//This example uses/needs:
//ARB_buffer_storage (core in 4.4)
//glCopyBufferSubData (core in 3.1)

#include <SDL.h>
//#define GL_GLEXT_PROTOTYPES
#include <SDL_opengl.h>
#include <iostream>

using namespace std;

SDL_GLContext glRenderContext;
SDL_Window *mainWindow;

extern "C" typedef void (*PFNGLGENBUFFERSARBPROC)       (GLsizei n, GLuint  * buffers);
extern "C" typedef void (*PFNGLDELETEBUFFERSPROC)       (GLsizei n, const  GLuint  * buffers);
extern "C" typedef void (*PFNGLBINDBUFFERPROC)          (GLenum target, GLuint buffer);
extern "C" typedef void (*PFNGLBUFFERSTORAGEPROC)       (GLenum target, GLsizeiptr size, const void * data, GLbitfield flags);
extern "C" typedef void (*PFNGLCOPYBUFFERSUBDATAPROC)   (GLenum readTarget, GLenum writeTarget, GLintptr readOffset, GLintptr writeOffset, GLsizeiptr size);

static PFNGLGENBUFFERSARBPROC           glGenBuffers;
static PFNGLDELETEBUFFERSPROC           glDeleteBuffers;
static PFNGLBINDBUFFERPROC              glBindBuffer;
static PFNGLBUFFERSTORAGEPROC           glBufferStorage;
static PFNGLCOPYBUFFERSUBDATAPROC       glCopyBufferSubData;

int main(int argc, char* argv[])
{
    if (SDL_Init(SDL_INIT_VIDEO|SDL_INIT_TIMER) != 0) {
            cout << "Unable to initialize SDL: " << SDL_GetError() << endl;
    return -1;
    }

    mainWindow = SDL_CreateWindow(
        "An SDL2 window",                  //    window title
        SDL_WINDOWPOS_UNDEFINED,           //    initial x position
        SDL_WINDOWPOS_UNDEFINED,           //    initial y position
        300,                               //    width, in pixels
        300,                               //    height, in pixels
        SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE//  | SDL_WINDOW_FULLSCREEN
    );

    if (!mainWindow)
    {
            cout << "Error in SDL_CreateWindow: " << SDL_GetError() << endl;
            return -1;
    }

    //mesa/radeonsi only supports GL3.3 in Core
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
    //SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, GL_CONTEXT_FLAG_DEBUG_BIT);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

    glRenderContext = SDL_GL_CreateContext(mainWindow);
    if (!glRenderContext)
    {
        cout << "Error in SDL_GL_CreateContext: " << SDL_GetError() << endl;
        return -1;
    }
    SDL_GL_SetSwapInterval(1);

    glGenBuffers        = reinterpret_cast<PFNGLGENBUFFERSARBPROC>(     SDL_GL_GetProcAddress("glGenBuffers"));
    glDeleteBuffers     = reinterpret_cast<PFNGLDELETEBUFFERSPROC>(     SDL_GL_GetProcAddress("glDeleteBuffers"));
    glBindBuffer        = reinterpret_cast<PFNGLBINDBUFFERPROC>(        SDL_GL_GetProcAddress("glBindBuffer"));
    glBufferStorage     = reinterpret_cast<PFNGLBUFFERSTORAGEPROC>(     SDL_GL_GetProcAddress("glBufferStorage"));
    glCopyBufferSubData = reinterpret_cast<PFNGLCOPYBUFFERSUBDATAPROC>( SDL_GL_GetProcAddress("glCopyBufferSubData"));

    
    int bufferSize = 200 * 1024 * 1024;
    GLuint clientBufferId, serverBufferId;
    glGenBuffers(1, &clientBufferId);
    glBindBuffer(GL_ARRAY_BUFFER, clientBufferId);
    glBufferStorage(GL_ARRAY_BUFFER, bufferSize, 0, 0);

    glGenBuffers(1, &serverBufferId);
    glBindBuffer(GL_ARRAY_BUFFER, serverBufferId);
    glBufferStorage(GL_ARRAY_BUFFER, bufferSize, 0, 0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_COPY_READ_BUFFER,  clientBufferId);
    glBindBuffer(GL_COPY_WRITE_BUFFER, serverBufferId);
    glCopyBufferSubData(GL_COPY_READ_BUFFER, GL_COPY_WRITE_BUFFER, 0, 0, bufferSize);

    
    glDeleteBuffers(1, &clientBufferId);
    glDeleteBuffers(1, &serverBufferId);
    
    SDL_GL_DeleteContext(glRenderContext);
    SDL_DestroyWindow(mainWindow);
    SDL_Quit();

    return 0;
}