Putting image into a Window in x11 - image

Question

I have a QR code in .JPG format. I load it using OpenCV 3.4.4. Now, I create a new X11 window using XCreateSimpleWindow(). Then, I will resize the QR image to that of this new window.
Next, I want to put this resized QR code into the window. I tried using XPutImage(), but without any success, probably because I don't know the usage.
For using XPutImage(), I first took the image of the X11 window using XGetImage(); then obtained the pixel values of the QR image, then assigned that to the pixel value of the image obtained through XGetImage.
Once I had this XImage, I tried putting it to the window using XPutImage. But, it is still showing a black window.
There is no error in the terminal, but result is not as desired.
Any solution to this problem? Like, how to change the background of the window (X11) w.r.t a sample image, and using XPutImage()?
The code goes like this...
// Written by Ch. Tronche (http://tronche.lri.fr:8000/)
// Copyright by the author. This is unmaintained, no-warranty free software.
// Please use freely. It is appreciated (but by no means mandatory) to
// acknowledge the author's contribution. Thank you.
// Started on Thu Jun 26 23:29:03 1997
//
// Xlib tutorial: 2nd program
// Make a window appear on the screen and draw a line inside.
// If you don't understand this program, go to
// http://tronche.lri.fr:8000/gui/x/xlib-tutorial/2nd-program-anatomy.html
//
// compilation:
// g++ -o go qrinX11.cpp `pkg-config --cflags --libs opencv` -lX11
//
#include <opencv2/opencv.hpp>
#include "opencv2/opencv.hpp" // FOR OpenCV
#include <opencv2/core.hpp> // Basic OpenCV structures (cv::Mat)
#include <opencv2/videoio.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <bits/stdc++.h>
#include <X11/Xlib.h> // Every Xlib program must include this
#include <assert.h> // I include this to test return values the lazy way
#include <unistd.h> // So we got the profile for 10 seconds
#include <X11/Xutil.h>
#include <X11/keysym.h>
#include <X11/Xlib.h> // Every Xlib program must include this
#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <X11/extensions/Xcomposite.h>
#include <X11/extensions/Xfixes.h>
#include <X11/extensions/shape.h>
#define NIL (0) // A name for the void pointer
using namespace cv;
using namespace std;
int main()
{
XGCValues gr_values;
//GC gc;
XColor color, dummy;
Display *dpy = XOpenDisplay(NIL);
//assert(dpy);
//int screen = DefaultScreen(dpy);
// Get some colors
int blackColor = BlackPixel(dpy, DefaultScreen(dpy));
int whiteColor = WhitePixel(dpy, DefaultScreen(dpy));
// Create the window
Window w = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 0, 0,
200, 100, 0, whiteColor, blackColor);
// We want to get MapNotify events
XSelectInput(dpy, w, StructureNotifyMask);
XMapWindow(dpy, w);
// Wait for the MapNotify event
for(;;) {
XEvent e;
XNextEvent(dpy, &e);
if (e.type == MapNotify)
break;
}
Window focal = w;
XWindowAttributes gwa;
XGetWindowAttributes(dpy, w, &gwa);
int wd1 = gwa.width;
int ht1 = gwa.height;
XImage *image = XGetImage(dpy, w, 0, 0 , wd1, ht1, AllPlanes, ZPixmap);
unsigned long rm = image->red_mask;
unsigned long gm = image->green_mask;
unsigned long bm = image->blue_mask;
Mat img(ht1, wd1, CV_8UC3); // OpenCV Mat object is initilaized
Mat scrap = imread("qr.jpg");//(wid, ht, CV_8UC3);
resize(scrap, img, img.size(), CV_INTER_AREA);
for (int x = 0; x < wd1; x++)
for (int y = 0; y < ht1 ; y++)
{
unsigned long pixel = XGetPixel(image,x,y);
unsigned char blue = pixel & bm; // Applying the red/blue/green mask to obtain the indiv channel values
unsigned char green = (pixel & gm) >> 8;
unsigned char red = (pixel & rm) >> 16;
Vec3b color = img.at<Vec3b>(Point(x,y)); // Store RGB values in the OpenCV image
//color[0] = blue;
//color[1] = green;
//color[2] = red;
//img.at<Vec3b>(Point(x,y)) = color;
pixel = color[0];//&color[1]&color[2];
}
namedWindow("QR", CV_WINDOW_NORMAL);
imshow("QR", img);
cout << "herererere\n";
GC gc = XCreateGC(dpy, w, 0, NIL);
XPutImage(dpy, w, gc, image, 0, 0, wd1, ht1, wd1, ht1);
waitKey(0);
//sleep(3);
return 0;
}

Answer 1

Alright, solved it on my own. There was a silly mistake at changing the pixel value and updating it to the actual image and then putting it to the background of the window.
First use XPutPixel(), then use XPutImage()
Here is the final and correct method:
// compilation:
// g++ -o go qrinX11.cpp `pkg-config --cflags --libs opencv` -lX11
//
#include <opencv2/opencv.hpp>
#include "opencv2/opencv.hpp" // FOR OpenCV
#include <opencv2/core.hpp> // Basic OpenCV structures (cv::Mat)
#include <opencv2/videoio.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <bits/stdc++.h>
#include <X11/Xlib.h> // Every Xlib program must include this
#include <assert.h> // I include this to test return values the lazy way
#include <unistd.h> // So we got the profile for 10 seconds
#include <X11/Xutil.h>
#include <X11/keysym.h>
#include <X11/Xlib.h> // Every Xlib program must include this
#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <X11/extensions/Xcomposite.h>
#include <X11/extensions/Xfixes.h>
#include <X11/extensions/shape.h>
#define NIL (0) // A name for the void pointer
using namespace cv;
using namespace std;
int main()
{
XGCValues gr_values;
//GC gc;
XColor color, dummy;
Display *dpy = XOpenDisplay(NIL);
//assert(dpy);
//int screen = DefaultScreen(dpy);
// Get some colors
int blackColor = BlackPixel(dpy, DefaultScreen(dpy));
int whiteColor = WhitePixel(dpy, DefaultScreen(dpy));
// Create the window
Window w = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 0, 0,
200, 100, 0, whiteColor, blackColor);
// We want to get MapNotify events
XSelectInput(dpy, w, StructureNotifyMask);
XMapWindow(dpy, w);
// Wait for the MapNotify event
for(;;) {
XEvent e;
XNextEvent(dpy, &e);
if (e.type == MapNotify)
break;
}
Window focal = w;
XWindowAttributes gwa;
XGetWindowAttributes(dpy, w, &gwa);
int wd1 = gwa.width;
int ht1 = gwa.height;
XImage *image = XGetImage(dpy, w, 0, 0 , wd1, ht1, AllPlanes, ZPixmap);
unsigned long rm = image->red_mask;
unsigned long gm = image->green_mask;
unsigned long bm = image->blue_mask;
Mat img(ht1, wd1, CV_8UC3); // OpenCV Mat object is initilaized
Mat scrap = imread("qr.jpg");//(wid, ht, CV_8UC3);
resize(scrap, img, img.size(), CV_INTER_AREA);
for (int x = 0; x < wd1; x++)
for (int y = 0; y < ht1 ; y++)
{
unsigned long pixel = XGetPixel(image,x,y);
Vec3b color = img.at<Vec3b>(Point(x,y));
pixel = 65536 * color[2] + 256 * color[1] + color[0];
XPutPixel(image, x, y, pixel);
}
namedWindow("QR", CV_WINDOW_NORMAL);
imshow("QR", img);
GC gc = XCreateGC(dpy, w, 0, NIL);
XPutImage(dpy, w, gc, image, 0, 0, 0, 0, wd1, ht1);
waitKey(0);
return 0;
}

Answer 2

Simplicity is key, and improves performance (in this case):
//..
// Mat img(ht1, wd1, CV_8UC3); // OpenCV Mat object is initilaized
cv::Mat img(ht1, wd1, CV_8UC4, image->data); // initilaize with existing mem
Mat scrap = imread("qr.jpg");//(wid, ht, CV_8UC3);
cv::cvtColor(scrap,scrap,cv::COLOR_BGR2BGRA);
resize(scrap, img, img.size(), cv::INTER_AREA);
// .. and we can skip the for loops
namedWindow("QR", CV_WINDOW_NORMAL);
imshow("QR", img);
// .. etc