SFML Thread does not works for window - multithreading

Question

I have simple code:
#include <SFML\Graphics.hpp>
sf::RenderWindow *mainWindow;
void changeMainWindowParameters()
{
while(mainWindow->isOpen())
{
sf::Event event;
while (mainWindow->pollEvent(event))
{
if(event.type == sf::Event::Closed)
{
mainWindow->close();
return;
}
}
mainWindow->clear();
mainWindow->draw(sf::CircleShape(50.0F, 30));
mainWindow->display();
}
}
int main()
{
mainWindow = new sf::RenderWindow(
sf::VideoMode(100, 100), "Window");
changeMainWindowParameters();
}
But if I want to do it with threads, it does not work as in previous example:
#include <SFML\Graphics.hpp>
sf::RenderWindow *mainWindow;
void changeMainWindowParameters()
{
while(mainWindow->isOpen())
{
sf::Event event;
while (mainWindow->pollEvent(event))
{
if(event.type == sf::Event::Closed)
{
mainWindow->close();
return;
}
}
mainWindow->clear();
mainWindow->draw(sf::CircleShape(50.0F, 30));
mainWindow->display();
}
}
int main()
{
mainWindow = new sf::RenderWindow(
sf::VideoMode(100, 100), "Window");
sf::Thread th(changeMainWindowParameters);
th.launch();
//code
th.wait();
}
I can't close the window/move it etc.
I want the program to do something (drawing images on this window etc.) and so I could close/move this window.
Where is wrong?

Answer 1

I solve this problem:
#include <SFML\Graphics.hpp>
#include <thread>
#include <iostream>
sf::RenderWindow *mainWindow = nullptr;
void changeMainWindowParameters()
{
if (mainWindow == nullptr)
mainWindow = new sf::RenderWindow(sf::VideoMode(100, 100), "Window");
while(mainWindow->isOpen())
{
sf::Event event;
while (mainWindow->pollEvent(event))
{
if(event.type == sf::Event::Closed)
{
mainWindow->close();
return;
}
}
mainWindow->clear();
mainWindow->draw(sf::CircleShape(50.0F, 30));
mainWindow->display();
}
}
int main()
{
sf::Thread th(changeMainWindowParameters);
th.launch();
for(;;)
std::cout << '.';
th.wait();
}
We must remember that the event loop (more precisely, the pollEvent or waitEvent function) must be called in the same thread that created the window.