Help! Angles to Vectors

OpenGL OpenGL: Advanced Coding
1

I’m doing some OpenGl coding and am trying to get a normalized forward, right, and up vector based on the current viewAngles (yaw, pitch, roll ). I’ve seen a function to do this in the Quake source code, but Quake has a convention where Y and Z are swapped in relation to how Y and Z are typically used in OpenGL…and so I’m not sure if I would have to do some conversion on the Quake function so it will work properly. If needed I can provide the Quake function if that would help someone convert it. Thanks so much in advance!

2

As you say, Quake uses a system where z-axis is running from upwards/downwards. And if know how Quake is doind it, just swap all y-coords and z-coords and it should work. Maybe you have to flip one or two axes though. If it doesn’t work, just post the code here.

3

Ok, here’s the code from Quake I, but it doesn’t quite seem to work because the Y and Z axis are swapped in Quake (my math skills aren’t great, so perhaps the solution is easy??):

void AngleVectors( vec3_t ang, vec3_t fwd, vec3_t right, vec3_t up) {
float angle;
float sr, sp, sy, cr, cp, cy;

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

if( fwd ) {
	forward[0] = cp*cy;
	forward[1] = cp*sy;
	forward[2] = -sp;
}
if( right ) {
	right[0] = (-1*sr*sp*cy+-1*cr*-sy);
	right[1] = (-1*sr*sp*sy+-1*cr*cy);
	right[2] = -1*sr*cp;
}
if( up ) {
	up[0] = (cr*sp*cy+-sr*-sy);
	up[1] = (cr*sp*sy+-sr*cy);
	up[2] = cr*cp;
}

}

[This message has been edited by El Jefe (edited 06-08-2000).]

4

Bob, gave your suggestions a whirl last night but it didn’t seem to work. I was able to work out the forward vector, but the right and up vectors are still messed up.

Argh! Someone help, this problem has been holding up my development for a week!

Heh heh, ok, I’ve calmed down now. Seriously, if anyone can help, I’d greatly appreciate it.

Thanks.

5

El Jefe,

Here’s some sample code using my “glh” library - which uses a BSD license and consists only of header files, so use or copy at your discretion.

I’m going to assume that:
yaw is rotation about the y axis
pitch is rotation about the x axis
roll is rotation about the negative z axis

AND the rotations are performed
roll then pitch then yaw

It should be easy to modify this code fragment if those assumptions are incorrect.

rotationf roll(vec3f(0,0,-1), roll_radians);
rotationf pitch(vec3f(1,0,0), pitch_radians);
rotationf yaw(vec3f(0,1,0), yaw_radians);

rotationf composite = yaw;
composite *= pitch;
composite *= roll;

matrix4f m;
composite.get_value(m);

vec3f forward, right, up;
m.mult_matrix_vec(vec3f(0,0,-1), forward);
m.mult_matrix_vec(vec3f(1,0,0), right);
m.mult_matrix_vec(vec3f(0,1,0), up);

Hope this helps…

[This message has been edited by cass (edited 06-09-2000).]

6

Many thanks to anyone who offered tips on how to solve this problem.

I found the Euler Angles rotation matrix at:
http://cadd.cern.ch/cad_geant_int/ddt_long/node11.html

but I had to do some reworking for it to work?? Anyway, if anyone would like the solution I used, I guess let me know?

Thanks again!
El Jefe