Desplay error when using SDL2 to draw a Qt widget

NickYX

Recently, I am going to create a game editor for my game written by SDL2.
I search around about how to mix SDL2 with Qt.
Finally, I got it run successfully but with a strange display error:

Error Window Picture

Here are three code files: main.cpp, widget.cpp, widget.h.
widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <QWidget>
#include <QPaintEvent>
class SDL2Widget : public QWidget
{
    Q_OBJECT
public:
    SDL2Widget(QWidget* parent=0);
    ~SDL2Widget();
protected:
    void paintEvent(QPaintEvent* event);

private:
    SDL_Window *window;
    SDL_Renderer *render;
    SDL_Surface *surface;
    SDL_Texture *texture;
};

#endif // WIDGET_H

widget.cpp

#include "widget.h"

SDL2Widget::SDL2Widget(QWidget* parent) : QWidget(parent) {
  /* SDL2 */
  SDL_Init(SDL_INIT_EVERYTHING);
  /* Create SDL_Window from QWidget by using its winid */
  window = SDL_CreateWindowFrom((void*)this->winId());
  /* Init SDL2 Image */
  IMG_Init(IMG_INIT_JPG);
  /* load picture and create a SDL surface */
  surface = IMG_Load("demo.jpg");

  /* Creat a SDL2 render from SDL window*/
  render = SDL_CreateRenderer(
      window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
}

SDL2Widget::~SDL2Widget() {
  SDL_DestroyTexture(texture);
  SDL_DestroyRenderer(render);
}

/* Put SDL render staff in paintEvent */
void SDL2Widget::paintEvent(QPaintEvent* event) {
  /* Create a texture */
  texture = SDL_CreateTextureFromSurface(render, surface);
  /* Clear render content*/
  SDL_RenderClear(render);
  /* Copy texture to render */
  SDL_RenderCopy(render, texture, NULL, NULL);
  /* Render on window */
  SDL_RenderPresent(render);
}

main.cpp

#include <QApplication>
#include <QLayout>
#include <QPushButton>

#include "widget.h"

int main(int argc, char* argv[]) {
  QApplication app(argc, argv);
  QBoxLayout* layout = new QBoxLayout(QBoxLayout::TopToBottom);
  SDL2Widget* sdlWidget = new SDL2Widget();
  QPushButton* button = new QPushButton("Button");
  layout->addWidget(sdlWidget);
  layout->addWidget(button);

  QWidget w;
  w.setLayout(layout);

  w.show();
  w.resize(640, 400);

  return app.exec();
}

I guess it may be a thread problem?

NickYX

Finally, I give up using SDL to render on a QT Widget.
Instead, I choose to create a QtWindow from a window created by SDL by using QWindow::fromWinId(WId id).
Under windows, the window handle: HWND of an SDL window can be obtained from the SDL_SysWMinfo.win.window.

And to avoid thread problems. The SDL window should be inited and created in a std::thread before the QApplication a(argc, argv);