When I open the test PDF in atril (the Mate desktop version of evince) and 
change the window size (with 'fit page width'), once I get below about 80%, 
small changes make the bars of the staff go up and down, and not all of the 
bars of the staff shift equally, so the space between the bars is not equal, 
and that might contribute to the effect that the notes are misplaced. I am not 
sure, but it seems as if it is not antialiasing the bars. When you reduce the 
image to the point where pixels are significant and the total number of pixels 
is not the exact amount to leave the same number of pixels between each bar, 
rounding can't create more pixels. You need to simulate fractional pixels 
through antialiasing. The 'w' command in PDF sets the line width. It looks like 
it is drawing lines of 0.4, 0.65, 0.8, and 1 point. The tests for thinLineMode 
are in splash/Splash.cc.


William


________________________________
From: poppler <[email protected]> on behalf of 
[email protected] <[email protected]>
Sent: Sunday, March 26, 2017 12:34 PM
To: Albert Astals Cid; [email protected]
Subject: Re: [poppler] Scaling factor and placement accuracy

>> ourParent->document->setRenderHint(Poppler::Document::Antialiasing);
>> ourParent->document->setRenderHint(Poppler::Document::TextAntialiasing
>>ourParent->document->setRenderHint(Poppler::Document::ThinLineSolid);

>Tried thin line shape instead of thing line solid?

Thanks, Albert, I just tried it, same result.

I spent a couple hours last night trying to find the area of code that does the 
actual placement without any real luck, to see if there is any kind of rounding 
issue.   I saw a lot of other possible areas like anti-aliasing, but basically 
got lost in the code because I don't know enough to know what is actually 
inside the PDF (I tried PDFStreamDumper and can see what's inside, and even 
seeing it I do not understand it).

So far making the x/y scale factor integral appears to avoid the problem; it's 
hard to prove a negative, but I have not seen it occur in that case. This just 
very slightly throws off the desired size I want, and I just needed to put a 
proper color border into the overall page to avoid showing an outline, so it's 
very workable for what I want, if it keeps working.

Thanks again,

Linwood
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