我正在观看3DBuzz.com提供的一系列OpenGL教程。这些教程是使用SDL 1制作的，但现在我使用的是SDL2。我已经尝试将所有内容迁移到最新版本的SDL2，所有内容都已正确链接，整个库都正常工作。我认为错误出现在第140行，在原始视频中是以下调用：SDL_GL_SwapBuffers()，但现在在SDL2中，如您所知，已更改为SDL_GL_SwapWindow()，但我无法调用变量（screen），因为它位于main函数中。这会引发错误，我不知道如何解决此问题。因此，对于SDL2Maven，我希望您能帮助我。以下是完整的代码，您可以告诉我哪里做错了：

#include "SDL.h"
#include <stdio.h>
#include <stdlib.h>

#define GLUT_DISABLE_ATEXIT_HACK

#if defined (_WIN32) || defined(_WIN64)
    #define WIN32_LEAN_AND_MEAN
    #include <windows.h>
#endif // WIN32

#if defined(__APPLE__) && defined(__MACH__)
    #include <OpenGL/gl.h>
    #include <OpenGL/glu.h>
#else
    #include <GL/gl.h>
    #include <GL/glut.h>
#endif // defined

const GLsizei windowWidth = 500;
const GLsizei windowHeight = 500;

GLfloat cubeRotateX = 45.0f;
GLfloat cubeRotateY = 45.0f;

const Uint8 *keys = NULL;

GLvoid establishProjectionMatrix(GLsizei width, GLsizei height)
{
    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    gluPerspective(50.0f, (GLfloat)width / (GLfloat)height, 0.1f, 200.0f);
}

GLvoid initGL(GLsizei width, GLsizei height)
{
    establishProjectionMatrix(width, height);

    glShadeModel(GL_SMOOTH);

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);

    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
    glEnable(GL_PERSPECTIVE_CORRECTION_HINT);

}

GLvoid displayFPS(GLvoid)
{
    static long lastTime = SDL_GetTicks();
    static long loops = 0;
    static GLfloat fps = 0.0f;

    int newTime = SDL_GetTicks();

    if (newTime - lastTime > 100)
    {
        float newFPS = (float)loops / float(newTime - lastTime) * 1000.0f;

        fps = (fps + newFPS) / 2.0f;

        char title[80];
        printf(title, "OpenGL Demo - %2f", fps);

        lastTime = newTime;

        loops = 0;
    }

    loops++;

}

GLvoid drawScene(GLvoid)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glTranslatef(0, 0, -5.0f);
    glRotatef(cubeRotateX, 1, 0, 0);
    glRotatef(cubeRotateY, 0, 1, 0);

    //draw cube
    glBegin(GL_QUADS);
        //top face
        glColor3f(1.0f, 0.5f, 0.0f);
        glVertex3f(1.0f,  1.0f, -1.0f);
        glVertex3f(-1.0f, 1.0f, -1.0f);
        glVertex3f(-1.0f, 1.0f,  1.0f);
        glVertex3f(1.0f,  1.0f,  1.0f);

        //bottom face
        glColor3f(0.0f, 1.0f, 0.0f);
        glVertex3f( 1.0f, -1.0f, -1.0f);
        glVertex3f(-1.0f, -1.0f, -1.0f);
        glVertex3f(-1.0f, -1.0f,  1.0f);
        glVertex3f( 1.0f, -1.0f,  1.0f);

        //front face
        glColor3f(1.0f, 0.0f, 0.0f);
        glVertex3f( 1.0f,  1.0f,  1.0f);
        glVertex3f(-1.0f,  1.0f,  1.0f);
        glVertex3f(-1.0f, -1.0f,  1.0f);
        glVertex3f( 1.0f, -1.0f,  1.0f);

          //back face
        glColor3f(1.0f, 1.0f, 0.0f);
        glVertex3f( 1.0f,  1.0f,  -1.0f);
        glVertex3f(-1.0f,  1.0f,  -1.0f);
        glVertex3f(-1.0f, -1.0f,  -1.0f);
        glVertex3f( 1.0f, -1.0f,  -1.0f);

          //left face
        glColor3f(0.0f, 0.0f, 1.0f);
        glVertex3f(-1.0f,  1.0f,   1.0f);
        glVertex3f(-1.0f,  1.0f,  -1.0f);
        glVertex3f(-1.0f, -1.0f,  -1.0f);
        glVertex3f(-1.0f, -1.0f,   1.0f);

          //right face
        glColor3f(1.0f, 0.0f, 1.0f);
        glVertex3f( 1.0f,  1.0f,  1.0f);
        glVertex3f( 1.0f,  1.0f,  1.0f);
        glVertex3f( 1.0f, -1.0f,  1.0f);
        glVertex3f( 1.0f, -1.0f,  1.0f);
    glEnd();

    glFlush();

    //SDL_GL_SwapBuffers(); here is supposed to replace with SDL_GL_SwapWindow() but if a put the window (screen)

    displayFPS();
}

GLboolean checkKeys(GLvoid)
{
    static long lastTime =  SDL_GetTicks();

    const GLfloat speed = 1.0f;
    const long updateTime = 10;

    if (keys[SDLK_ESCAPE])
        return true;

    long newTime = SDL_GetTicks();

    if (newTime - lastTime > updateTime)
    {
        if(keys[SDLK_LEFT])
        cubeRotateY -= speed;
        if(keys[SDLK_RIGHT])
        cubeRotateY += speed;
        if(keys[SDLK_UP])
        cubeRotateX -= speed;
        if(keys[SDLK_DOWN])
        cubeRotateX += speed;
    }

    return false;

}

int main(int argc, char **argv)
{

    SDL_Window *screen = SDL_CreateWindow("OpenGL test",20, 20, windowWidth, windowHeight, SDL_WINDOW_OPENGL);


    if ( SDL_Init(SDL_INIT_VIDEO) < 0 )
    {
        fprintf(stderr, "Unable to initialize SDL %s", SDL_GetError());
        exit(1);
    }

    if ( SDL_GetWindowSurface(screen))
    {
        fprintf(stderr, "Unable to create openGL scene %s", SDL_GetError());
        exit(2);
    }

    initGL(windowWidth, windowHeight);

    int done = 0;

    while ( !done )
    {
        drawScene();

        SDL_Event event;

        while( SDL_PollEvent(&event) )
        {
            if ( event.type == SDL_QUIT )
                done = 1;

            keys = SDL_GetKeyboardState(NULL);
        }

        if(checkKeys()){
            done = 1;
        }

    }

    SDL_Quit();

    return 1;
}