Eliminating discontinuities (T-junctions) in BSP?

trzy · 2004-06-09T13:49:13

Hi, I''ve asked about this topic here in the past but I''ve never found a sufficient answer and I''ve been sidetracked for the last year or 2 with other unrelated projects. To get to the point: When building a BSP world out of an arbitrary set of polygons (3, 4, or even more vertices), discontinuities result between some of the edges of my software renderer. These are due to T-junctions that are inevitably formed during the polygon splitting process. Is there an easy way of dealing with this? Triangulation won''t solve the problem. Inserting extra vertices at the junctions will fix the problem but determining when this should be done is time consuming. How would a BSP tool (such as id''s tools for Quake 2 and 3 maps) ensure that the resulting polygons for a BSP map do not create discontinuities when rendered? One simple solution I''ve thought of is to arrange the input geometry such that each edge of a polygon only touches at most one other edge (ensuring T-junctions in coplanar polygons cannot occur) and that edges of polygons never touch another polygon without sharing vertices. Perhaps 3D modelling and mapping tools can export such geometry but for arbitrary lists of polygons, these conditions cannot be guaranteed. Do BSP packages simply ignore the issue of discontinuities and assume the input geometry is structured such that they won''t occur no matter what kind of splitting occurs? ---- Bart

Graphics and GPU Programming Programming

Started by trzy June 08, 2004 01:02 AM

9 comments, last by trzy 19 years, 10 months ago

Karg

133

June 09, 2004 01:36 PM

quote:Original post by Yann L
This is the approach I took, and it isn't really that time consuming.

That's essentially the same approach as the half-edge structure. It takes me about 5 sec to create and traverse the half-edge structure from a ply file with about 2.6mil tris. The H-E structure also works with arbitrary sided polygons, though splitting them into triangles isn't hard (I split them).

karg

[Edit]I really should take out debugging strings before I time stuff. Goes down to well under a second for 2.6mil tris. Plenty fast.

karg

[edited by - Karg on June 9, 2004 2:49:13 PM]

Eliminating discontinuities (T-junctions) in BSP?

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Eliminating discontinuities (T-junctions) in BSP?

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