RE: [Algorithms] Polygon clipping

[Brian M. <bma...@ra...>]

A triangle fan will remain a triangle fan after clipping to a convex clip
boundary. So if you're clipping to a normal 6 plane view frustrum the fan
stays a fan, though it may have more or less vertices afterwards.

As to triangle strips check out:

	'Three Dimensional Homogenous Clipping of Triangle Strips' Patrick-Gilles
Maillot, Graphics Gems II

If you don't have the book the code is on the net.

When you clip a strip you can get zero or more strips out, or output at most
one strip with degenerate triangles. (The degenerate triangles are used for
jumping along a clip boundary when a hole section of the strip is outside
the clip volume.)

The strip clipping code uses the clip against one plane at a time approach
of Sutherland-Hodgman, but exploits the strip structure to improve
performance.

As to the choice of clipping algorithm - I think that belongs more on a D3D
list for your example, but it may well be worth seeing how quick D3D is at
doing the clipping itself.

-Brian.

> -----Original Message-----
> From: gda...@li...
> [mailto:gda...@li...]On Behalf Of Klaus
> Hartmann
> Sent: Tuesday, July 25, 2000 11:49 PM
> 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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