SDL2 two windows in different threads - c++

Question

I am trying to create a process with two windows. Each window has a different thread for drawing. The problem is that when I run the program, after a random amount of time something goes wrong and gives me a segmentation fault. Here is my code:
main.cpp
std::thread *thr1 = new std::thread(thread_func);
std::thread *thr2 = new std::thread(thread_func);
thread.cpp:
Window *win = new Window(display_name, 1024, 768);
Renderer *rend = win->CreateRenderer();
Texture *pic = new Texture(rend, path);
while (!quit)
{
usleep (10000);
pic->DrawToWindow(src_rect,rect);
rend->SetColor(255,255,255,255);
rend->DrawLine(10,10,300,300,4);
}
delete pic;
delete rend;
delete win;
Window.cpp:
Window::Window(std::string &name, uint32_t w, uint32_t h, uint32_t x, uint32_t y)
: window(nullptr),
windowRect()
{
if (!SDL_WasInit(SDL_INIT_VIDEO))
{
PDEBUG("ERROR: SDL Was not inited please init platform first!\n");
return;
}
//Create Window
window = SDL_CreateWindow(name.c_str(), x, y, w, h, SDL_WINDOW_OPENGL);
if (window == nullptr)
{
PDEBUG("ERROR: SDL_CreateWindow() %s\n", SDL_GetError());
return;
}
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 6);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
}
Window::~Window()
{
if (window != nullptr)
{
SDL_DestroyWindow(window);
window = nullptr;
}
}
void
Window::Flush()
{
SDL_GL_SwapWindow(window);
}
Renderer*
Window::CreateRenderer()
{
return new Renderer(this);
}
Renderer.cpp:
Renderer::Renderer(Window *win)
: window(win),
render(nullptr),
context()
{
if (win == nullptr)
{
PDEBUG("ERROR: Window is NULL\n");
return;
}
//Create Renderer
render = SDL_CreateRenderer(win->window, -1, SDL_RENDERER_ACCELERATED);
if (render == nullptr)
{
PDEBUG("ERROR: SDL_CreateRenderer(): %s\n", SDL_GetError());
return;
}
//Create Window OpenGL Context
//context = SDL_GL_CreateContext(win->window);
//if (SDL_GL_MakeCurrent(window->window, context) != 0)
// PDEBUG("ERROR: SDL_GL_MakeCurrent() %s\n", SDL_GetError());
Clear();
}
Renderer::~Renderer()
{
if (render != nullptr)
{
SDL_DestroyRenderer(render);
render = nullptr;
//SDL_GL_DeleteContext(context);
}
}
bool
Renderer::DrawLine(int xStart, int yStart, int xEnd, int yEnd, int width)
{
//if (SDL_GL_MakeCurrent(window->window, context) != 0)
// PDEBUG("ERROR: SDL_GL_MakeCurrent() %s\n", SDL_GetError());
//}
glLineWidth(width);
if (SDL_RenderDrawLine(render, xStart, yStart, xEnd, yEnd) < 0)
{
PDEBUG("ERROR: SDL_RenderDrawLine() %s\n", SDL_GetError());
return false;
}
return true;
}
Do I have to draw in only one thread for two windows, use synchronization to drawing, or use SDL_Thread for threads?

Answer 1

Did i have to draw in only one thread for two windows
Yes.
From the SDL2 threading documentation:
NOTE: You should not expect to be able to create a window, render, or receive events on any thread other than the main one. For platform-specific exceptions or complicated options ask on the mailing list or forum.

Answer 2

Hello I found a solution for 2 windows in different threads.
Here is example:
static bool quit = false;
void
thread_function(SDL_Window* win, SDL_Renderer *rend)
{
SDL_Event event;
while(!quit)
{
//DO THINGS with renderer and window. (Draw, Fill, Present Textures and others)
SDL_PollEvent(&event);
}
}
For Every thread you need to poll event because window events also are in Event Query.