How to make cv::setMouseCallback function work - c++

Question

I've seen a few questions that are probably the same. I am still unable to make my code work after reading the answers. So I am sorry in advance if I am repeating the posts.
I managed to write this code :
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#include <string>
bool leftButtonDown = false, leftButtonUp = false;
cv::Mat img;
cv::Point cor1, cor2;
cv::Rect rect;
void mouseCall(int event, int x, int y, int, void*) {
if (event == cv::EVENT_LBUTTONDOWN) //finding first corner
{
leftButtonDown = true; cor1.x = x; cor1.y = y; std::cout << "Corner 1: " << cor1 << std::endl;
}
if (event == cv::EVENT_LBUTTONUP) {
if (abs(x - cor1.x)>20 && abs(y - cor1.y)>5) //finding second corner and checking whether the region is too small
{
leftButtonUp = true; cor2.x = x; cor2.y = y; std::cout << "Corner 2: " << cor2 << std::endl;
}
else { std::cout << "Select more than 5 pixels" << std::endl; }
}
if (leftButtonDown == true && leftButtonUp == false) //when the left button is clicked and let off
{ //draw a rectangle continuously
cv::Point pt; pt.x = x; pt.y = y;
cv::Mat temp_img = img.clone();
rectangle(temp_img, cor1, pt, cv::Scalar(0, 0, 255));
cv::imshow("Original", temp_img);
}
else if (event == cv::EVENT_MOUSEMOVE) //tracking mouse movement
{
std::cout << "Mouse moving over the window - position (" << x << ", " << y << ")" << std::endl;
}
if (leftButtonDown == true && leftButtonUp == true) //when the selection is done
{
rect.width = abs(cor1.x - cor2.x);
rect.height = abs(cor1.y - cor2.y);
rect.x = cv::min(cor1.x, cor2.x);
rect.y = cv::min(cor1.y, cor2.y);
cv::Mat cutTempImg(img, rect); //Selecting a ROI(region of interest) from the original img
cv::namedWindow("Cut Temporary Image");
cv::imshow("Cut Temporary Image", cutTempImg); //showing the cropped image
leftButtonDown = false;
leftButtonUp = false;
}
}
int main(){
img = cv::imread("image.jpg");
cv::namedWindow("Original");
cv::imshow("Original", img);
cv::setMouseCallback("Original", mouseCall); //setting the mouse callback for selecting the region with mouse
while (char(cv::waitKey(1) != 'q')) //waiting for the 'q' key to finish the execution
{
}
return 0;
}
And it is working fine. Now I want to make same code, with using class.(OOP)
But cv::setMouseCallback function is not letting me do that.
Can any one help me fix this?
My second code :
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#include <string>
class ResizeImage {
cv::Mat img;
cv::Point cor1, cor2;
cv::Rect rect;
std::string name;
public:
void setImg(cv::Mat img) { this->img = img; };
cv::Mat getImg() { return img; };
void setRect();
int getCoordinates1X() { return cor1.x; };
int getCoordinates1Y() { return cor1.y; };
int getCoordinates2X() { return cor2.x; };
int getCoordinates2Y() { return cor2.y; };
void setCoordinates1(int x, int y) { this->cor1.x = x; this->cor1.y = y; };
void setCoordinates2(int x, int y) { this->cor2.x = x; this->cor2.y = y; };
void mouseCall(int event, int x, int y, int flags, void* param);
void showImgOriginal();
void setImgName(std::string name) { this->name = name; };
std::string getImgName() { return name; };
};
void ResizeImage :: showImgOriginal() {
cv::namedWindow(name, CV_WINDOW_AUTOSIZE);
cv::imshow(name, img);
};
void ResizeImage::setRect() {
rect.width = abs(cor1.x - cor2.x);
rect.height = abs(cor1.y - cor2.y);
rect.x = cv::min(cor1.x, cor2.x);
rect.y = cv::min(cor1.y, cor2.y);
}
void ResizeImage::mouseCall(int event, int x, int y, int flags, void* param) {
if (event == cv::EVENT_LBUTTONDOWN) //finding first corner
{
leftButtonDown = true; setCoordinates1(x,y); std::cout << "Corner 1: " << getCoordinates1X()<<" "<<getCoordinates1Y() << std::endl;
}
if (event == cv::EVENT_LBUTTONUP) {
if (abs(x - cor1.x)>20 && abs(y - cor1.y)>5) //finding second corner and checking whether the region is too small
{
leftButtonUp = true; setCoordinates2(x, y); std::cout << "Corner 2: " << getCoordinates2X() << " " << getCoordinates2Y() << std::endl;
}
else { std::cout << "Select more than 5 pixels" << std::endl; }
}
if (leftButtonDown == true && leftButtonUp == false) //when the left button is down
{
cv::Point pt; pt.x = x; pt.y = y;
cv::Mat temp_img = img.clone();
rectangle(temp_img, cor1, pt, cv::Scalar(0, 0, 255)); //drawing a rectangle continuously
cv::imshow("Original", temp_img);
}
else if (event == cv::EVENT_MOUSEMOVE) //tracking mouse movement
{
std::cout << "Mouse moving over the window - position (" << x << ", " << y << ")" << std::endl;
}
if (leftButtonDown == true && leftButtonUp == true) //when the selection is done
{
setRect();
cv::Mat cutTempImg(img, rect); //Selecting a ROI(region of interest) from the original img
cv::namedWindow("Cut Temporary Image");
cv::imshow("Cut Temporary Image", cutTempImg); //showing the cropped image
leftButtonDown = false;
leftButtonUp = false;
}
}
int main(){
cv::Mat img = cv::imread("image.jpg");
ResizeImage img_;
img_.setImg(img);
img_.setImgName("original");
img_.showImgOriginal();
cv::setMouseCallback(img_.getImgName(),img_.mouseCall());
while (char(cv::waitKey(1) != 'q')) //waiting for the 'q' key to finish the execution
{
}
return 0;
}
Code after changes :
//Program is loading image, and showing it to user.
//User can use mouse to make a rectangle and cut the loaded image.
//Command line is tracking mouse movements and the coordinates of the rectangle.
//User can end the program using 'q'.
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#include <string>
bool leftButtonDown = false, leftButtonUp = false; //flags for mouse clicks
class ResizeImage {
cv::Mat img; //image to process
cv::Point cor1, cor2; //coordinates of selected rectangle
cv::Rect rect; //rectangle
std::string name; //windows name
public:
//////////////////////////////////////////////////////////////////////////////
ResizeImage() { std::cout << "Starting..."<<std::endl; }; //Constructor/Destructor
~ResizeImage() { std::cout << "Ending..." << std::endl; };
//////////////////////////////////////////////////////////////////////////////
void setImg(cv::Mat img) { this->img = img; };
void setImgName(std::string name) { this->name = name; }; //set functions
void setRect();
void setCoordinates1(int x, int y) { this->cor1.x = x; this->cor1.y = y; };
void setCoordinates2(int x, int y) { this->cor2.x = x; this->cor2.y = y; };
//////////////////////////////////////////////////////////////////////////////
int getCoordinates1X() { return cor1.x; }; //getfunctions
int getCoordinates1Y() { return cor1.y; };
int getCoordinates2X() { return cor2.x; };
int getCoordinates2Y() { return cor2.y; };
cv::Mat getImg() { return img; };
std::string getImgName() { return name; };
//////////////////////////////////////////////////////////////////////////////
static void mouseCall(int event, int x, int y, int flags, void* param); //static function
//////////////////////////////////////////////////////////////////////////////
void showImgOriginal(); //show function (priting image)
//////////////////////////////////////////////////////////////////////////////
};
void ResizeImage :: showImgOriginal() { //showing image
cv::namedWindow(name, CV_WINDOW_AUTOSIZE);
cv::imshow(name, img);
};
void ResizeImage::setRect() { //calculating selected rectangle
rect.width = abs(cor1.x - cor2.x);
rect.height = abs(cor1.y - cor2.y);
rect.x = cv::min(cor1.x, cor2.x);
rect.y = cv::min(cor1.y, cor2.y);
}
void ResizeImage::mouseCall(int event, int x, int y, int flags, void* param) {
if (event == cv::EVENT_LBUTTONDOWN) //finding first corner
{
leftButtonDown = true; ((ResizeImage*)param)->cor1.x = x; ((ResizeImage*)param)->cor1.y = y; //saving coordinates
std::cout << "Corner 1: " << ((ResizeImage*)param)->cor1.x << " " << ((ResizeImage*)param)->cor1.y << std::endl; //printing coordinates
}
if (event == cv::EVENT_LBUTTONUP) {
if (abs(x - ((ResizeImage*)param)->cor1.x)>20 && abs(y - ((ResizeImage*)param)->cor1.y)>10) //finding second corner and checking whether the region is too small
{
leftButtonUp = true; ((ResizeImage*)param)->cor2.x = x; ((ResizeImage*)param)->cor2.y = y; //saving coordinates
std::cout << "Corner 2: " << ((ResizeImage*)param)->cor2.x << " " << ((ResizeImage*)param)->cor2.y << std::endl; //printing coordinates
}
else { std::cout << "Select more than 10 pixels" << std::endl; } //warning if region is too small
}
if (leftButtonDown == true && leftButtonUp == false) //when the left button is down
{
cv::Point pt; pt.x = x; pt.y = y;
cv::Mat temp_img = ((ResizeImage*)param)->img.clone();
rectangle(temp_img, ((ResizeImage*)param)->cor1, pt, cv::Scalar(0, 0, 255)); //drawing a rectangle continuously
}
else if (event == cv::EVENT_MOUSEMOVE) //tracking mouse movement
{
std::cout << "Mouse moving over the window - position (" << x << ", " << y << ")" << std::endl;
}
if (leftButtonDown == true && leftButtonUp == true) //when the selection is done
{
((ResizeImage*)param)->setRect();
cv::Mat cutTempImg(((ResizeImage*)param)->img, ((ResizeImage*)param)->rect); //Selecting a ROI(region of interest) from the original img
cv::namedWindow("Cut Temporary Image");
cv::imshow("Cut Temporary Image", cutTempImg); //showing the cropped image
leftButtonDown = false;
leftButtonUp = false;
}
}
int main() {
cv::Mat img = cv::imread("image.jpg");
ResizeImage img_;
img_.setImg(img);
img_.setImgName("Original");
img_.showImgOriginal();
cv::setMouseCallback(img_.getImgName(),ResizeImage::mouseCall,&img_);
while (char(cv::waitKey(1) != 'q')) //waiting for the 'q' key to finish the execution
{
}
return 0;
}

Answer 1

If you want to use a class method as a callback, you should indeed declare the method as static. However, you also need to pass an object to the callback to be able to access non static members of your class such as cor1 or cor2.
Here is a minimal example of how you can achieve this:
class Call {
public:
Call(int i) : a(i){};
int a;
static void mouse(int event, int x, int y, int flags, void* param) {
std::cout << ((Call*)param)->a << std::endl;
}
};
cv::namedWindow("Call");
Call call(10);
cv::setMouseCallback("Call", Call::mouse, &call);
cv::imshow("Call", cv::Mat(100, 100, CV_8U, cv::Scalar(0)));
cv::waitKey();
I create a Call object and use its mouse method as the window callback while still passing the object to the call back.

Answer 2

You should make the function static:
static void mouseCall(int event, int x, int y, int flags, void* param);
and then:
cv::setMouseCallback(img_.getImgName(),ResizeImage::mouseCall);