RE: [Algorithms] Polygon clipping

[Tom F. <to...@mu...>]

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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