcoverlay.create(src.rows,src.cols,src.type());
srcoverlay.setTo(cv::Scalar::all(0)); //clear it
smallsrcoverlay.setTo(cv::Scalar::all(0)); //clear it
namedWindow( "smallsrc", CV_WINDOW_AUTOSIZE );
namedWindow( "source", CV_WINDOW_AUTOSIZE ); //these must be created early for the setmousecallback, AND you have to know what Mats will be using them and not switch them around :(
moveWindow("smallsrc",1000,100); //create a small original capture off to the side of screen
////////////// for each window/mat that uses a mouse handler, you must create one of these structures for it and pass it into the mouse handler, and add a global mat for overlays (at top of code)
mousecallbackstruct srcmousestruct,smallsrcmousestruct; //these get passed into the mouse callback function. Hopefully they update their contents automatically for the callback? :(
srcmousestruct.overlay = &srcoverlay; //fill our custom struct
srcmousestruct.src = &src;
srcmousestruct.windowname = "source";
smallsrcmousestruct.overlay = &smallsrcoverlay; //the small window
smallsrcmousestruct.src = &smallsrc;
smallsrcmousestruct.windowname = "smallsrc";
setMouseCallback(smallsrcmousestruct.windowname, onMouse, (void*)&smallsrcmousestruct); //the actual 'set mouse callback' call
setMouseCallback(srcmousestruct.windowname, onMouse, (void*)&srcmousestruct);
for(;;){ //main loop
/// Load an image
cap >> src;
if( !src.data )
{ return -1; }
resize(src,smallsrc,Size(),.5,.5); //smaller scale window of original
overlay = *srcmousestruct.overlay;
src = *srcmousestruct.src;
iimshow(&srcmousestruct); //my imshow replacement. uses structs
iimshow(&smallsrcmousestruct);
if(waitKey(30) == 27) cin.get(); //esc pauses
}
cin.get();
return 0;
}

Answer 2

You will have to be more clear as to what you mean by drawing on the video.
One option is to handle the mouse positions, by drawing the lines between them, on a black/blank "mask" image, and "apply" this image to each video frame before it is displayed.

Answer 3

To capture mouse events you need to create a callback. This callback will be tied to a specific named window. The documentation for the call cvSetMouseCallback is pretty good. The callback function will know current position and button click information. From there you can capture points on mouse clicks and use those points with cvLine to draw on your frame.