Hi,
It's once again me, this time without a patch :-). I just want to
discuss some open issues that come into my mind after sleeping one night
over it, and this don't really depends completely on radial shading in
Splash, therefore I open a new thread:
After digging really deep into radial shadings the last four weeks there
are still a few open issues left:
I. Gfx::doRadialShFill
There were three different problems / bugs which causes me to spend
that enormous time implementing radial shading in Splash (probably
wouldn't have done it, if I could estimate that before :-) ):
a) Rendering artefacts because of overlapping circle clipping pathes in
http://www.acquerra.com.au/poppler/img_0.pdf
b) wrong calculation of extension range causing rendering regressions in
https://bugs.freedesktop.org/attachment.cgi?id=41506
c) wrong implementation of drawing larger extension circles causing
rendering regressions in the same PDF
These three problems cause rendering regression in each OutputDev which
hasn't implented radialShadedFill by its own or if in case it has
implemented it, it returns gFalse (this fits to CairoOutputDev, which
uses its implementation just to setup some datastructure but let the
rendering done by Gfx::doRadialShFill).
I myself encounter three main output devices:
1. PSOutputDev implements radialShadedFill and therefore does not have
the problems ahead (of course could have some other problems with it,
but that's then a problem of its own implementation)
2. SplashOutputDev implements radialShadedFill now by its own and will
not have these problems anymore after one of my patches will be committed.
3. CairoOutputDev will still have these problems.
So have a quick look at CairoOutputDev. In my opinion there are two
possible solutions for solving that:
a) CairoOutputDev implements radialShadedFill by itself. I'm not deep
enough in cairo to determine if this could be a possible way, perhaps
with some hints from me and / or Andrea.
But if this would be too heavy and / or the rendering regressions with
the first PDF (see here the wine glass) would be acceptable, I could
suggest another way:
b) I correct the bugs two and three in Gfx::doRadialShFill, the first
one is unfortunately not correctable in Gfx. The second bug is simply
correctable by a code fragment that already comes from cairo, which I
already use adapted successfully in my both patches for splash, for the
third bug I could adapt the different way of drawing larger extension
circles of my patch from saturday (therefore, once again, Albert, this
is an additional reason for regtest this older patch, too).
II. Speed an quality using radial shading in Splash:
I uploaded last weekend two patches for it with two different
implementation methods. The patch from sunday has definitely a better
quality but in a very few cases sucks in rendering speed than the patch
from saturday, which on the other hand has a poorer quality. Perhaps we
can find somehow a threshold value on which we can decide, wether method
should be used. This could be an additional reason to regtest both
patches, but commit only the patch from sunday with the "undef"ed code
so that it would be easy to implement this new behaviour later on.
I need not necessarily do the work of I or II, but if the community
means that I should do that, I suggest we open a new bug with this two
PDF. I worked nearly every free minute on solving the problems in splash
the last four weeks, and the patch is still not committed and there
could of course be some work left (hopefully none or only a few), so I
want to take time out, and therefore a bug report is reasonable.
Thomas
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