Re: depth sorting (bug 989156)

[Frank C <li...@si...>]

On 7-Aug-04, at 10:20 PM, James W. Walker wrote:

> I've been doing some experimentation on ways of doing depth sorting of 
> transparent triangles.  The choice of algorithms comes down to one of 
> those classic tradeoffs: do you want the job done right or do you want 
> it done right now?  But it seems clear that we can do better than what 
> we have now.
>
> ...
>
> 1. current Quesa comparison method, qsort
> 2. centroid comparison, qsort
> 3. barycentric comparison, selection sort after centroid qsort
>
> Method 1 (which Quesa currently uses) displays constant ugly flashing.
> Method 2 has much less flashing, though it is not hard to see sorting 
> errors much of the time.  This is of similar speed to method 1.
> Method 3 has only occasional errors, but is quite a bit slower.

Very nice!

#2 seems like an excellent quality/speed tradeoff. I did some tests 
with a more stressful mesh (approx 1600 triangles) and the occasional 
errors were totally acceptable with #2 while #1 was a massacre and 
about 5FPS slower. #3 ran at 0.1FPS, so I don't think it would be a 
good choice as the default setting, though it may make sense as an 
option for those who prefer accuracy over speed. Perhaps you can add a 
"sorting quality hint" via the Get/SetProperty API and use both #2 and 
#3?

I think #2 should work out well enough in real-world applications. 
Self-sorting a cube turns out to be a fairly difficult thing to do 
per-triangle.

Frank.