[gameprogrammer] Re: Rotation, Rotation, Rotation...

  • From: Vince <uberneen@xxxxxxxxx>
  • To: gameprogrammer@xxxxxxxxxxxxx
  • Date: Tue, 18 Mar 2008 12:59:35 -0700 (PDT)

Your method sounds plausible to me, and it immediately
makes more sense than trying to figure out what is
actually going on with quaternion math.

I may toy around with it in my test framework as I get
time.  Good luck!

Vince~

--- richard sabbarton <richard.sabbarton@xxxxxxxxx>
wrote:

> Hi Vince,
> 
> This is exactly the issue.  I want x and y movement
> of the mouse to
> control rotation in free 360 deg on all axis. 
> Gimbal Lock is an issue
> and following some additional reading I think I can
> do it.  Also, I
> think I can stop short of using Quarternians to do
> it.
> 
> My plan is this...
> 
> Define my camera orientation as two vectors,
> Direction (vD) and Up
> (vU), with a 3rd vector at 0,0,0 (vO) for the
> origin.  I can then use
> gluLookAt to set the camera.
> 
> With these 3 vectors I can rotate my camera in any
> way without
> suffering from gimbal lock.
> 
> For Left/Right rotation I can rotate vD around the
> axis defined by vU.
>  Roll rotation I can rotate vU around the axis
> defined by vD.  For
> up/down rotation I will rotate vD around the Cross
> Product of the
> vectors vU vD.
> 
> I haven't done this yet but I think it works in
> theory.  What I need
> to do is put together an efficient routing to rotate
> a vector around
> an arbitrary axis.  The glRotatef() function does
> eactly this but my
> problem is that I am going to need the vectors so I
> think I will need
> to code this myself.
> 
> Richard
> 
> 
> On 18/03/2008, Vince <uberneen@xxxxxxxxx> wrote:
> > --- richard sabbarton
> <richard.sabbarton@xxxxxxxxx>
> > wrote:
> >
> > > Hi Robbert,
> > >
> > > I have been looking into this a bit further and
> I
> > > think I can describe
> > > the problem a little better. (maybe)...
> > >
> > > OK.  What I want is to be able to rotate my
> Player
> > > view around my
> > > players axis and not the global axis.  So, if my
> > > player starts out, as
> > > is default, looking down the Z Axis and then
> looks
> > > down I want my
> > > players Z axis to point down so that a rotation
> > > around my players axis
> > > are relative to the player and not the global
> axis.
> > >
> > > Lets say my control keys are up,down,left and
> right.
> > >  If my player
> > > pushes down by 90 deg and then pushes left by 90
> deg
> > > I want my player
> > > to now be on its side looking 90 deg to the left
> of
> > > its original
> > > position.
> > >
> > > Currently, pushing down for 90 deg looks down
> but
> > > then the left action
> > > rotates the view and I am still looking down.
> > >
> > > I read the Quaternion Camera tutorial that Vince
> > > sent through (Thanks
> > > Vince) but I don't think I really understood it.
>  It
> > > has
> > > copy/paste'able code that I think would do
> exactly
> > > what I want but I
> > > would prefer to do something I understand. 
> Also, I
> > > will need the same
> > > functionality for objects in my world as well
> and I
> > > am not sure, given
> > > the calculations involved, that this is going to
> run
> > > quick enough.
> > >
> > > I have been looking into rotation matrices and
> > > transforms as well.
> > >
> > > One thing has certainly become clear... My Math
> is
> > > letting me down.  I
> > > have a feeling the answer to my problem lies in
> a
> > > trip to the bookshop
> > > for some Math Texts and a large supply of sugary
> > > snacks and caffeine
> > > based drinks.
> > >
> > > The thing is, there are tons of tutorials out
> there
> > > that explain how
> > > to do this.  The problem is that they all seem
> to
> > > assume a certain
> > > ammount of knowledge on the subject before they
> > > begin.  Again, back to
> > > the Math Texts...
> > >
> > > Richard
> >
> >
> > This is the FPS camera that I've implemented in my
> > testing framework.
> >
> > I track xpos, ypos, zpos, xrot, yrot, and zrot.
> > I also have storage for lastx and lasty, but that
> > applies to mouse movement so it's not absolutely
> > necessary.
> >
> > This is just my sloppy testing framework, so I
> don't
> > do things like compute for timescale.  You might
> > normally replace the multiplication by 0.5 to a
> value
> > determined by your frame loop.
> >
> > When you press
> > 'Forward'
> >
> > yrotrad = (yrot / 180 * PI);
> > xrotrad = (xrot / 180 * PI);
> > xpos += (float) sin(yrotrad) * 0.5;
> > zpos -= (float) cos(yrotrad) * 0.5;
> > ypos -= (float) sin(xrotrad) * 0.5;
> >
> > 'Backward'
> >
> > yrotrad = (yrot / 180 * PI);
> > xrotrad = (xrot / 180 * PI);
> > xpos -= (float) sin(yrotrad) * 0.5;
> > zpos += (float) cos(yrotrad) * 0.5;
> > ypos += (float) sin(xrotrad) * 0.5;
> >
> > 'Left'
> >
> > yrotrad = (yrot / 180 * PI);
> > xpos += (float) cos(yrotrad) * 0.5;
> > zpos += (float) sin(yrotrad) * 0.5;
> >
> > 'Right'
> >
> > yrotrad = (yrot / 180 * PI);
> > xpos -= (float) cos(yrotrad) * 0.5;
> > zpos -= (float) sin(yrotrad) * 0.5;
> >
> > I handle rotation through the mouse, but this
> could be
> > handled any way that you want.
> > My function takes x and y, which represent the
> current
> > mouse position.  Since I'm using GLFW, it's not
> > constrained to the screen size.
> >
> > diffx=x-lastx;
> > diffy=y-lasty;
> > lastx=x;
> > lasty=y;
> > xrot += (float) diffy * 0.2;
> > yrot += (float) diffx * 0.2;
> >
> > if(xrot > 360) { xrot -= 360; }
> > if(xrot < 0) { xrot += 360; }
> >
> > if(yrot > 360) { yrot -= 360; }
> > if(yrot < 0) { yrot += 360; }
> >
> > When I draw, I first translate to the player
> position
> > using a camera() function.
> >
> > glRotatef(xrot,1.0,0.0,0.0);
> > glRotatef(yrot,0.0,1.0,0.0);
> > glTranslated(-xpos,-ypos,-zpos);
> 
=== message truncated ===



      
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