# AngleVector?

Hello…
I’ve got a bit of a problem/question regarding directional vectors…

After messing around with Quake’s AngleVectors() function (which creates a directional vector from YAW,PITCH & ROLL)…well here it is (Quake’s) to begin with:

``````
float       angle;
float       sr, sp, sy, cr, cp, cy;

angle = angles[YAW] * (M_PI*2 / 360);
sy = sin(angle);
cy = cos(angle);
angle = angles[PITCH] * (M_PI*2 / 360);
sp = sin(angle);
cp = cos(angle);
angle = angles[ROLL] * (M_PI*2 / 360);
sr = sin(angle);
cr = cos(angle);

forward[0] = cp*cy;
forward[1] = cp*sy;
forward[2] = -sp;

``````

As I was saying, after modifying the code so that it can work with OpenGL’s world coordination (i.e. Y-axis being up, instead of Quake’s Z-up axis)…I ended up with:

``````
float sr,sp,sy,cr,cp,cy;

vec[0] = cp*sy;
vec[2] = cp*cy;
vec[1] = -sp;

~~~~~~~~~~~~~~~~~~~

My question is....HOW DOES IT WORK?????
I know how to do ray projection, clipping, plane work....but I can't understand this relatively simple code....

I would have thought that you would have done Matrix rotation...but when i did that..it would mess up my forward direction when aiming up a bit (it would go right a bit)....and im sure that my matrix code is correct.....

Sorry to post all the code and this message, but I really need to figure this little thing out.....

If anyone can explain why you do the cos(angle)*sin(angle), etc calculations, or any explanations, I would GREATLY appreciate it,

Thanks  [img]http://www.opengl.org/discussion_boards/ubb/smile.gif[/img]``````

Okay…it seems as though I fixed the problem by mistake

You are supposed to do a PITCH before a YAW (not the other way around)…

But STILL, how does Quake do it like this??

I was messing around with putting three rotations (around the x y and z axis respectivly) in one matrix. So I had an angle for y-rotation (what you call YAW right?) and one for X rotation (PITCH?) and one for Z rotation (ROLL?). Then I just put these values in the matrix I ended up with (the one compining all three rotations in one). Then I multiplied a vector pointing down the negative Z-axis (0,0,-1) by this matrix to get the new direction vector.
And well, it worked. And I seem to remember it looked something like the code you have up there. Basically a lot of stuff is multiplied by zero so there’s no need putting that in there. So what you see above is probably what’s left of the XYZ-rotation-matrix after you multiply (0,0,-1) with it.

I don’t have my code in front of me so I’m not sure, but I believe it looked something like that.

Hmm… Now that I think about it, I didn’t get it to work fully! =)
The only rotation that worked satisfactory was that around the Y-axis. So I assume you should multiply the rotation-matrixes in ZYX (Y is in the same order, but the other two axises are switched) order and not XYZ order. You would end up with a completly different rotation matrix. I’m sure THAT’s how they do it! =)

Yeah, I did exactly the same thing…the wrong order thing…here is my WORKING
code:

``````
SetIdentityAngle(vec);  // (0,0,-1)
SetIdentityMatrix(matx);
SetIdentityMatrix(maty);
SetIdentityMatrix(matz);

MatrixRotate(maty,angle[YAW],YAW);
MatrixRotate(matx,angle[PITCH],PITCH);
MatrixRotate(matz,-angle[ROLL],ROLL); // Negative because Z is going into screen

VectorByMatrix(vec,matx);
VectorByMatrix(vec,maty);
VectorByMatrix(vec,matz);

``````

This works fine now…

It confuses the hell out of you when you do do the rotations the wrong way around…like they actual WORK, but just not quite so…

I think the quake thing, is yes…putting eular’s angles STRAIGHT into the matrix-multiplicator…without the unnecessary bits…I think…

Thanks anyway