c4droid exemple opengl + SDL "window'

// Headerphile.com OpenGL Tutorial part 1
// A Hello World in the world of OpenGL ( creating a simple windonw and setting background color )
// Source code is an C++ adaption / simplicication of : https://www.opengl.org/wiki/Tutorial1:_Creating_a_Cross_Platform_OpenGL_3.2_Context_in_SDL_(C_/_SDL)
// Compile : clang++ main.cpp -lGL -lSDL2 -std=c++11 -o Test

// C++ Headers
//WINDOW in sdl2 with opengl write in c4droid on tablet lenovo
//to compile use sdl2 parametrs
//
#include <string>
#include <iostream>

// OpenGL / glew Headers
#define GL3_PROTOTYPES 1
//#include <GL/glew.h>
#include <iostream>
// SDL2 Headers
#include <SDL2/SDL.h>

#include <EGL/egl.h>
#include <GLES/gl.h>

#include <android/sensor.h>
#include <android/log.h>
#include <android_native_app_glue.h>

#define __glPi 3.14159265358979323846
//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

// Our SDL_Window ( just like with SDL2 wihout OpenGL)
SDL_Window *mainWindow;

// Our opengl context handle
SDL_GLContext mainContext;


namespace gl {
   
void glutMainLoop(void)
{
 

  for (;;);
}

void draw()
{
    // Cover with blue and update
                    glClearColor(0.0, 0.0, 1.0, 1.0);
                    glClear(GL_COLOR_BUFFER_BIT);
                    SDL_GL_SwapWindow(mainWindow);
}
bool initGL()
{
    //Initialize Projection Matrix
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();

    //Initialize Modelview Matrix
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    //Initialize clear color
    glClearColor( 0.f, 0.f, 0.f, 1.f );

    //Check for error
    GLenum error = glGetError();
    if( error != GL_NO_ERROR )
    {
      
        return false;
    }

    return true;
}

};
using namespace gl;


std::string programName = "Headerphile SDL2 - OpenGL thing";



namespace SDL {
   
void CheckSDLError(int line);

bool SetOpenGLAttributes()
{
    // Set our OpenGL version.
    // SDL_GL_CONTEXT_CORE gives us only the newer version, deprecated functions are disabled
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

    // 3.2 is part of the modern versions of OpenGL, but most video cards whould be able to run it
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);

    // Turn on double buffering with a 24bit Z buffer.
    // You may need to change this to 16 or 32 for your system
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

    return true;
}
bool Init()
{

    // Initialize SDL's Video subsystem
    if (SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        std::cout << "Failed to init SDL\n";
        return false;
    }

    // Create our window centered at 512x512 resolution
    mainWindow = SDL_CreateWindow(programName.c_str(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_OPENGL );
   

    // Check that everything worked out okay
    if (!mainWindow)
    {
        std::cout << "Unable to create window\n";
    CheckSDLError(__LINE__);
        return false;
    }

    // Create our opengl context and attach it to our window
    mainContext = SDL_GL_CreateContext(mainWindow);
      if( gl::initGL() == false )
    {
        return false;
    }

    SetOpenGLAttributes();

    // This makes our buffer swap syncronized with the monitor's vertical refresh
    SDL_GL_SetSwapInterval(1);

    // Init GLEW
    // Apparently, this is needed for Apple. Thanks to Ross Vander for letting me know
    #ifndef __APPLE__
    //glewExperimental = GL_TRUE;
    //glewInit();
    #endif
   
    return true;
}




   

void Cleanup()
{
    // Delete our OpengL context
    SDL_GL_DeleteContext(mainContext);

    // Destroy our window
    SDL_DestroyWindow(mainWindow);

    // Shutdown SDL 2
    SDL_Quit();
}

void CheckSDLError(int line = -1)
{
    std::string error = SDL_GetError();

    if (error != "")
    {
        std::cout << "SLD Error : " << error << std::endl;

        if (line != -1)
            std::cout << "\nLine : " << line << std::endl;

        SDL_ClearError();
    }
}

void PrintSDL_GL_Attributes()
{
    int value = 0;
    SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &value);
    std::cout << "SDL_GL_CONTEXT_MAJOR_VERSION : " << value << std::endl;

    SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &value);
    std::cout << "SDL_GL_CONTEXT_MINOR_VERSION: " << value << std::endl;
}
};
using namespace SDL;

int main(int argc, char *argv[])
{
    if (!Init())
        return -1;

draw();
glutMainLoop();
    //RunGame();

    Cleanup();

    return 0;
}