On Thu, 17 Apr 2008 13:15:42 -0400, Behdad Esfahbod wrote:
> On Thu, 2008-04-17 at 18:07 +0100, Gustavo J. A. M. Carneiro wrote:
> > > +1 too. Though opening the actual generated PDF in evince is always
> > > going to be a more reliable preview than rendering to a widget. There
> > > always will be bugs here and there, you know...
...
> Because as I said, "There always will be bugs here and there".
I think the "always" in Behdad's "there always will be bugs" is much
stronger than in his "[using evince] is always going to be a more
reliable preview".
> > You could claim quite the reverse. If print preview does not go through
> > App->Cairo->PDF->Cairo->Screen layers (would be only
> > App->Cairo->Screen), then users will not catch PDF/PS generation bugs so
> > soon, they only see the bugs appear on paper, and then it will be
> > convoluted by printer driver bugs, etc.
>
> That's what I meant.
Right. We do get to test more layers by doing the full
round-trip. And I also agree that's a good thing.
Interestingly, though, some of those layers can show bugs that are
unique to this preview environment. So here's at least one concrete
example where doing preview this way is actually less reliable.
I can write a program where both of these are correct:
Display to screen: App->Cairo->Screen
Print to PDF: App->Cairo->PDF
But the following is totally broken:
Print preview: App->Cairo->PDF->Cairo->Screen
And that's simply because there are bugs in poppler, which does the
PDF->Cairo step, and poppler isn't actually involved in either the
display-to-screen or print-to-pdf scenarios.
That's not to single out poppler. There are certainly bugs in any of
the stages, (App->Cairo, Cairo->Screen, or Cairo->PDF). And we
definitely need to just use this full-round-trip process and make it
as bomb-proof as possible.
And we do do that kind of round-trip testing within cairo's test
suite, and it does find poppler bugs in the PDF->Cairo stage. Here's
our tracking bug that shows what issues we've found so far:
Poppler does not yet handle everything in the cairo test suite
https://bugs.freedesktop.org/show_bug.cgi?id=12143
Any help on fixing those will be greatly appreciated of course, (and
will make any poppler-based print preview much more reliable).
-Carl
Attachment:
pgpF2PHY67gja.pgp
Description: PGP signature