[MacPorts] #57577: qt4-mac : set the graphicssystem via qtconfig

[MacPorts]

#57577: qt4-mac : set the graphicssystem via qtconfig
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 Reporter:  RJVB         |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:  haspatch     |       Port:  qt4-mac
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 There has been some discussion concerning flickering UI elements under OS
 10.14 in KDE4 applications leading to https://github.com/macports
 /macports-ports/pull/2974 .
 KDE4 has long forced raster mode for a variety of reasons, but apparently
 it causes or aggravates the flickering graphics problems under 10.14 .

 The pull request mentioned above simply removes the forced raster mode
 indiscriminately, i.e. also on OS versions where it is to be preferred.

 I've implemented an alternative where users can control the default
 graphics system used (native vs. raster vs. OpenGL) via Qt's own qtconfig
 utility (to be used with a modified patch to kdelibs4). I've set the
 default to "Native", evidently.

 I would have preferred a solution specific to KDE4 but achieving a similar
 user-friendliness would require a lot more work. It should be possible
 however to implement a setting controlled through qtconfig but used
 (applied) only by kdelibs4 (in the `KApplication` class).

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Ticket URL: <https://trac.macports.org/ticket/57577>
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