[cairo] PDF Issue in OS X Preview

[Behdad Esfahbod]

On Wed, 2006-10-25 at 18:28 -0400, Ryan Schmidt wrote:
> On Oct 25, 2006, at 11:55, Ken Treis wrote:
> 
> > I'm generating PDFs using the Ruby bindings and cairo-1.2.4.  
> > Everything works fine for me until I try to set scaling. The  
> > resulting PDF files look fine in Acrobat Reader but not in OS X  
> > Preview.
> 
> [snip]
> 
> Thanks for writing. I too reported a problem with cairo-generated  
> PDFs which looked fine in Adobe Reader but not OS X Preview. I'm not  
> sure if your case is the same as the one I was seeing. My problem was  
> that my PDFs are generated by graphviz, and I was unsure if the  
> problem was in cairo, graphviz, or Mac OS X's PDF renderer. Your  
> message gives me hope that it might be a cairo problem after all.
> 
> Unfortunately we didn't get very far in trying to solve the problem I  
> reported:
> 
> http://lists.freedesktop.org/archives/cairo/2006-July/007344.html
> 
> I did get far enough to see that it looks like Preview *is* rendering  
> the missing curves, just not at the desired offset:
> 
> http://lists.freedesktop.org/archives/cairo/2006-July/007463.html
> 
> Note that the glyph difficulties reported in the latter mail have  
> already been resolved in the current version of cairo; only the curve  
> offset problem remains for me.
> http://cairographics.org/cgi-bin/mailman/listinfo/cairo

This is a bug in cairo.  The generated PDF output from cairo:

10 M 100 100 m 100 200 l q 2 0 0 2 0 0 cm
S Q

is undefined according to the PDF spec version 1.6.  According to Figure
4.1 Graphics Objects on page 167, all gstate manipulations should occure
before path construction that should be followed by path-painting
operations.  It further clarifies on the following page:

"Note: A content stream whose operations violate these rules for
describing graphics objects can produce unpredictable behavior, even
though it may display and print correctly."

and:

"A graphics object also implicitly includes all graphics state
parameters that affect its behavior. For instance, a path object depends
on the value of the current color parameter at the moment the path
object is defined. The effect is as if this parameter were specified as
part of the definition of the path object."


Simply moving the cm operator before path construction should fix it:

10 M q 2 0 0 2 0 0 cm 100 100 m 100 200 l
S Q


Any takers?

-- 
behdad
http://behdad.org/

"Commandment Three says Do Not Kill, Amendment Two says Blood Will Spill"
        -- Dan Bern, "New American Language"