[cairo] [SVG] a8-mask failure

[Carl Worth]

On Thu, 20 Mar 2008 18:50:43 +0100, Emmanuel Pacaud wrote:
> The libpng warning is "PNG warning = Ignoring attempt to write bKGD
> chunk out-of-range for bit_depth".
>
> I'm not sure to like the "upgrade" of the warning to a cairo error. And
> the suppression of the PNG warning makes the debugging harder than it
> should.
>
> Do we really want to hide them ? Is there a good reason to make cairo
> fail on something that the libpng developers consider a simple
> warning ?

Here's the commit that gave us the upgrade of libpng warnings into
errors:

commit c06d929325710c1a2cbecb8a64803ca8e1ffbec0
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Thu Feb 28 16:07:57 2008 +0000

    [cairo-png] Further hardening against malloc failures.

    On some OOM paths, libpng raises a warning as opposed to an error,
    these were not being propagated back to the caller. We were also not
    checking that we did not overwrite a pre-existing error status when
    raising an error whilst performing I/O.

That sounds like there are bugs in libpng where it's returning a
warning though it should be returning an error. And the workaround for
this is causing the problematic behavior for a8-mask with cairo-svg.

If nothing else, we've got a single commit to revert if really
necessary.

> And more important, does someone here know how to fix the warning ?

But yes, this is the most important part. Let's try to get this fixed
so we can avoid these warning-handling code paths entirely. (But no, I
don't have any idea yet what needs to be changed here.)

-Carl
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