RE: [Algorithms] visualizing frustum planes?

[Pallister, K. <kim...@in...>]

Also, if you are on DX7 or OpenGL 1.1, you can download the eval version of
GPT from Intel's web site. It include's a 'wide angle' and 'reverse wide
angle' view that will do this transparently for you. Just run the EXE
through it and voila.

Kim Pallister

We will find a way or we will make one.
                     - Hannibal


> -----Original Message-----
> From: Michael S. Harrison [mailto:mic...@ud...]
> Sent: Monday, August 21, 2000 11:31 AM
> To: gda...@li...
> Subject: Re: [Algorithms] visualizing frustum planes?
> 
> 
> Duh.  This is precisely the reason I like working on teams 
> where more than one person is familiar with a given system.  
> Sometimes having someone state the obvious is a good kick in the seat.
> 
> It hadn't even occurred to me to use an artificial model 
> matrix and draw the simulated frustum planes, in order to 
> check (and help visualize) the camera math
> 
> At 07:10 PM 8/21/00, you wrote:
> >Hey,
> >
> >Here's a piece of code which will render the camera frustum, 
> which I find to
> >be useful when hunting camera problems. It works best when 
> viewed from a
> >second camera though (since the frustum is mostly clipped by the very
> >frustum planes it is meant to visualize), with the AABB 
> culling code (or
> >whatever you may end up using it for) hardwired to the first 
> camera - only,
> >the second camera should just render everything, or only 
> rely on culling
> >code of which you're certain that it works.
> >
> >----8<----
> >  float     ax, ay, bx, by, fx, fy;
> >  static Vertex verts[8];
> >  static ushort indices[24] = {
> >   0,1, 1,2, 2,3, 3,0,
> >   4,5, 5,6, 6,7, 7,4,
> >   0,4, 1,5, 2,6, 3,7
> >  };
> >
> >   // Calculate fov/2 angles in x and y direction.
> >  ax = mFov / 2;
> >  ay = ax * ((float) mViewport.height / (float) mViewport.width);
> >   // Calculate x/y coordinates of the front plane.
> >  fx = mFront * (float) tan(ax);
> >  fy = mFront * (float) tan(ay);
> >   // Calculate x/y coordinates of the back plane.
> >  bx = mBack * (float) tan(ax);
> >  by = mBack * (float) tan(ay);
> >   // Setup frustum verts.
> >  verts[0].loc.set(-fx, +fy, mFront);
> >  verts[1].loc.set(+fx, +fy, mFront);
> >  verts[2].loc.set(+fx, -fy, mFront);
> >  verts[3].loc.set(-fx, -fy, mFront);
> >  verts[4].loc.set(-bx, +by, mBack);
> >  verts[5].loc.set(+bx, +by, mBack);
> >  verts[6].loc.set(+bx, -by, mBack);
> >  verts[7].loc.set(-bx, -by, mBack);
> >  for (short i = 0; i < 8; i++)
> >   verts[i].color = Color3(0.8f, 0.8f, 0.8f);
> >   // Render frustum.
> >  GfxDevice->SetTransform(eTransformWorld, mMatrix);
> >  GfxDevice->Draw(GfxDevice::PrimLineList, verts, 8, indices, 24);
> >----8<----
> >
> >If you have any questions about the specifics of the above 
> code, mail me
> >offline.
> >
> >HTH
> >
> >Jim Offerman
> >
> >Innovade
> >- designing the designer
> >----- Original Message -----
> >From: "Michael S. Harrison" <mic...@ud...>
> >To: <gda...@li...>
> >Sent: Monday, August 21, 2000 9:18 AM
> >Subject: [Algorithms] visualizing frustum planes?
> >
> >
> >> I'm attempting to implement the AABB culling code talked 
> about here some
> >time ago and I'm running into a general problem in 
> visualizing the frustum
> >planes used to cull objects based on their AABB's
> >>
> >> I'm using both Klaus Hartmann's AABBCull sample and the 
> Viewcull sample
> >included with the OpenGL FAQ.
> >>
> >> While the code generally works, I'm having some difficulty 
> visualizing the
> >relationship between the plane vector and the "distance" 
> value stored with
> >it, which I'm sure is the reason I can't quite figure out 
> why the code
> >generates intersection results when it should generate a full cull.
> >>
> >> As you might guess, I'm fairly new to the world of 3d 
> projection and I'm
> >still wrapping my mind around all the transformations that 
> take an object
> >from "world" space to screen space.
> >>
> >> Can anyone suggest a reference or way to visualize exactly 
> what's going on
> >with the plane extraction and how the vectors relate back to 
> the AABB?
> >>
> >>
> >> _______________________________________________
> >> GDAlgorithms-list mailing list
> >> GDA...@li...
> >> http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
> >>
> >
> >
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