there are two important bits here:
1) report all driver bugs
2) D3D fog
1) report all driver bugs.
this is SO important. if all ISVs dont report driver bugs they find, the
quality of the drivers never gets better. please take the time to report
these.
Most IHVs do have helpful dev-rel folk and want to hear this sort of
thing to make their products better.
they cant if we arent vigilant, we are all in this together.
please.
2) D3D fog.
D3D implements two types of fog: vertex fog and pixel fog.
pixel fog ( sometimes called table fog ) should be preferred over vertex
fog since it appears better, as long as the driver correctly implements
it. note the key statement "as long as the driver correctly implements
it"****. it appears better since its calculated per-pixel instead of
calculated per-vertex and then iterated.
pixel fog comes in two flavors:
1) Eye-relative pixel fog ( or w-fog indicated by the
D3DPRASTERCAPS_WFOG caps bit ) is preferred since it avoids certain
fogging artifacts due to non-linear distribution of z values in the
z-buffer.
1) z-based pixel fog. If w-fog isnt supported you get z-based pixel fog.
if the driver doesnt implement pixel fog, fall back to vertex fox.
vertex fog comes in two flavors:
1) range based fog ( indicated by the D3DPRASTERCAPS_FOGRANGE caps bit )
uses the actual distance from the viewpoint to the vertex rather than
the depth of the vertex; avoiding some rotational artifacts. If
range-based fog isnt supported, you again get z-based fog.
2) application fog. the application must use its own fog calculations
when not using the D3D TnL pipeline. the fog factor is calculated and
placed in the alpha component of the specular color, making specular
really RGBF in that case.
Regardless of which type of fog, pixel or vertex, you use - your
application must provide a compliant projection matrix ( what the docs
call a W-Friendly Projection Matrix ) to ensure that fog effects are
properly applied. This restriction applies even to applications that do
not use the Direct3D transformation and lighting engine. If the
projection matrix isn't compliant with this requirement, fog effects are
not applied properly. This is covered in more detail in the D3D doc.
so, to avoid really bad artifacts the order an application should prefer
fog features is:
pixel w-fog
vertex range-fog
pixel z-fog
vertex z-fog
application fog.
if the application isnt using the D3D TnL pipeline ( which is quite good
and has per-processor specific optimizations ) then its highly likely
that application fog will produce the most uniform results since you
control your own destiny by informing the iterator what values to
iterate at each vertex.
and, as always, one must be aware of the bad drivers out there which
would modify that order of feature preference.
****GetDeviceIdentifier allows a mechanism to identify card/drivers that
do not comply with the spec, and provide a last-chance method to
fallback. Applications that depend on certain functionality should
consider maintaining an internal list of offending card/drivers and
performing a fall-back mechanism to ensure correct visual appearance.
> -----Original Message-----
> From: Kelvin Chung [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, May 17, 2001 2:57 PM
> To: [EMAIL PROTECTED]
> Subject: Re: [JAVA3D] Fog (Linear) Differing Results
>
>
> >X-Sender: [EMAIL PROTECTED]
> >Date: Thu, 17 May 2001 17:49:32 -0400
> >To: Kelvin Chung <[EMAIL PROTECTED]>
> >From: Mark Ferneau <[EMAIL PROTECTED]>
> >Subject: Re: [JAVA3D] Fog (Linear) Differing Results
> >Cc: [EMAIL PROTECTED]
> >Mime-Version: 1.0
> >
> >Kelvin,
> >
> >In the body of the email I indicated J3D (Java3D) 1.2.1_01
> for both OGL and
> >D3D. I think, therefore, that this is a driver
> issue--although I see it
> >across different machines, boards, and operating systems.
> So essentially I
> >should probably not rely on fog looking reasonably consistent across
> >different platforms or graphics boards.
> >
> >Therefore another method will have to be used to achieve the same
> >effect. Would you agree with that statement?
> >
> Not sure. If it is a driver bug we should notify the graphics
> vendor to fix it. I suppose driver should implement it
> according to the fog formula.
>
> At least under Sparc Solaris the fog effect are consistent.
>
> - Kelvin
> -----------------
> Java 3D Team
> Sun Microsystems Inc.
>
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