RE: [Algorithms] Isometric 2D drawing order.

[Tom F. <to...@mu...>]

It's entirely possible that doing this:

1) decent high level cull
2) z-buf on
3) render base front to back
4) render buildings and sprites
5) sort alpha tris back to front
6) z-buf write off
7) render alpha tris


Will be quicker. Despite the fact that you have the Z-buffer on, by drawing
front to back you will get very fast Z-rejects for hidden stuff, and the
framebuffer won't be touched, and the textels won't be fetched. This can be
quicker, depending on your level of overdraw.

Turning the Z-buffer write off (you still need the read) for alpha stuff is
standard practice. Since they are sorted anyway, there's no need to write
the Z values back, and it saves a bit of bandwidth.


Having said all that, the majority of 2D drawing code is CPU-bound, not
rasteriser-bound, so it may all be completely irrelevant.


Tom Forsyth - purely hypothetical Muckyfoot bloke.

This email is the product of your deranged imagination,
and does not in any way imply existence of the author.



> -----Original Message-----
> From: Martin Slater [mailto:Ma...@cs...]
> Sent: 17 November 2000 16:02
> To: gda...@li...
> Subject: RE: [Algorithms] Isometric 2D drawing order.
> 
> 
> 
> Cheers for the info, (and thanks to brian for starting it off)
> 
> As I'm not looking for ground breaking speed (yet) the best 
> bet for speed to
> implement has to be 
> 
> 	1) decent high level cull
> 	2) z-buf off
> 	3) render base back to front
> 	4) z-buf on
> 	5) render buildings and sprites
> 	6) sort alpha tris back to front
> 	7) render alpha tris
> 
> Only aiming at dx at the mo with only a token thought to users of old
> systems so I can't imagine this will be too slow. Time to try it out..
> 
> 
> Martin
> 
> > -----Original Message-----
> > From: gda...@li...
> > [mailto:gda...@li...]On 
> Behalf Of Tom
> > Forsyth
> > Sent: 17 November 2000 15:31
> > To: gda...@li...
> > Subject: RE: [Algorithms] Isometric 2D drawing order.
> > 
> > 
> > Further caveat - (1) is only true if they _all_ use ONE:ONE. 
> > If half use
> > standard alpha-blend modes, they all need to be sorted 
> > properly. Well, OK,
> > you don't need to sort ONE:ONEs with each other, just with 
> > the non-ONE:ONEs,
> > but that's almost the same amount of work by the time you 
> > have written a
> > sorting routine, etc. and I suspect the code that tests 
> > whether two facets
> > do or don't need to be sorted against each other is going to 
> > be slower than
> > just doing the sort for everything.
> > 
> > 
> > Tom Forsyth - purely hypothetical Muckyfoot bloke.
> > 
> > This email is the product of your deranged imagination,
> > and does not in any way imply existence of the author.
> > 
> > 
> > > -----Original Message-----
> > > From: Tony Cox [mailto:to...@mi...]
> > > Sent: 17 November 2000 12:13
> > > To: gda...@li...
> > > Subject: RE: [Algorithms] Isometric 2D drawing order.
> > > 
> > > 
> > > Almost, but not quite. You still need to sort the alpha polygons
> > > back-to-front amongst themselves, *unless*
> > > 
> > > (a) They use a blending mode like ONE:ONE which does not 
> > need sorting,
> > > or
> > > (b) They are unfiltered 1-bit alpha with alpha-testing 
> (i.e. simple
> > > masks), where you can use the alpha testing to do the right 
> > thing on a
> > > per-pixel basis to the z-buffer. 
> > > 
> > > If you have semi-transparency, then you have to sort.
> > > 
> > > Of course, you can do a very rough sort, and hope that your alpha
> > > primitives are sparse enough that the result is right enough 
> > > of the time
> > > that nobody notices the odd error.
> > > 
> > > Tony Cox - DirectX Luminary
> > > Windows Gaming Developer Relations Group
> > > http://msdn.microsoft.com/directx
> > > 
> > > 
> > > >Just batch em up and render after everything else should do it,
> > > shouldn't
> > > >it?
> > > >
> > > >Martin
> > > >
> > > >> -----Original Message-----
> > > >> From: gda...@li...
> > > >> [mailto:gda...@li...]On 
> > > >> Behalf Of Ville
> > > >> Miettinen
> > > >> Sent: 17 November 2000 11:31
> > > >> To: gda...@li...
> > > >> Subject: RE: [Algorithms] Isometric 2D drawing order.
> > > >> 
> > > >> 
> > > >> Vanilla z-buffer does not handle alpha-blending 
> properly without
> > > >> back->front sorting. Thus, you need to apply some 
> algorithm (such
> > > >> as the one described below) to determine the correct drawing
> > > >> order. 
> > > _______________________________________________
> > > GDAlgorithms-list mailing list
> > > GDA...@li...
> > > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
> > > 
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