#include <windows.h>
#include <gl/gl.h>	//toto mozes mozna mat ako GL/gl.h keby daco

//forward deklaracie
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);

//main funkcia
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, 
				   LPSTR lpCmdLine, int iCmdShow)
{
	WNDCLASS wc;	//window class
	HWND hWnd;	//handle na window
	HDC hDC;	//handle na device context
	HGLRC hRC;	//handle na GL rendering context
	MSG msg;	//WinApi je message based paradigma, troska sa zda byt za vlasy pritiahnuta, ale je to okej
	BOOL quit = FALSE;
	float theta = 0.0f;	//premenna na zmenu stavu
	
	//zaregistrujeme window clasu
	wc.style = CS_OWNDC;
	wc.lpfnWndProc = WndProc;	//window procedura, ktoru sme zadefinovali nizsie
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hInstance = hInstance;	//handle instancu programu, ktoru namapujeme na samotny window
	wc.hCursor = LoadCursor( NULL, IDC_ARROW );
	wc.hbrBackground = (HBRUSH)GetStockObject( BLACK_BRUSH );
	wc.lpszMenuName = NULL;
	wc.lpszClassName = "OpenGL";	//class name windowu co spravime
	RegisterClass( &wc );		//zaregistrujeme na dalsie pouzivanie
	
	// vytvorime samotne okno
	hWnd = CreateWindow( 
		"OpenGL", "Opengl is great but DirectX rocks!!!", 	//class name a window title v tomto poradi to je 
									//definovane
		WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
		0, 0, 256, 256,		//sirka a vyska windowu tych 256, 256
		NULL, NULL, hInstance, NULL );	
	
	//namapujeme OpenGL na okno a na render/device context
	EnableOpenGL( hWnd, &hDC, &hRC );
	
	//tu prebieha hlavny uzol programu
	while ( !quit )
	{
		//zistime, ci su nejake messages v message loope, ak su, tak handle them, if not tak vykreslujeme
		if ( PeekMessage( &msg, NULL, 0, 0, PM_REMOVE )  )
		{
			//ak doslo quit message, tak vypne aplikaciu, ak nie, posunie message dalej
			if ( msg.message == WM_QUIT ) 
			{
				quit = TRUE;
			} 
			else 
			{
				TranslateMessage( &msg );
				DispatchMessage( &msg );
			}
		} 
		else 
		{
			//
			//sem ide veskery rendrovaci loop, toto vsetko z else mozes aj vymazat ak chces
			//a nahradit vlastnym :) (az na glClearColor a glClear, tie treba hocijak...a SwapBuffers)
			//
			glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );	//vymaz celeho framebufferu na nejaku solid farbu
								//vo formate RGBA...nemusi byt cierne, odporucam 
								//vyskusat aj cornflower blue na debugovacie ucely
								//R: 0.258824f G: 0.258824f B: 0.435294f A: 1.0f
			glClear( GL_COLOR_BUFFER_BIT );	//vymazeme color buffer (cize vsetko co sme nakreslili vo frame
							//neskor sa ti tu objavia aj ine parametre ako depth a stencil buffer
							//az budes robit normal a shadow mapping
			
			glPushMatrix();	//ulozime stav projekcnej matice
			glRotatef( theta, 0.0f, 0.0f, 1.0f );	//pootocime po X ovej osi o theta obrazec
			glBegin( GL_TRIANGLES );	//tymto prikazom povies OpenGL ze chces zacat vykreslovanie
			{				//trojuholnikov...existuje viacero typov, ako GL_LINES alebo
							//GL_POINTS alebo GL_TRIANDGLE_STRIP/GL_TRIANGLE_FAN
							//ale v ziadnom pripade nepouzi GL_QUAD...je to uz deprecated davno
				glColor3f( 1.0f, 0.0f, 0.0f );	//v OpenGL nastavujes vzdy dany stav, nez sa to vykona
								//cize tu mas nastavenu farbu pre dany vertex, ak robis
								//per vertex lighting ako v tomto pripade
				glVertex2f( 0.0f, 1.0f );	//tu si das vykreslit dany vertex s poziciami udanymi X a Y
				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();	//touto funkciou povies OpenGL ze si dokoncila vykreslovanie pre dany utvar
			glPopMatrix();	//obnovis stav projekcnej matice
			
			SwapBuffers( hDC );	//zamenis frontbuffer za backbuffer, kde sa ti zatial vsetko vykreslilo v pozadi
			
			theta += 1.0f;	//inkrementujes tetu :D
		}
	}
	
	//vycistis OpenGL a vypnes
	DisableOpenGL( hWnd, hDC, hRC );
	
	//explicitne zavres okno
	DestroyWindow( hWnd );
	
	return msg.wParam;
	
}

//window procedura
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	
	switch (message)
	{
		
	case WM_CREATE:
		return 0;
		
	case WM_CLOSE:
		PostQuitMessage( 0 );
		return 0;
		
	case WM_DESTROY:
		return 0;
		
	case WM_KEYDOWN:
		switch ( wParam )
		{
			//tu mozes definovat vstupy z klavesnice, napr VK_ENTER tusim na stlacenie entra
		case VK_ESCAPE:
			PostQuitMessage(0); //tu sa posle message na vypnutie okna
			return 0;
			
		}
		return 0;
	
	default:
		return DefWindowProc( hWnd, message, wParam, lParam );
			
	}
	
}

//funkcia na nastavenie opengl
void EnableOpenGL(HWND hWnd, HDC * hDC, HGLRC * hRC)
{
	PIXELFORMATDESCRIPTOR pfd;	//pixel format descriptor nam udava hlbku farieb a udava paletu
	int format;
	
	//ziskame device context z handlu na window
	*hDC = GetDC( hWnd );
	
	//tu sa nastavuje pixel format pre OpenGL
	ZeroMemory( &pfd, sizeof( pfd ) );
	pfd.nSize = sizeof( pfd );
	pfd.nVersion = 1;
	pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;	//doublebuffered pre znizenie flickeringu
											//support pre opengl
											//support pre priame kreslenie na window
	pfd.iPixelType = PFD_TYPE_RGBA;		//RGBA format farby, tusim tu si mozes dat aj ARGB32 a ine formaty, ako HSV a tak
	pfd.cColorBits = 24;		//kolko bitov chces na uchovavanie farieb...24 bity mas dost na zopar milionov farieb
	pfd.cDepthBits = 16;		//hlbka farby v bitoch per pixel
	pfd.iLayerType = PFD_MAIN_PLANE;	//netusim popravde co to robi, ale treba to
	format = ChoosePixelFormat( *hDC, &pfd );	//tu nam priradi system potrebny pixel format
	SetPixelFormat( *hDC, format, &pfd );		//ktory potom nastavime na ten window
	
	*hRC = wglCreateContext( *hDC ); //tu sa nam vytvori render context
	wglMakeCurrent( *hDC, *hRC );	//ktory hned priradime a zapneme
	
}

//Funkcia na uvolnenie contextu, a vypnutie okna
void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC)
{
	wglMakeCurrent( NULL, NULL );
	wglDeleteContext( hRC );
	ReleaseDC( hWnd, hDC );
}