Andrew Vincent (andrewv++at++canberra.sgi.com)
Thu, 5 Feb 1998 12:11:04 +1100
Andrew
-----Original Message-----
From: Angus Dorbie [SMTP:dorbie++at++multipass.engr.sgi.com]
Sent: Wednesday, February 04, 1998 4:44 PM
To: Charles Seberino; info-performer++at++sgi.com
Subject: Re: Problem displaying objects that are sub-pixel size
This is purely an aliasing problem, the polygons should actually
average out at about the right density due to point sampling
IrisGL used to cull < .5 pixel^2 area polygons but I don't think
OpenGL does this.
You should enable multisample anti-aliasing on the iR after choosing
a visual with 8 multisamples.
Call pfAntialias(PFAA_ON) from your draw process.
If you don't want full scene anti-aliasing then you should try
enabling blending and calling glEnable(GL_POLYGON_SMOOTH)
before drawing the degenerate polygons and disabling afterwards to see
if this helps.
Cheers,Angus.
On Feb 3, 10:39am, Charles Seberino wrote:
> Subject: Problem displaying objects that are sub-pixel size
> I am having a problem displaying small polygons, which when viewed at long
> distances, don't (or rarely) appear on the screen. Here is what I am trying
to
> do:
>
> Creating several hundred OPENGL GL_QUADS with the same texture applied to
each
> of them. The polygons are drawn so that they are always facing the
> display(billboarded). The problem I get is when I view the polygons(1 in^2
> each) from far away, the individual polygons only take up from 1-4% of a
screen
> pixel. The polygons are all close to each other so I should be seeing the
> cumulative effects of all the objects(a particle cloud), but I only get a
pixel
> every so often. I am using a luminance-alpha texture to display the square
as
> a sphere. I have tried changing the minification filters, but none give the
> correct result.
>
> What can I do to get these objects to appear as they should?
>
> I decided not to go the route of creating several hundred pfGeoSets/pfGeodes
> (maybe pfBillboards) because I thought it would be more time consuming and
not
> give any added benefit.
>
> Running on Onyx2 IR pf2.1
>
> Any suggestions?
>
> Charles
>
> --
> -----------------------------------------------------------------------
> Charles Seberino Raytheon Missile Systems Company
> seberino++at++or_lab.tu.hac.com phone: (520) 794-7078
> fax: (520) 794-8625
> =======================================================================
> List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/
> Submissions: info-performer++at++sgi.com
> Admin. requests: info-performer-request++at++sgi.com
>-- End of excerpt from Charles Seberino
--
"The ultimate measure of a man is not where he stands
in moments of comfort and convenience, but where he
stands at times of challenge and controversy."
-Martin Luther King, Jr.
=======================================================================
List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/
Submissions: info-performer++at++sgi.com
Admin. requests: info-performer-request++at++sgi.com
===================================List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/
Submissions: info-performer++at++sgi.com
Admin. requests: info-performer-request++at++sgi.com
This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:56:44 PDT