Re: [Algorithms] Depth-Sorting Axis-Aligned Boxes

[Richard M. <mi...@tr...>]

I may be missing something, but can't you just do a sort based on their 
furthest point along the camera axis?

i.e. transform into view space, then sort by furthest Z coordinate.

-- 
()()      Richard Mitton
( '.')
(")_(")       Beard Without Portfolio :: Treyarch


----- Original Message ----- 
From: "metanet software" <met...@ya...>
To: <gda...@li...>
Sent: Saturday, August 01, 2009 7:05 AM
Subject: [Algorithms] Depth-Sorting Axis-Aligned Boxes



This is a variation of the famous "isometric depth-sorting" problem: I have 
a 3D scene composed of axis-aligned boxes, viewed with an oblique/cabinet 
perspective ( http://en.wikipedia.org/wiki/Oblique_projection ).

Sadly I don't have a z-buffer, so I need to determine a way to sort the 
boxes back-to-front. The boxes will all be non-overlapping, although they 
may be touching, and will move smoothly (i.e not by grid-sized steps as is 
common in some games).

Is there a simple solution to this problem? I.e a formula which considers 
the extents and/or a reference point on each box to produce a back-to-front 
order? Or am I stuck with the general solution: build a BSP tree?

Would it help to consider individual faces rather than boxes? (It seems to 
me that this wouldn't help, since each face can be considered a box with 
size=0 along one axis).

Any suggestions or references would be most appreciated; all of the 
"isometric" stuff I've found via Google seems to be a big mess -- the 
algorithms which do work only work for objects which are all tile-sized and 
move in tile-sized increments.. which is just a special case of BSP (i.e the 
scene is essentially cut up by the grid).

thanks,
raigan


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