RE: [Algorithms] Polygon clipping

[Aaron D. <ri...@ho...>]

I might be overlooking something here but I can imagine a case where a fan
would not remain a fan after clipping that might complicate this method.

What happens when the centre of the fan is out of the view frustum? I can't
see how the fan can be preserved. It would be cut into a series of quads
which would no longer share a common vertex. Unless I'm thinking of
something wrongly, these can't be arranged in a fan-like fashion.

- Aaron

> -----Original Message-----
> From: gda...@li...
> [mailto:gda...@li...]On Behalf Of Tom
> Forsyth
> Sent: Wednesday, July 26, 2000 7:50 PM
> To: gda...@li...
> Subject: RE: [Algorithms] Polygon clipping
>
>
>
> Fans remain fans (though it may be knarly to find the ordering), strips
> don't - they can become multiple strips (think about a U-shaped
> strip where
> the bottom of the U is off-screen).
>
> You might also want to try sending objects that intersect the
> frustum edges
> through the non-VB path, so that D3D clips them for you - it's actually
> pretty fast. Things that don't need clipping should still go
> through the VB
> path of course.
>
> Oh, and I really recommend indexed lists instead of lots of little strips
> and fans - you get far too many D3D calls that way, and if you're going to
> do your own clipping, indexed lists are very easy to handle.
>
> Tom Forsyth - Muckyfoot bloke.
> Whizzing and pasting and pooting through the day.
>
> > -----Original Message-----
> > From: Klaus Hartmann [mailto:k_h...@os...]
> > Sent: 25 July 2000 23:49
> > To: gda...@li...
> > Subject: [Algorithms] Polygon clipping
> >
> >
> > Hi all,
> >
> > Even though this is not an API-specific question, I'd like to use an
> > API-specific example to explain my problem.
> >
> > In Direct3D, when using *vertex buffer* with pre-transformed
> > and pre-lit
> > vertices, then Direct3D does not perform any clipping. So I
> > have to do this
> > myself. I could probably go ahead an clip single triangles
> > with a Sutherland
> > Hodgman algorithm, but...
> >
> > How do you people clip triangle strips and triangle fans? Is
> > it possible to
> > clip them so, that strips remain strips, and fans remain
> > fans, or is this
> > impossible?
> >
> > Also, which is the prefered clipping algorithm? Is it
> > Sutherland Hodgman?
> >
> > When you answer, please keep in mind that I also need to clip texture
> > coordinates and the diffuse/specular colors.
> >
> > Any help is greatly appreciated,
> > Niki
> >
> >
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