Re: [Algorithms] Polygon clipping

[Klaus H. <k_h...@os...>]

----- Original Message -----
From: Brian Marshall <bma...@ra...>
To: <gda...@li...>
Sent: Wednesday, July 26, 2000 2:39 PM
Subject: RE: [Algorithms] Polygon clipping


> Different from the normal. I was assuming that the fan was for a convex
> polygon. DOH! For a convex polygon the vertices are in fan order anyway
and
> remain so after clipping. This example is not convex so I guess you could
> use more general polygon clipping.

The point is this... I intend to write a polygon clipper for 2D games using
the 3D hardware (the vertices are already in screen space). Of course, in 2D
games, polygons are usually convex (like particles, or simple textured
blocks), but... In my opinion, polygon clipping is not exactly one of the
most interesting topics, and thus I want to write a clipper that handles all
the standard primitive types (concave, and convex), and never think about it
again. Actually, this is one of those rare cases where I'd say "source code
appreciated" ;-)

> Sutherland-Hodgham will clip concave
> polygons, in this case giving 2 polygons out, or a degenerate triangle
(zero
> area) connecting the 2 fragments. There is some info on this in FvD etc.

Yes, I do have all these standard books, like the Graphics Gems, FvDFH, and
so on... but they are pretty old. Of course, 'old' doesn't make them bad,
but I'd like to know if there are newer/better/faster clipping algorithms
than Sutherland Hodgman and the like, before I start to implement an 'old'
algorithm. Maybe some clipping algorithm that operates in screen space?
(i.e. no need for back-transforms)

Anyway, I'll now move over to a D3D group for my API-specific questions, and
try to ask non-API-specific questions here.

Thanks,
Niki

> If your generating the strips/fans offline it may be worthwhile only
> allowing convex fans - you'd have to time the benefits of bigger fans
> against more complex clipping code.
>
> -Brian.