From: Angus Dorbie (dorbie++at++sgi.com)
Date: 11/08/2000 20:26:16
We haven't defined the feature set for Performer 2.5 yet.
On the technical side there are several schemes which could deliver this
type of capability. The key is to be able to page the cliptexture
database representation used by customers today with minimal
modifications to the database or application.
The various options have different performance and quality implications.
For example, it turns out that if we retain intact the torroidal paging
scheme in Performer cliptextures but instead of a cliptexture we use
several independent texture objects, one for each roaming level in the
clip texture, we can apply the appropriate highest available level of
detail texture to primitives based on a simple texture coordinate bound
box test (including invalid border) and use a texture matrix to adjust
for the specific level being used. Texture wrapping automatically gives
you a kind of modulo addressing for the tile region if you want to think
of it that way. Thanks to Robert Subr for his insight here.
It is a low quality solution and requires messing around with texture
handles (possibly in the apply method) and coordinates (probably using a
texture matrix), but it would give you load balanced paging of a
cliptexture database. Possible hardware enhancements to improve this
might include being able to address different texture objects as a
function of level of MIP with the right central region addressing from
one image to another. This would avoid aliasing on minified tiles or at
least avoid having to redundantly page the MIP levels for each tile. If
in doing so you clamped per MIP level then you'd effectively have 'real'
clip mapping but that would in essence require a full clipmap support in
hardware, just by a subtly different name really.
There are other schemes which are more explicitly tile oriented which
might be more flexible but require implementing additional texture
paging code in Performer.
Cheers,Angus.
Thomas Klinedinst wrote:
>
> Does anyone know the roadmap for cliptexture support on hardware other
> that the Onyx2/3 Reality/IR3 systems? Will there ever be support for
> cliptextures on the Octane2 VPro graphics? How about the SGI Linux
> workstations? Is this a political/sales issue to try and sell Onyx
> level systems or is there a significant technical problem which makes
> this challenging on other hardware platforms? Are there any other
> equivalent software capabilities for these other platforms that cost
> less than than an IR itself?
>
> Any help in this area would be useful since our customer base will no
> longer support Onyx level hardware purchases.
>
> Thanks,
> Tom Klinedinst
> Sarnoff Corporation
> tklinedinst++at++sarnoff.com
> 609-734-2624
>
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