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SDL_Window *window = SDL_CreateWindowFrom((void*)this->winId())

virtual void QWidget::paintEvent(QPaintEvent* event);

/*
    File   : SDL2Widget.h
    Author : hubenchang0515@outlook.com
    Blog   : www.kurukurumi.com
*/
 
#ifndef SDL2WIDGET_H
#define SDL2WIDGET_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

/*
    File   : SDL2Widget.cpp
    Author : hubenchang0515@outlook.com
    Blog   : www.kurukurumi.com
*/
 
#include <SDL2Widget.h>
 
SDL2Widget::SDL2Widget(QWidget* parent):QWidget(parent)
{
    /* SDL2初始化 */
    SDL_Init(SDL_INIT_EVERYTHING);
    /* 把QWidget转换为SDL_Window */
    window = SDL_CreateWindowFrom((void*)this->winId());
    /* SDL2 Image初始化 */
    IMG_Init(IMG_INIT_PNG);
    /* 加载图片，创建surface */
    surface = IMG_Load("demo.jpg");
}
 
SDL2Widget::~SDL2Widget()
{
 
}
 
/* 绘图操作必须在paintEvent事件里进行 */
void SDL2Widget::paintEvent(QPaintEvent* event)
{
    /* 在window上创建一个render */
    render = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED 
                        | SDL_RENDERER_PRESENTVSYNC);
    /* 创建一个texture */
    texture = SDL_CreateTextureFromSurface(render, surface);
    /* 清空render的内容 */
    SDL_RenderClear(render);
    /* 将texture复制到render上 */
    SDL_RenderCopy(render, texture, NULL, NULL);
    /* 将render显示到window上 */
    SDL_RenderPresent(render);
    SDL_RenderPresent(render); //我的电脑上，需要调用两次才能显示出来，原因不明
    /* 销毁render和texture，释放内存 */
    SDL_DestroyTexture(texture);
    SDL_DestroyRenderer(render);
 
}

/*
    File   : main.cpp
    Author : hubenchang0515@outlook.com
    Blog   : www.kurukurumi.com
*/
 
#include <QApplication>
#include <SDL2Widget.h>
#include <QLayout>
#include <QPushButton>
 
int main(int argc,char* argv[])
{
    QApplication app(argc,argv);
    QVBoxLayout* layout = new QVBoxLayout;
    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);
    QObject::connect(button,&QPushButton::clicked,
        sdlWidget,(void(SDL2Widget::*)(void))&SDL2Widget::repaint);
    return app.exec();
}

#include "mainwindow.h"
#include <QApplication>
#include <SDL2/SDL.h>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window* window = SDL_CreateWindowFrom((void*)w.ptr_gfx->winId());
    SDL_Renderer* render = SDL_CreateRenderer(window, -1, SDL_RENDERER_SOFTWARE);

    SDL_SetRenderDrawColor(render, 255, 0, 0, 255);
    SDL_RenderFillRect(render, NULL);
    SDL_RenderPresent(render);

    return a.exec();

    SDL_DestroyWindow(window);
    SDL_DestroyRenderer(render);
    SDL_Quit();
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ptr_gfx = ui->gfx;
    ui->gfx->setUpdatesEnabled(false);
}

MainWindow::~MainWindow()
{
    delete ui;
}

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    Ui::MainWindow *ui;
    QWidget* ptr_gfx;
};

#endif // MAINWINDOW_H

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QWidget" name="gfx" native="true">
    <property name="geometry">
     <rect>
      <x>20</x>
      <y>10</y>
      <width>191</width>
      <height>131</height>
     </rect>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>400</width>
     <height>20</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>