//openglutil.cpp

//初始化OpenGL

void InitializeOpenGL(int width, int height) 
{  
    g_hDC = GetDC(g_hWnd);								// This sets our global HDC
														// We don't free this hdc until the end of our program
    if (!bSetupPixelFormat(g_hDC))						// This sets our pixel format/information
        PostQuitMessage (0);							// If there's an error, quit

    g_hRC = wglCreateContext(g_hDC);					// This creates a rendering context from our hdc
    wglMakeCurrent(g_hDC, g_hRC);						// This makes the rendering context we just created the one we want to use

	glEnable(GL_TEXTURE_2D);							// Enables Texture Mapping
	glEnable(GL_DEPTH_TEST);							// Enables Depth Testing

	SizeOpenGLScreen(width, height);					// Setup the screen translations and viewport
}

//改變窗口大小
void SizeOpenGLScreen(int width, int height)			// Initialize The GL Window
{
	if (height==0)										// Prevent A Divide By Zero error
	{
		height=1;										// Make the Height Equal One
	}

	glViewport(0,0,width,height);						// Make our viewport the whole window
														// We could make the view smaller inside
														// Our window if we wanted too.
														// The glViewport takes (x, y, width, height)
														// This basically means, what our our drawing boundries

	glMatrixMode(GL_PROJECTION);						// Select The Projection Matrix
	glLoadIdentity();									// Reset The Projection Matrix

														// Calculate The Aspect Ratio Of The Window
														// The parameters are:
														// (view angle, aspect ration of the width to the height, 
														//  The closest distance to the camera before it clips, 
				  // FOV		// Ratio				//  The farthest distance before it stops drawing)
	gluPerspective(45.0f,(GLfloat)width/(GLfloat)height, 1.0f ,800.0f);

	glMatrixMode(GL_MODELVIEW);							// Select The Modelview Matrix
	glLoadIdentity();									// Reset The Modelview Matrix
}
//結(jié)束處理
void DeInit()
{
	if (g_hRC)											
	{
		wglMakeCurrent(NULL, NULL);						// This frees our rendering memory and sets everything back to normal
		wglDeleteContext(g_hRC);						// Delete our OpenGL Rendering Context	
	}
	
	if (g_hDC) 
		ReleaseDC(g_hWnd, g_hDC);						// Release our HDC from memory
		
	if(g_bFullScreen)									// If we were in full screen
	{
		ChangeDisplaySettings(NULL,0);					// If So Switch Back To The Desktop
		ShowCursor(TRUE);								// Show Mouse Pointer
	}

	UnregisterClass("GameTutorials", g_hInstance);		// Free the window class

	PostQuitMessage (0);								// Post a QUIT message to the window
}