Bug#894462: paraview: edges are blotted [regression]

[Francesco Poli]

On Sat, 24 Feb 2024 21:13:25 +0100 Drew Parsons wrote:

> On 2024-02-24 12:40, Francesco Poli wrote:
[...]
> > Could you please forward it upstream, instead?
> > Thanks for your time and dedication!
> 
> 
> I don't understand what bug you want forwarded upstream.

Sorry, you're right: I haven't expressed myself clearly.
Let me try to do better.

> 
> FXAA anti-aliasing is enabled by default, but if you don't like you can 
> switch it off.
> Upstream have provided an option in Edit/Settings/RenderView so that you 
> can do that.

Exactly, and that's really good.

> What else do you want them to do?
> 
> Do you mean you want them to remove antialiasing entirely?

No, I don't.
I think anti-aliasing can be useful, so I agree that having it as a
possibility is really nice.

> That's not acceptable.

I agree with you on this.

> There are plenty of bug reports demanding antialiasing.

I can imagine...

> Do you want them to deactivate antialiasing by default?

No, I don't.

> I can't see that working well, for the same reason.

Sure, I think you're right.

> Do you want them to offer alternative antialiasing algorithms?
> Which ones?

I would like to see the FXAA algorithm improved, if that's possible at
all, so that it can provide the useful anti-aliasing, without that
unsightly "blot/smudge" effect on edges and on edge intersections.
Or, at least, without so much of that "blot/smudge" effect...

I am _not_ an expert of digital image processing, hence I am not sure the
algorithm can be improved on this respect.
Actually, I read on the Wikipedia article about fast approximate
anti-aliasing [FXAA], that one of the downsides is that "high contrast
texture maps are blurred". Assuming that the Wikipedia article is
reliable on this, I guess that edges and their intersections make for
high contrast elements on the visualization, so it's possible that this
"blot/smudge" effect is an inherent feature of the algorithm...

[FXAA]: <https://en.wikipedia.org/wiki/Fast_approximate_anti-aliasing>

Maybe the FXAA parameters can be tweaked to reduce the "blot/smudge"
effect.

I tried to play a bit with them (you can access them by clicking on the
gear button "Toggle advanced properties" in the "Render View" tab of
the Settings dialog window).
By reducing the "Endpoint Search Iterations" from the default value of
12 to 1, I have already obtained a significant reduction of the
"blot/smudge" effect. It has almost gone away, while the provided
anti-aliasing is still visible, I think.
See the attached image, for comparison with the previously sent ones.

Maybe better default values for the FXAA parameters could be set by the
upstream developers?



P.S.: Thanks for following up on this bug report and for your time.
      This is really appreciated.


-- 
 http://www.inventati.org/frx/
 There's not a second to spare! To the laboratory!
..................................................... Francesco Poli .
 GnuPG key fpr == CA01 1147 9CD2 EFDF FB82  3925 3E1C 27E1 1F69 BFFE
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