[poppler] Scaling factor and placement accuracy

[pqt at LEFerguson.com]

Thomas Freitag wrote on Tuesday, March 28, 2017 5:28 AM:

>>But probably you can get a better result when you render it in a high resolution
>>(i.e. 600 dpi) and then resize it for displaying. I played a little bit around with it,
>>the  stave lines will get different shapes then, but at least they are centered to the
>>stave notes.

I experimented with this up to 5 times the native monitor resolution and it actually made things worse.  At twice it completely solved the position problem, but lines disappeared. I think they get rendered as a single pixel, and then when the QImage is scaled, despite anti-aliasing being set, sometimes they vanish entirely, sometimes almost entirely, and sometimes they end up strangely double wide.  I even tried one 10x  (1250dpi) and attached it for your amusement.  I don't even think I could do 2x on the Raspberry Pi due to memory and speed since 2x is 4x the data.  So I'm back to native resolution, using larger notes, and using integers and crossing my fingers.  Using integers does help, not sure why, but it's not a complete solution.

Thanks for the background material.

I do still think there's a rounding issue somewhere.  Adobe Reader works at the same scale.  An example is attached if curious. These have about 30% larger notes (which helps). It's literally only a pixel different (the two E's on the middle staff), but Adobe is always right on the line.



Thanks again,



Linwood
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