title: What is responsible for font rendering on linux?
body: <p>I am sorry if my question is a bit vague.  I am trying to understand where to look for my problems.  I have a regression test suite that captures and compare the screen.  It seems like whenever we do some kind of library upgrade the regression tests would fail.   Our font settings are the same.   The difference would be like the graphics card upgrade (driver), window manager upgrade, or just third party library upgrade (for example Qt library).  From human visual testing, the fonts look almost identical, but if I do pixel to pixel comparison, it would show that the snapshots are different.  Does anyone have insight how the fonts are rendered ?  </p>