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

[Matthias Kuhn]

On 03/17/2017 05:58 PM, Mark Johnson wrote:
>>> 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.

What would be interesting for such situations would be something like
AppImage. I tried that some time ago but stopped because I got
sidetracked. It would still be very interesting for a wider purpose.

Some discussion can be found here:
https://github.com/qgis/QGIS/pull/3784

If you manage to get this running, we will be able to offer
cross-distribution downloads.
I'll buy you some coffees or beers for that.

> 
> 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.

I suspect these kind of conflicts differ from system to system and
documenting them on a page could end up in a collection of red herrings.
(I might be wrong here).

> 
>>>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.

Feel free to start working on this :-)

Matthias