[gameprogrammer] Re: flight simulation camera

Hi Richard,

When I turrn the plane around the Y axe in global coordinates the plane turns 
on his Y axe in the same time. Now with your function the camera turns around Y 
with the plane in the plane coordinates.
I have just a little problem because the camera looks always straight (the 
camera doesn't turn on her Y axe) but I think it's not a big problem.

thanks for your help,

Julien
Date: Fri, 28 Sep 2007 09:59:33 +0100
From: richard.sabbarton@xxxxxxxxx
To: julienbreton@xxxxxxxxxx; gameprogrammer@xxxxxxxxxxxxx
Subject: [gameprogrammer] Re: flight simulation camera

Hi Julien,
 
It is assumed that you already know your rotation.  This, in your case would be 
the position/rotation of the plane.  So, assume your Plane is at plX,plY,plZ 
and is rotated by prX, prY, prZ.
 
Your camera position would be behind the plane so plX, plY - CameraDistance, 
plZ.  You would have an offset camera position of 0,CameraDistance,0.
 
So of you had a point class with the RotatePoint() function you could use...
 
CMyPoint CameraOffset;
 
CameraOffset.x = 0;
CameraOffset.y = -5; (distance of camera)
CameraOffset.z = 0;
 
CameraOffset.RotatePoint(prX,prY,prZ);
 
This would take your camera offset and rotate it around Zero...  You can then 
move your camera to that point which would be
 
CameraOffset.xRotated + plX , CameraOffset.yRotated + plY , 
CameraOffset.zRotated + plZ
 
This is the actual position of the camera to place it behind the plan.  You 
then need to rotate the camera at the same angle as your plane using whatever 
code you are using now.
 
Regards
 
Richard
 
On 28/09/2007, Julien Breton <julienbreton@xxxxxxxxxx> wrote:


Hello,

Thanks for your code,

I have a question,
When you have calculate xRotated, yRotated and zRotate give you the values to 
glRotatef function ? (ex : glRotatef (xRotated, 1.0, 0.0, 0.0)), may be I can 
use gluLookAt?


Thanks,

 Julien.



Date: Thu, 27 Sep 2007 11:07:06 +0100
From: richard.sabbarton@xxxxxxxxx 

To: gameprogrammer@xxxxxxxxxxxxx
Subject: [gameprogrammer] Re: flight simulation camera



Hi There,
 
I had exactly the same problem recently because I was making some calculations 
in the wrong order.  The problem was with the glTranslate and glRotate.  I tend 
to rotate the world around the camera rather than the camera around the world.  
So I will first do a glTranslate/rotate to move to the point you want to draw 
your plane.  Then do a glPushMatrix() and render the rest of your scene.  Once 
the rest of your scene is drawn then you can do glPopMatrix() and then render 
the plane.  It should always be right where you want it to be. 

 
I am just a beginner really.  But this is how I would do this.  There are 
probably better ways.
 
The problem I ran into was the start point of ammo when firing.  I wanted my 
bullets to appear to fire from underneath you but, when looking down, they 
started right in front of you.  And when looking up you couldn't see them all.  
Sounds like a similar issue.  The problem is that you know the angle of your 
plane and you know the distance behind it that you want to move but what you 
need calculate is the x,y,z of the camera.  In the same way I needed to 
calculate the x,y,z of my ammo start point.  I wrote the following code to 
rotate a 3D point as part of a 3D point class I was working on. 

 
 // x,y,z are members of a 3D Point Class as are xRotated
// yRotated and zRotated.  We use the rotated points for 
// rendering but we leave the original x,y,z unchanged
// to avoid any distortion.

RotatePoint(int DegAroundX, int DegAroundY, int DegAroundZ){

        // Define some variables needed to perform the rotation
        FLOAT oldx,oldy,oldz,newx,newy,newz,alpha;      // We need to use FLOAT 
values for accuracy

        oldx = x;
        oldy = y;
        oldz = z;

        // ROTATE AROUND Y FIRST;
        alpha = (FLOAT)DegAroundY / (FLOAT)57.29578;    // We have to divide 
Degrees by 57.29578
                                                        // to convert to radians
        newx = cos(alpha)*oldx - sin(alpha)*oldz;
        newy = oldy;
        newz = sin(alpha)*oldx + cos(alpha)*oldz;
        
        oldx = newx;    // After each rotation we have to ensure
        oldy = newy;    // that the new values are pushed into the
        oldz = newz;    // old values because otherwise we will be
                        // rotating partially rotated values.

        // Then Around X;
        alpha = (FLOAT)DegAroundX / (FLOAT)57.29578;    
        newz = cos(alpha)*oldz - sin(alpha)*oldy;
        newy = sin(alpha)*oldz + cos(alpha)*oldy;
        newx = oldx;
        
        oldx = newx;
        oldy = newy;
        oldz = newz;

        // Then Around Z;
        alpha = (FLOAT)DegAroundZ / (FLOAT)57.29578;    
        newx = cos(alpha)*oldx - sin(alpha)*oldy;
        newy = sin(alpha)*oldx + cos(alpha)*oldy;
        newz = oldz;

        xRotated = newx;
        yRotated = newy;
        zRotated = newz;

}
I apologise for the minimal comments.  cos, sin & tan were giving me a headache 
by the time I was done.  I started putting a repository of notes and stuff on 
my website.  You can take a look at it here. 
http://www.fullonsoftware.co.uk/main.html.  I put them in my Snippets section.  
Lots of my beginners stuff about openGL and C++.  Plus some screenshots of my 
(now stalled) most recent project.
 
Regards
 
Richard

 
On 27/09/2007, Julien Breton <julienbreton@xxxxxxxxxx> wrote: 

Thanks for your answer,

My probleme is that my camera don't stay locked to the plane. When I start my 
exe the camera is behind the plane but when I turn the plane around the Y axe 
(in global coordinates) the camera moves but don't stay behind the plane. I can 
always see the plane but on the right (or left) and front at the end but I want 
stay behind the plane. 

It's not easy to explain and sorry for my English.
I use C++/OpenGL

Julien

> From: david@xxxxxxxxxxx 

> To: gameprogrammer@xxxxxxxxxxxxx
> Subject: [gameprogrammer] Re: flight simulation camera 

> Date: Thu, 27 Sep 2007 09:40:31 +0200 

> 
> On Thursday 27 September 2007, Julien Breton wrote:
> > 
> > Hello,
> > 
> > Do you know where I can find an example of a flight simulation 
> > camera ?

> 
> What do you mean, exactly?
> 
> From what I've seen, the basic logic of how the camera works in 
> simulators (flight, racing etc) is that it's simply locked to the 
> vehicle, ie it sits where the pilot/driver would be, looking straight 

> ahead.
> 
> In racing simulators, it's common to add minor adjustments to the 
> position and view angle of the camera, to hint about the G-forces 
> that are "lost in transmission". (Lost, unless you're using a moving 

> platform, that is.) I suppose you could do that in a flight simulator 
> too, but I can't remember seeing that. X-Plane has a different 
> solution: Blackout and redout is simulated by fading the view to 

> black and red respectively. Simple and effective. (Not very not 
> relevant to racing though, as you'd normally never get that kind of 
> G-forces on the vertical axis in a car for extended periods of time.)

> 
> 
> //David Olofson - Programmer, Composer, Open Source Advocate
> 
> .------- http://olofson.net
 - Games, SDL examples -------.
> | http://zeespace.net - 2.5D rendering engine |
> | 
http://audiality.org - Music/audio engine |
> | http://eel.olofson.net - Real time scripting |
> '-- 
http://www.reologica.se - Rheology instrumentation --' 
> 
> ---------------------
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> 
> 



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