[Qgis-developer] Wiki page/area for 'Building QGIS from scratch'

[Mark Johnson]

>> Can you clarify on which systems you are working and which dependencies
cause headaches?
In my case I am working on an old machine, where many things have been
installed in the past and cause conflicts. So until a new machine can be
bought I am attempting to get this done in a custom application directory,
where QGIS is then called from a script where the needed environment vars
are set so that everything needed is found first.
In my case it is since there are QT3, QT4 and older QT5 installed.
So a separate, clean,  QT5 is needed.

At present I have everything compiled, but QGIS3 fails due to something,
some complaining about different libpng's being found:

# libpng warning: Application was compiled with png.h from libpng-1.6.10
# libpng warning: Application  is  running with png.c from libpng-1.2.56
# libpng error: Incompatible libpng version in application and library

Here I assume the default libcairo loads libpng-1.2.56, which QT5 used
libpng-1.6.10,
which is installed in /usr/local/lib for librasterlite2.

So at the moment I have installed libcairo using libpng-1.6.10 in
/usr/local/lib, and recompiling QT5 using the internal PNG/JPEG libs.

>>In many situations, a build of Qt is not required and doing this
requires deep understanding of all the involved libraries.
Yes and the idea a Wiki page/area for 'Building QGIS from scratch' could
assist in making that easier.

Mark
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