#include <windows.h>
#include <gl/gl.h>


LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);
void EnableOpenGL(HWND hWnd, HDC *hDC, HGLRC *hRC);
void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC);

HINSTANCE hInst;

int WINAPI WinMain(HINSTANCE hThisInst, HINSTANCE hPrevInst, LPSTR lpCmdLine, int nWinMode)
{
	WNDCLASS wc;
	HWND hWnd;
	MSG msg;
	int quit = 1;
	
	hInst = hThisInst;
	
	// register window class
	wc.style = CS_OWNDC;
	wc.lpfnWndProc = WndProc;
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hInstance = hInst;
	wc.hIcon = LoadIcon( NULL, IDI_APPLICATION );
	wc.hCursor = LoadCursor( NULL, IDC_ARROW );
	wc.hbrBackground = (HBRUSH)GetStockObject( WHITE_BRUSH );
	wc.lpszMenuName = NULL;
	wc.lpszClassName = "GLSample";
	RegisterClass( &wc );
	
	// create main window
	hWnd = CreateWindow( "GLSample", 
		                 "OpenGL Sample", 
		                 WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
		                 0, 0, 800, 600,
		                 NULL, NULL, hInst, NULL );
	
	ShowWindow( hWnd, nWinMode );
	UpdateWindow( hWnd );

	while( GetMessage( &msg, NULL, 0, 0 ) )
	{
		TranslateMessage( &msg );
		DispatchMessage( &msg );
	}
	
	return msg.wParam;
}
	
// Window Procedure
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	static HDC hDC;
	static HGLRC hRC;
	static int flag = 1;

	switch (message)
	{	
		case WM_CREATE:  EnableOpenGL( hWnd, &hDC, &hRC );
			                        return 0;
		case WM_PAINT :  // OpenGL animation code goes here	  
						 glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
			                         glClear( GL_COLOR_BUFFER_BIT );
						 if( flag )
						 {
							glBegin( GL_TRIANGLES );
							glColor3f( 1.0f, 0.0f, 0.0f ); glVertex2f( 0.0f, 1.0f );
							glColor3f( 0.0f, 1.0f, 0.0f ); glVertex2f( 0.87f, -0.5f );
							glColor3f( 0.0f, 0.0f, 1.0f ); glVertex2f( -0.87f, -0.5f );
							glEnd();
							flag = 0;
						 }
						 else
						 {
                                                        glBegin( GL_TRIANGLES );
							glColor3f( 0.0f, 0.0f, 1.0f ); glVertex2f( 0.0f, 1.0f );
							glColor3f( 0.0f, 1.0f, 0.0f ); glVertex2f( 0.87f, -0.5f );
							glColor3f( 1.0f, 0.0f, 0.0f ); glVertex2f( -0.87f, -0.5f );
							glEnd();
							flag = 1;
						 }
			                         SwapBuffers( hDC );	
					         return 0;
		case WM_DESTROY: DisableOpenGL( hWnd, hDC, hRC );
		                 PostQuitMessage(0);
		                 return 0;
		default:         return DefWindowProc( hWnd, message, wParam, lParam );
			
	}
	return 0;
}

// Enable OpenGL
void EnableOpenGL(HWND hWnd, HDC *hDC, HGLRC *hRC)
{
	PIXELFORMATDESCRIPTOR pfd;
	int format;
	
	// get the device context (DC)
	*hDC = GetDC( hWnd );
	
	// set the pixel format for the DC
	ZeroMemory( &pfd, sizeof( pfd ) );
	pfd.nSize = sizeof( pfd );
	pfd.nVersion = 1;
	pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
	pfd.iPixelType = PFD_TYPE_RGBA;
	pfd.cColorBits = 24;
	pfd.cDepthBits = 16;
	pfd.iLayerType = PFD_MAIN_PLANE;
	format = ChoosePixelFormat( *hDC, &pfd );
	SetPixelFormat( *hDC, format, &pfd );
	
	// create and enable the render context (RC)
	*hRC = wglCreateContext( *hDC );
	wglMakeCurrent( *hDC, *hRC );
	
}

// Disable OpenGL
void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC)
{
	wglMakeCurrent( NULL, NULL );
	wglDeleteContext( hRC );
	ReleaseDC( hWnd, hDC );
}