Problem in Carbon - Device Context Origin and BitBlt

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From this thread here
http://forum.lazarus.freepascal.org/index.php/topic,12172.msg188486.html
(see page 2 and 3)

a bug in Carbon Widgetset was found as reason for problem in virtual treeview:
"Device Context Origin is not respected in BitBlt under OSX"
http://bugs.freepascal.org/view.php?id=28689

Just posting here incase there are "Carbon" people here who knows their way around Lazarus Carbon widget set.

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This post summaries which code portions that might be relevant for a solution for the carbon device context origin / BitBlt issue
http://forum.lazarus.freepascal.org/index.php/topic,12172.msg189203.html#msg189203

Unfortunately, I have doubts if I will make any progress at solving it, but maybe someone else can. If I do succeed at fixing it I will post a followup