# Calculating rotation angel

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I am trying to make my object "point" towards the mouse, however i am having a little bt of trouble to do the calculation. From a previous project i did something like this: but it does not look right.
[source langg = "cpp"]
atan2(mouse_y- object.y, mouse_x- object.x);


object.x/y is the center coordinates for the (square) object. Thanks in adivce! -Mads

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Pickl3d    166
double rotate = (Math.Atan2(mouseY-spriteY,mouseX-spriteX)/Math.PI)*180;//if the sprite is above the mouse point (BASED ON SCREEN CO-ORDINATES, NOT CARTESIAN)if (mouseY>spriteY)  rotate = 360 - rotate; //the heading to faceface_direction(rotate);

First we calculate the angle to rotate using atan2 (important to use ATAN2 not ATAN).

Then we establish if the point is above or below us (if using screen co-ordinates then the y axis value is decreasing as we approach the top of the screen) hence if spriteY<mouseY (above the mouse point), in which case you subtract the result from 360 degrees.

Now the KEY thing to note here is that the sprite is always considered to be facing east (0 degrees), this allows you to get a perfect calculation (it's totally irrelevant that the sprite is facing 0 to start with as he always snaps to the correct mouse facing anyway - so don't get confused by this).

The FACT that you start at 0 and face accordingly either +clockwise or -counterclockwise.

Example result might be 315 degrees, so you rotate from 0, -45degrees to face the mouse.

Bingo! :)

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Hmm still not getting it right.. Im working solely with radians.

[source langg = "cpp"]atan2(mouse_y- object.y, mouse_x- object.x);		if(mouse_y < object.y)       angle = (2*b2_pi) + angle;	 	object.angle = angle ;

hmm its not working..

Clickyyyyyyyy

The red dot would be the mouse pointer.

[Edited by - MadsGustaf on March 3, 2008 1:03:08 PM]

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jyk    2094
If you're using atan2(), you shouldn't have to perform any additional calculations to get the correct angle (aside perhaps from modifying the results for use with a different coordinate system).

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Hmm you seem to be right. Currently i am getting the same result as the image i posted above, but that means i am back at the beginning with

atan2(mouse_y- object.y, mouse_x- object.x);

I do not quite see why it should be that different for another coordinate system. An angle is an angle. I am using SDL's coordinate system where (0,0) is located at top left of the screen and x increase going from left to right, and y increase by going from up to down.

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Zahlman    1682
A vector A - B points from B to A.

Also,

Quote:
 I do not quite see why it should be that different for another coordinate system. An angle is an angle. I am using SDL's coordinate system where (0,0) is located at top left of the screen and x increase going from left to right, and y increase by going from up to down.

Mathematical coordinates have y increasing upward instead of downward. That, in effect, flips the angle vertically: if you pass dy = 10, dx = 0 to the function, you'll get an upward angle (pi / 2 radians), when the desired direction is in fact downwards.

Once you have the angle value, what do you do with it?

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Pickl3d    166
Quote:
 if(mouse_y < object.y) angle = (2*b2_pi) + angle;??You would get angles > 360 here

If this is based on screen co-ordinates, then it's WRONG - I have already shown you how to calculate it properly.

Also I forgot to mention, treat the result as ABSOLUTE eg: rotate = Math.Abs(rotate). This is wise because you can get negative results if the mouse is at 0,0 and the point is "above it.. >0".

angle = atan2(mouse_y-object.y,mouse_x-object.x);	if(mouse_y > object.y) angle = - ABSOLUTE(angle);else angle = ABSOLULTE(angle);rotate_point_to(angle);

Learn to print out the results of the calculations and / or DEBUG and see WHY things are not correct. Atan2 is the correct way to do it.

[Edited by - Pickl3d on March 6, 2008 3:05:02 AM]

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I am still not getting it right.. i have drawn another image to try to explain what is happening.

The object seem to rotate the reverse direction than it is supposed to. For example, if i move the cursor in an arc of 90 degrees, the object will rotate -90 degrres, and will face towards the mouse at 45 degrees. Look at the picture for a clearer view.

The angle in the picture is the angle printed out in degrees. The red dot would be the mouse cursor. The square with the green cross is the object.

Click me!

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Zahlman    1682
Those look to me like exactly the results of not correcting for the two things mentioned in my previous post.

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I understand the part about the y-axis being flipped. But not how you would solve it.. would you multiply dy by -1, to get the inverse? Sorry for being ignorant, but this is really something new to me. I did not quite get the vector part either. How would it have any use in this example?

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jyk    2094
Quote:
 Original post by MadsGustafI understand the part about the y-axis being flipped. But not how you would solve it.. would you multiply dy by -1, to get the inverse? Sorry for being ignorant, but this is really something new to me. I did not quite get the vector part either. How would it have any use in this example?
Zahlman is suggesting that you reverse the terms in the vector subtraction within the call to atan2() (if that's still not clear, post back with your questions and we'll try to clarify things further).

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Hmm. i do not think i am following you, but this was what i tried nevertheless.

double angle = atan2(object.x - mouse_y,mouse_x - object.x );		 	cout << angle*RAD2DEG << endl;	object.rotation = angle;

It does not produce the desired result, so i assume this is not the right approach.

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Pickl3d    166
There is nothing wrong with the atan2 that was shown to you, don't change it.

The problem lies with how you rotate the sprite after the calculation.

HOW do you rotate the sprite with the "object.rotation"?

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I am using OpenGL for drawings. I believe i have inverted the y-axis (using glOrtho to set up projection with origin at top left corner) Atleast with translating and such, y is increasing going from up to down. This is how i draw:

I am iterating over all the objects in the game using the the following functions on them, and the The rotation and all is perfect for all other objects (not using the atan2 function..)

[source langg = "cpp"]Code: //translate to origin glTranslate(object.x,object.y,0); glRotatef(rotation*(180/pi),0,0,1); glBegin(GL_QUADS); //draw the textured quad glEnd(GL_QUADS);

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Pickl3d    166
I can see why it's not working, doh!

glRotatef rotates by the AMOUNT specified not to the HEADING.

Pay close attention here, and I mean pay CLOSE attention... otherwise this saga is going to go on forever :)

----

Now if you recall my VERY FIRST post you will see this statement:

Quote:
 Example result might be 315 degrees, so you rotate from 0, -45degrees to face the mouse.

0 GOING counterclockwise 45 degrees == 315 degrees (the result from atan2), this means that you have tryed to rotate 315 degrees and not -45 !!!!!!!!!!!! BOOM ERROR ERROR! THINK THINK!

Let me show you another few examples:

270 degrees == counterclockwise rotation of 90 degrees(shortest rotation from 0)
10 degrees == clockwise rotation of 10 degrees
170 degrees == clockwise rotation of 170 degrees

You could also use the correct sign from atan2 if you truly know what you are doing, but I think you should brush up on your maths first.

FINALLY, note that glRotatef (assumes a right hand side rule and rotates the OPPOSITE DIRECTION to add even more confusion so invert the rotation to left hand side rule, or at least ensure a clockwise rotation and using - + rotations, - would be counterclock + would be clockwise)

Quote:
 glRotatef(...) NOTES This rotation follows the right-hand rule, so if the vector (x,y,z) points toward the user, the rotation will be counterclockwise.

So in theory (provided you are using screen co-ordinates without transformations and left hand side rotation mode)

double spriteX = 0f;    //spriteXdouble spriteY = 0f;    //spriteYdouble mouseX =  100f;    //mouseXdouble mouseY =  100f;  //mouseYdouble rotate = (Math.Atan2(mouseY-spriteY,mouseX-spriteX) / Math.PI) * 180;rotate = Math.Abs(rotate);if (mouseY > spriteY) rotate = -rotate;

See image for final visual explanation-> http://www.ultanart.co.uk/uberimage.jpg

lol! :)

[Edited by - Pickl3d on March 5, 2008 6:05:40 AM]

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I think i understand what you are saying. atan2() returns the shortest angle to rotate from 0degrees(?). I tried to apply what you described, but i got strange results. The rotation was correct when mouse.y < object.y(even though it was still pi/2 radians off), but as soon as the mouse was moved under the object, it would rotate the reverse direction. I messed a little around with the code, and got it to work, but its not very pretty, as its just me "adding" the remaining angle (pi/2) to the angle.

[source langg = "cpp"]	double angle =  (atan2( event.motion.y - Bluebox.body->GetOriginPosition().y ,event.motion.x - Bluebox.body->GetOriginPosition().x)) ;		angle += (b2_pi/2);	  	cout << angle<< endl;	Bluebox.body->m_rotation = angle ;

I would like to know why it always is 90 degrees/(pi/2) radians off.. Thanks for being really helpful anyway :) i have rated you up.

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Pickl3d    166
Who the heck told you to pi_2/2 and all that nonsense?

Secondly, I showed you how to do it with the latest source in my last post, which is nothing like what you have there - it was changed following the fact you were using glrotatef - read the posts properly please so we don't have to respond 100 times.

Now to finalise this I have actually CODED an OpenGL example for you in C++, just to prove the fact you need to learn to listen :)

Here is the source code:
http://rafb.net/p/nrIDRI42.html

Note: that I just took one of the "NeHe" tutorials and added to the:
Quote:
 int DrawGLScene(GLvoid)

GLfloat rotate = abs((GLfloat)atan2((GLfloat)my-oy,(GLfloat)mx-ox))/PI*180.0f; if (my > oy) rotate = -rotate; glRotatef(rotate,0.0f,0.0f,1.0f);

The result of which is a program with a triangle that follows the mouse like this:

http://www.ultanart.co.uk/Untitled-1.gif

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I am sorry, but the page seem to be down, could you reuploaded please?

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Pickl3d    166
Copy and paste this into a non-unicode c++ project including the appropriate GL lib in the dependencies and run.

#include <windows.h>		// Header File For Windows#include <gl\gl.h>			// Header File For The OpenGL32 Library#include <gl\glu.h>			// Header File For The GLu32 Library#include <gl\glaux.h>		// Header File For The Glaux Library#include <math.h>#define PI       3.14159265358979323846HDC			hDC=NULL;		// Private GDI Device ContextHGLRC		hRC=NULL;		// Permanent Rendering ContextHWND		hWnd=NULL;		// Holds Our Window HandleHINSTANCE	hInstance;		// Holds The Instance Of The Applicationbool	keys[256];			// Array Used For The Keyboard Routinebool	active=TRUE;		// Window Active Flag Set To TRUE By Defaultbool	fullscreen=TRUE;	// Fullscreen Flag Set To Fullscreen Mode By Defaultint mx=0;int my=0;GLfloat	rtri;				// Angle For The Triangle ( NEW )GLfloat	rquad;				// Angle For The Quad ( NEW )LRESULT	CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);	// Declaration For WndProcGLvoid ReSizeGLScene(GLsizei width, GLsizei height)		// Resize And Initialize The GL Window{	if (height==0)										// Prevent A Divide By Zero By	{		height=1;										// Making Height Equal One	}	glViewport(0,0,width,height);						// Reset The Current Viewport	glMatrixMode(GL_PROJECTION);						// Select The Projection Matrix	glLoadIdentity();									// Reset The Projection Matrix	// Calculate The Aspect Ratio Of The Window	gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);	glMatrixMode(GL_MODELVIEW);							// Select The Modelview Matrix	glLoadIdentity();									// Reset The Modelview Matrix}int InitGL(GLvoid)										// All Setup For OpenGL Goes Here{	glShadeModel(GL_SMOOTH);							// Enable Smooth Shading	glClearColor(0.0f, 0.0f, 0.0f, 0.5f);				// Black Background	glClearDepth(1.0f);									// Depth Buffer Setup	glEnable(GL_DEPTH_TEST);							// Enables Depth Testing	glDepthFunc(GL_LEQUAL);								// The Type Of Depth Testing To Do	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);	// Really Nice Perspective Calculations	return TRUE;										// Initialization Went OK}int DrawGLScene(GLvoid)									// Here's Where We Do All The Drawing{	int ox=640/2; //SPRITE POINT X (center of screen for this example)	int oy=480/2; //SPRITE POINT Y (center of screen for this example)	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	// Clear Screen And Depth Buffer	glLoadIdentity();									// Reset The Current Modelview Matrix	glTranslatef(0.0f,0.0f,-10.0f);	      				// Move Left 1.5 Units And Into The Screen 6.0	glRotatef(-90.0f,0.0f,0.0f,1.0f);					//Point the triangle to 0deg	//BY_PICKLED/////////////////////////////////////////////////////////////////	GLfloat rotate = abs((GLfloat)atan2((GLfloat)my-oy,(GLfloat)mx-ox))/PI*180.0f; //ROTATE TO MOUSE	if (my > oy)		rotate = -rotate; 	glRotatef(rotate,0.0f,0.0f,1.0f); 	//BY_PICKLED/////////////////////////////////////////////////////////////////	glBegin(GL_TRIANGLES);								// Start Drawing A Triangle		glColor3f(1.0f,0.0f,0.0f);						// Set Top Point Of Triangle To Red		glVertex3f( 0.0f, 1.0f, 0.0f);					// First Point Of The Triangle		glColor3f(0.0f,1.0f,0.0f);						// Set Left Point Of Triangle To Green		glVertex3f(-1.0f,-1.0f, 0.0f);					// Second Point Of The Triangle		glColor3f(0.0f,1.0f,0.0f);						// Set Right Point Of Triangle To Blue		glVertex3f( 1.0f,-1.0f, 0.0f);					// Third Point Of The Triangle	glEnd();											// Done Drawing The Triangle		rtri+=0.2f;											// Increase The Rotation Variable For The Triangle ( NEW )		return TRUE;										// Keep Going}GLvoid KillGLWindow(GLvoid)								// Properly Kill The Window{	if (fullscreen)										// Are We In Fullscreen Mode?	{		ChangeDisplaySettings(NULL,0);					// If So Switch Back To The Desktop		ShowCursor(TRUE);								// Show Mouse Pointer	}	if (hRC)											// Do We Have A Rendering Context?	{		if (!wglMakeCurrent(NULL,NULL))					// Are We Able To Release The DC And RC Contexts?		{			MessageBox(NULL,"Release Of DC And RC Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);		}		if (!wglDeleteContext(hRC))						// Are We Able To Delete The RC?		{			MessageBox(NULL,"Release Rendering Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);		}		hRC=NULL;										// Set RC To NULL	}	if (hDC && !ReleaseDC(hWnd,hDC))					// Are We Able To Release The DC	{		MessageBox(NULL,"Release Device Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);		hDC=NULL;										// Set DC To NULL	}	if (hWnd && !DestroyWindow(hWnd))					// Are We Able To Destroy The Window?	{		MessageBox(NULL,"Could Not Release hWnd.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);		hWnd=NULL;										// Set hWnd To NULL	}	if (!UnregisterClass("OpenGL",hInstance))			// Are We Able To Unregister Class	{		MessageBox(NULL,"Could Not Unregister Class.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);		hInstance=NULL;									// Set hInstance To NULL	}}/*	This Code Creates Our OpenGL Window.  Parameters Are:					* *	title			- Title To Appear At The Top Of The Window				* *	width			- Width Of The GL Window Or Fullscreen Mode				* *	height			- Height Of The GL Window Or Fullscreen Mode			* *	bits			- Number Of Bits To Use For Color (8/16/24/32)			* *	fullscreenflag	- Use Fullscreen Mode (TRUE) Or Windowed Mode (FALSE)	*/ BOOL CreateGLWindow(char* title, int width, int height, int bits, bool fullscreenflag){	GLuint		PixelFormat;			// Holds The Results After Searching For A Match	WNDCLASS	wc;						// Windows Class Structure	DWORD		dwExStyle;				// Window Extended Style	DWORD		dwStyle;				// Window Style	RECT		WindowRect;				// Grabs Rectangle Upper Left / Lower Right Values	WindowRect.left=(long)0;			// Set Left Value To 0	WindowRect.right=(long)width;		// Set Right Value To Requested Width	WindowRect.top=(long)0;				// Set Top Value To 0	WindowRect.bottom=(long)height;		// Set Bottom Value To Requested Height	fullscreen=fullscreenflag;			// Set The Global Fullscreen Flag	hInstance			= GetModuleHandle(NULL);				// Grab An Instance For Our Window	wc.style			= CS_HREDRAW | CS_VREDRAW | CS_OWNDC;	// Redraw On Size, And Own DC For Window.	wc.lpfnWndProc		= (WNDPROC) WndProc;					// WndProc Handles Messages	wc.cbClsExtra		= 0;									// No Extra Window Data	wc.cbWndExtra		= 0;									// No Extra Window Data	wc.hInstance		= hInstance;							// Set The Instance	wc.hIcon			= LoadIcon(NULL, IDI_WINLOGO);			// Load The Default Icon	wc.hCursor			= LoadCursor(NULL, IDC_ARROW);			// Load The Arrow Pointer	wc.hbrBackground	= NULL;									// No Background Required For GL	wc.lpszMenuName		= NULL;									// We Don't Want A Menu	wc.lpszClassName	= "OpenGL";								// Set The Class Name	if (!RegisterClass(&wc))									// Attempt To Register The Window Class	{		MessageBox(NULL,"Failed To Register The Window Class.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;											// Return FALSE	}		if (fullscreen)												// Attempt Fullscreen Mode?	{		DEVMODE dmScreenSettings;								// Device Mode		memset(&dmScreenSettings,0,sizeof(dmScreenSettings));	// Makes Sure Memory's Cleared		dmScreenSettings.dmSize=sizeof(dmScreenSettings);		// Size Of The Devmode Structure		dmScreenSettings.dmPelsWidth	= width;				// Selected Screen Width		dmScreenSettings.dmPelsHeight	= height;				// Selected Screen Height		dmScreenSettings.dmBitsPerPel	= bits;					// Selected Bits Per Pixel		dmScreenSettings.dmFields=DM_BITSPERPEL|DM_PELSWIDTH|DM_PELSHEIGHT;		// Try To Set Selected Mode And Get Results.  NOTE: CDS_FULLSCREEN Gets Rid Of Start Bar.		if (ChangeDisplaySettings(&dmScreenSettings,CDS_FULLSCREEN)!=DISP_CHANGE_SUCCESSFUL)		{			// If The Mode Fails, Offer Two Options.  Quit Or Use Windowed Mode.			if (MessageBox(NULL,"The Requested Fullscreen Mode Is Not Supported By\nYour Video Card. Use Windowed Mode Instead?","NeHe GL",MB_YESNO|MB_ICONEXCLAMATION)==IDYES)			{				fullscreen=FALSE;		// Windowed Mode Selected.  Fullscreen = FALSE			}			else			{				// Pop Up A Message Box Letting User Know The Program Is Closing.				MessageBox(NULL,"Program Will Now Close.","ERROR",MB_OK|MB_ICONSTOP);				return FALSE;									// Return FALSE			}		}	}	if (fullscreen)												// Are We Still In Fullscreen Mode?	{		dwExStyle=WS_EX_APPWINDOW;								// Window Extended Style		dwStyle=WS_POPUP;										// Windows Style		//ShowCursor(FALSE);										// Hide Mouse Pointer	}	else	{		dwExStyle=WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;			// Window Extended Style		dwStyle=WS_OVERLAPPEDWINDOW;							// Windows Style	}	AdjustWindowRectEx(&WindowRect, dwStyle, FALSE, dwExStyle);		// Adjust Window To True Requested Size	// Create The Window	if (!(hWnd=CreateWindowEx(	dwExStyle,							// Extended Style For The Window								"OpenGL",							// Class Name								title,								// Window Title								dwStyle |							// Defined Window Style								WS_CLIPSIBLINGS |					// Required Window Style								WS_CLIPCHILDREN,					// Required Window Style								0, 0,								// Window Position								WindowRect.right-WindowRect.left,	// Calculate Window Width								WindowRect.bottom-WindowRect.top,	// Calculate Window Height								NULL,								// No Parent Window								NULL,								// No Menu								hInstance,							// Instance								NULL)))								// Dont Pass Anything To WM_CREATE	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Window Creation Error.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	static	PIXELFORMATDESCRIPTOR pfd=				// pfd Tells Windows How We Want Things To Be	{		sizeof(PIXELFORMATDESCRIPTOR),				// Size Of This Pixel Format Descriptor		1,											// Version Number		PFD_DRAW_TO_WINDOW |						// Format Must Support Window		PFD_SUPPORT_OPENGL |						// Format Must Support OpenGL		PFD_DOUBLEBUFFER,							// Must Support Double Buffering		PFD_TYPE_RGBA,								// Request An RGBA Format		bits,										// Select Our Color Depth		0, 0, 0, 0, 0, 0,							// Color Bits Ignored		0,											// No Alpha Buffer		0,											// Shift Bit Ignored		0,											// No Accumulation Buffer		0, 0, 0, 0,									// Accumulation Bits Ignored		16,											// 16Bit Z-Buffer (Depth Buffer)  		0,											// No Stencil Buffer		0,											// No Auxiliary Buffer		PFD_MAIN_PLANE,								// Main Drawing Layer		0,											// Reserved		0, 0, 0										// Layer Masks Ignored	};		if (!(hDC=GetDC(hWnd)))							// Did We Get A Device Context?	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Can't Create A GL Device Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	if (!(PixelFormat=ChoosePixelFormat(hDC,&pfd)))	// Did Windows Find A Matching Pixel Format?	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Can't Find A Suitable PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	if(!SetPixelFormat(hDC,PixelFormat,&pfd))		// Are We Able To Set The Pixel Format?	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Can't Set The PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	if (!(hRC=wglCreateContext(hDC)))				// Are We Able To Get A Rendering Context?	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Can't Create A GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	if(!wglMakeCurrent(hDC,hRC))					// Try To Activate The Rendering Context	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Can't Activate The GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	ShowWindow(hWnd,SW_SHOW);						// Show The Window	SetForegroundWindow(hWnd);						// Slightly Higher Priority	SetFocus(hWnd);									// Sets Keyboard Focus To The Window	ReSizeGLScene(width, height);					// Set Up Our Perspective GL Screen	if (!InitGL())									// Initialize Our Newly Created GL Window	{		KillGLWindow();								// Reset The Display		MessageBox(NULL,"Initialization Failed.","ERROR",MB_OK|MB_ICONEXCLAMATION);		return FALSE;								// Return FALSE	}	return TRUE;									// Success}LRESULT CALLBACK WndProc(	HWND	hWnd,			// Handle For This Window							UINT	uMsg,			// Message For This Window							WPARAM	wParam,			// Additional Message Information							LPARAM	lParam)			// Additional Message Information{	switch (uMsg)									// Check For Windows Messages	{		case WM_ACTIVATE:							// Watch For Window Activate Message		{			if (!HIWORD(wParam))					// Check Minimization State			{				active=TRUE;						// Program Is Active			}			else			{				active=FALSE;						// Program Is No Longer Active			}			return 0;								// Return To The Message Loop		}				case WM_MOUSEMOVE:		{			mx = LOWORD(lParam);			my = HIWORD(lParam);		}		case WM_SYSCOMMAND:							// Intercept System Commands		{			switch (wParam)							// Check System Calls			{				case SC_SCREENSAVE:					// Screensaver Trying To Start?				case SC_MONITORPOWER:				// Monitor Trying To Enter Powersave?				return 0;							// Prevent From Happening			}			break;									// Exit		}		case WM_CLOSE:								// Did We Receive A Close Message?		{			PostQuitMessage(0);						// Send A Quit Message			return 0;								// Jump Back		}		case WM_KEYDOWN:							// Is A Key Being Held Down?		{			keys[wParam] = TRUE;					// If So, Mark It As TRUE			return 0;								// Jump Back		}		case WM_KEYUP:								// Has A Key Been Released?		{			keys[wParam] = FALSE;					// If So, Mark It As FALSE			return 0;								// Jump Back		}		case WM_SIZE:								// Resize The OpenGL Window		{			ReSizeGLScene(LOWORD(lParam),HIWORD(lParam));  // LoWord=Width, HiWord=Height			return 0;								// Jump Back		}	}	// Pass All Unhandled Messages To DefWindowProc	return DefWindowProc(hWnd,uMsg,wParam,lParam);}int WINAPI WinMain(	HINSTANCE	hInstance,			// Instance					HINSTANCE	hPrevInstance,		// Previous Instance					LPSTR		lpCmdLine,			// Command Line Parameters					int			nCmdShow)			// Window Show State{	MSG		msg;									// Windows Message Structure	BOOL	done=FALSE;								// Bool Variable To Exit Loop	// Ask The User Which Screen Mode They Prefer	//if (MessageBox(NULL,"Would You Like To Run In Fullscreen Mode?", "Start FullScreen?",MB_YESNO|MB_ICONQUESTION)==IDNO)	//{		fullscreen=FALSE;							// Windowed Mode	//}	// Create Our OpenGL Window	if (!CreateGLWindow("NeHe's Rotation Tutorial",640,480,16,fullscreen))	{		return 0;									// Quit If Window Was Not Created	}	while(!done)									// Loop That Runs While done=FALSE	{		if (PeekMessage(&msg,NULL,0,0,PM_REMOVE))	// Is There A Message Waiting?		{			if (msg.message==WM_QUIT)				// Have We Received A Quit Message?			{				done=TRUE;							// If So done=TRUE			}			else									// If Not, Deal With Window Messages			{				TranslateMessage(&msg);				// Translate The Message				DispatchMessage(&msg);				// Dispatch The Message			}		}		else										// If There Are No Messages		{			// Draw The Scene.  Watch For ESC Key And Quit Messages From DrawGLScene()			if ((active && !DrawGLScene()) || keys[VK_ESCAPE])	// Active?  Was There A Quit Received?			{				done=TRUE;							// ESC or DrawGLScene Signalled A Quit			}			else									// Not Time To Quit, Update Screen			{				SwapBuffers(hDC);					// Swap Buffers (Double Buffering)			}			if (keys[VK_F1])						// Is F1 Being Pressed?			{				keys[VK_F1]=FALSE;					// If So Make Key FALSE				KillGLWindow();						// Kill Our Current Window				fullscreen=!fullscreen;				// Toggle Fullscreen / Windowed Mode				// Recreate Our OpenGL Window				if (!CreateGLWindow("NeHe's Rotation Tutorial",640,480,16,fullscreen))				{					return 0;						// Quit If Window Was Not Created				}			}		}	}	// Shutdown	KillGLWindow();									// Kill The Window	return (msg.wParam);							// Exit The Program}