Does anyone know if I can draw on the image window using CImg and C++?

Question

I'm trying to get user input from the image window using the CImg library and C++. I want the user to draw a shape on the displayed window so I can save and use their data later, but I haven't found anything that resembles what I am trying to do. I'm just wondering if it is possible.

Answer 1

Basically, you need to set up to capture mouse-clicks like this:

#include <iostream>
#include "CImg.h"

using namespace cimg_library;

int main(int argc,char **argv) {

  // Load a background image
  CImg<unsigned char> src("image.jpg");

  unsigned char red[]={255,0,0};

  // Display it
  CImgDisplay disp(src,"Image");

  // Remember position of last mouse click
  int prev_x = -1;
  int prev_y = -1;

  // Main display loop
  while (!disp.is_closed() && !disp.is_keyQ() && !disp.is_keyESC()) {

    CImgDisplay::wait(disp);

    // When clicking on the image
    if (disp.button()) {
       int x = disp.mouse_x();
       int y = disp.mouse_y();
       std::cout << "x: " << x << ", y: " << y << std::endl;
       if(prev_x!=-1){
           src.draw_line(prev_x,prev_y,x,y,red).display(disp);
       }
       prev_x = x;
       prev_y = y;
    }
  }
}

You would then append the x,y positions to an std::vector each time the user clicks, in order to remember them. Presumably, you would then want to check with each click, whether the current click position was within a few pixels of the start position and if so, close the polygon, fill it and add it to some list of shapes.