inkscape fails to print thin lines to PDF

When using very thin lines, export to PDF may not show them all.
Below 0.018mm lines are missing. Especially curved lines.

Also the print preview does not show them.

This is with inkscape-0.48.4

Created an attachment (id=537342)
samle svg file

boxes and circles with different line width. This svg also renders nicely when loaded in firefox. From there I can print to PDF with all elements, except for width 0.001mm (acceptable)

Created an attachment (id=537343)
pdf printed with firefox

please note that
a) scaling is ca 2% too small, although 100% was selected
b) the final box and circle are missing. 0.001mm is maybe just too small.

(not sure if these qualify as additional bugs)

Created an attachment (id=537344)
pdf printed with inkscape

Note that

a) all boxes are there (even the 0.001mm line width)
b) circles are missing with line width below 0.018mm

forwarded to https://bugs.launchpad.net/inkscape/+bug/1174909 -- not sure if this is SUSE-specific at all.

Apparent workaround:
Downgrade to cairo-1.12.2 -- we currently ship 1.12.8 which causes the issue.

(In reply to comment #5)
> Apparent workaround:
> Downgrade to cairo-1.12.2 -- we currently ship 1.12.8 which causes the issue.

The issue is also present with cairo-1.12.15 (as seen in home:pontostroy:X11)

Since 1.12.3, cairo cannot render fine lines to pdf. 1.12.2 was the last version that worked.

http://cgit.freedesktop.org/cair/diff/?id=bdf83008f4b2c723fd8e65e2a92bc47a2e7bc442

introduced this code in cairo-compositor.c:_cairo_compositor_stroke

   if (_cairo_pen_vertices_needed (tolerance, style->line_width/2, ctm) <= 1)
        return CAIRO_INT_STATUS_NOTHING_TO_DO;

The idea was to avoid lines that would be invisible when rasterized. While this is a valid logic for raster backends, it is a bad idea for PDF output. There we want to see all fine lines.

My specific use case is generating a lasercutter drawing for an Epilog Zing laser with inkscape. There the hardware would raster anything thicker than 0.02mm, and cut 0.01mm or below. 1.12.3 skips lines below 0.036mm, 1.13.1 skips lines below 0.018mm -- which is still not enough to safely drive my lasercutter.

See also https://bugs.launchpad.net/inkscape/+bug/1174909

Check out the attached reproducer.

Created attachment 97205
reproducer

Created attachment 97206
Example output from the reproducer with missing objects.

Created attachment 97207
Example output from the reproducer when good.

Reported upstream https://bugs.freedesktop.org/show_bug.cgi?id=77298

Created attachment 97220
suggested fix.

Please double check if num_vertices == 1 should never be done (for PDF).

I am not sure why this was introduced at all. With 1.12.2 the lowest num_vertices value was 4, which assured that all objects are rendered to the PDF.

Created an attachment (id=586045)
suggested fix.

Created attachment 97247
Suggested fix. Different approach.

Contributed by Patrick Himmelmann. Now we have something to discuss. Maybe we find a third alternative, so that the logic for raster backends continues to discard small objects, but the logic for vector backends includes everything?

Could somebody review the suggested change there?

This is not really a pdf specific problem. We need to always pass strokes through to the vector backends no matter how thin. I don't know the best way to do this as I am not familiar with that code that these patches modify.

Juergen,

I am inclined adding this patch to GNOME 3.14 for openSUSE 13.2;

I assume you have been running on one of the upstream solutions for a while now? Did you see any negative impacts?
Which of the two solutions are you operating? I'll just go with the one you tested already.

I am running with our own patches.
Did you see a working upstream solution?

I see that https://bugs.launchpad.net/inkscape/+bug/1174909 just got downgraded from confirmed to unknown.

Please pull into Gnome 3.14

(In reply to Sebastien Bacher from comment #6)
> Could somebody review the suggested change there?

Patrick's version is best, please go ahead with this patch!

he, first look, then talk, right?
We actually already have that patch in Factory and openSUSE 13.2.

So from the openSUSE perspective, I am closing the bug as FIXED and hope for upstream to come up with an even better solution matching them.

@Chris Wilson et all:

I'd like to raise priority on this issue.
We know the issue to exist for several years now on Linux systems. Recently we see more and more Windows systems to suffer from the same issue. The attached patch is simple and fixes the issue.

Is there anything I can do to summon a cairo maintainer here?

is there anyone wanting to review that one?

Created attachment 118380
Don't cull thin lines on vector backends

The patch didn't work for my test case and broke many other tests.

Attached is a new patch that seems to fix the bug. The patch ensures a minimum line width when calculating stroke extents on vector backends.

Created attachment 118381
cairo test for thin lines

This patch contains a cairo test for thin lines.

Created attachment 118385
attachment-30721-0.html

This seems excessively complex, rather than having the later handler (the
one turning a non-zero float into a zero fixed) be patched instead. I
figure it would be correct for all backends to turn very tiny but non-zero
line widths into the smallest ones they can render.

On Mon, Sep 21, 2015 at 5:18 AM, <email address hidden> wrote:

> *Comment # 12 <https://bugs.freedesktop.org/show_bug.cgi?id=77298#c12> on
> bug 77298 <https://bugs.freedesktop.org/show_bug.cgi?id=77298> from Adrian
> Johnson <email address hidden> *
>
> Created attachment 118381 <https://bugs.freedesktop.org/attachment.cgi?id=118381> [details] <https://bugs.freedesktop.org/attachment.cgi?id=118381&action=edit> [review] <https://bugs.freedesktop.org/page.cgi?id=splinter.html&bug=77298&attachment=118381>
> cairo test for thin lines
>
> This patch contains a cairo test for thin lines.
>
> ------------------------------
> You are receiving this mail because:
>
> - You are watching the QA Contact of the bug.
>
>

(In reply to Bill Spitzak from comment #13)
> Created attachment 118385 [details]
> attachment-30721-0.html
>
> This seems excessively complex, rather than having the later handler (the
> one turning a non-zero float into a zero fixed) be patched instead. I
> figure it would be correct for all backends to turn very tiny but non-zero
> line widths into the smallest ones they can render.

We don't want to alter the line width on the vector backends. If a 0.001mm line width is specified for pdf that is the line width it should use. My patch only alters the line width when the extents are measured for the purpose of culling 0 width/height objects.

I've commit my patch and testcase.

@Adrian - the commit broke the quartz backend (and based on comments on irc the gl backend too):

  CC cairo-quartz-surface.lo
cairo-quartz-surface.c:2265:12: error: too few arguments to function call, expected 5, have 4
                         content);
                                ^
./cairoint.h:1335:1: note: '_cairo_surface_init' declared here
cairo_private void
^
./cairo-compiler-private.h:133:27: note: expanded from macro 'cairo_private'
#define cairo_private cairo_private_no_warn cairo_warn
                            ^
./cairo-compiler-private.h:120:31: note: expanded from macro 'cairo_private_no_warn'
#define cairo_private_no_warn __attribute__((__visibility__("hidden")))
                                ^
1 error generated.
make[3]: *** [cairo-quartz-surface.lo] Error 1

Should be fixed now.

(In reply to Adrian Johnson from comment #17)
> Should be fixed now.

Thx a lot - build fix confirmed for quartz, quartz-image, xml and tee surface backends.

It seems the GL backend still doesn't compile as a couple uses of _cairo_surface_init weren't updated:

cairo-gl-source.c:76:5: error: too few arguments to function ‘_cairo_surface_init’
cairo-gl-source.c:103:5: error: too few arguments to function ‘_cairo_surface_init’

There's also a similar error for _cairo_path_fixed_approximate_stroke_extents():

cairo-gl-msaa-compositor.c:584:6: error: too few arguments to function ‘_cairo_path_fixed_approximate_stroke_extents’