 # Movement with OpenGL?

Hi!
I have a problem:
To run arround in my Q3-Viewer I do the following calc if the up-key was pressed to move forward in the world:

xpos-= sin(yrotpiover180) * speed;
zpos-= cos(yrot
piover180) * speed;

//yrot is the value I passed into OpenGl
//this way: glRotatef(yrot,0,1,0)

It works perfectly. However if I want to strafe left\right I have to swap sin and cos(at least I calculated this with pencil&paper) but this doesn´t work.

Why?

P.s.:Perhaps I did something wrong ´cause I cannot find a precise definition of the angle
-part of glrotatef(…);

A quick thought…

from what I gather, you’ve split the vector of your motion into:

xpos-= sin(yrotpiover180) * speed;
zpos-= cos(yrot
piover180) * speed;

(I might be wrong here, I’m just scribbling on some paper)

to strafe right try using:

xpos+= sin(yrotpiover180) * speed;
zpos-= cos(yrot
piover180) * speed;

And left:

xpos-= sin(yrotpiover180) * speed;
zpos+= cos(yrot
piover180) * speed;

Thats what my paper reckons…Hope it works I think you must also swap the sin-cos :
to strafe right try using:
xpos+= cos(yrotpiover180) * speed;
zpos-= sin(yrot
piover180) * speed;

update:
And perhaps you must clean your code.
If your code works, then you probably using something like that :
glRotate(360-yrot,0,1,0);
I found that because in my code I use glRotate(yrotation,0,1,0); and I walk with :
void walk(float a)
{
}
//speed=a*dt

[This message has been edited by pavlos (edited 09-20-2000).]

Hi!
Thanx guys, I´ll again ask my paper to check where I made the fault and try your ideas.

P.s.:I use glRotate(360-yrot,0,1,0) which is the same as glRotate(-yrot,0,1,0).

Greets, XBTC!

I looked at the problem and your solutions are both right:One needs to swap cos\sin and negate one of them to strafe.I just ignored the signs in my drawing.

Greets, XBTC!

[This message has been edited by XBCT (edited 09-23-2000).]

I walk through a maze in one of my programs and this is what I use to do the strafe:
case ‘0’: //sidestep left
incrementX = sin(Theta*(pi/180)-pi/2) * 0.2;
incrementY = cos(Theta*(pi/180)-pi/2) * 0.2;
tempX = transX - (2incrementX) + int((gridsize-1)/2);
tempY = transY - (2
incrementY) + int((gridsize-1)/2);
if (maze.showcolor(int((gridsize-1) - tempX),int((gridsize-1) - tempY))>0)
{
transX = transX - incrementX;
transY = transY - incrementY;
}
break;
case ‘.’: //sidestep right
incrementX = sin(Theta*(pi/180)-pi/2) * 0.2;
incrementY = cos(Theta*(pi/180)-pi/2) * 0.2;
tempX = transX + (2incrementX) + int((gridsize-1)/2);
tempY = transY + (2
incrementY) + int((gridsize-1)/2);
if (maze.showcolor(int((gridsize-1) - tempX),int((gridsize-1) - tempY))>0)
{
transX = transX + incrementX;
transY = transY + incrementY;
}
break;
and it works. I know it’s been resolved but it is helpful to see it again sometimes.

If it makes it easier to under stand, you could simply add 90 degrees and subtract 90 degrees and use the same equation. It adds a little to the computation, but if its easier/faster to get something done versus sitting down a calculating, then you could optimize later.

Thanx guys but hey as I already said it works now, I just dropped a sign in my calculations on paper.

Greets, XBTC!