On Mon, Aug 31, 2020 at 07:17:30PM +0100, Ken Moffat via blfs-dev wrote:
> On Mon, Aug 31, 2020 at 08:04:37AM -0500, Marty Jack via blfs-dev wrote:
> > On Mon, 31 Aug 2020 01:44:03 -0500 Ken Moffat via blfs-dev wrote:
> > > On Mon, Aug 31, 2020 at 06:48:47AM +0100, Ken Moffat via blfs-dev wrote:
> > 
> > I build libreoffice 7 with gcc and without clang, which I do not have 
> > installed.  I also do not have skia installed.
> > It generates
> > 
> > checking whether to build Skia... yes
> > checking for clang... no
> > configure: WARNING: Clang compiler not found.
> > 
> > Takes about an hour on my i5-8600 for make build-nocheck.
> > Clearly they may change this in future but this suggests that clang need 
> > not be required by the book.
> 
> Hmm.  Technically it is 'Recommended'.  All my systems do have clang
> and I don'y have a log from the failed build, all I know for certain
> is that it tried to use clang when building skia, and failed because
> clang does not (in current release) support my flags.
> 
> I'm guessing that your log can be interpreted as
>  should I build skia : yes (default)
>  do you have clang : no
>  ok, cannot build skia, issue a warning.
> 

Marty is right: if clang is not present, Skia will still be built
(assuming it has not been separately installed) - but using code
which is slower in software fallback mode (skia also supports vulkan
acceleration for hardware rendering).

The definitive answer of whether Skia will be built on a particular
run is in config.log.

The diff between logs from a default build and a build where I
disabled Skia were too big for me to identify what, if anything, was
compiled instead.  I can see references to /usr/include/cairo in
both builds.

Apparently the slower code is because Skia is only tuned for clang,
and because of the way it is written less code will be, or at least
in the recent past was, inlined by gcc.  And the reason for using
Skia in LO was because of a bug report about slow scrolling in calc
*if shapes are visible*
https://bugs.documentfoundation.org/show_bug.cgi?id=131697

So for people who put graphics in their spreadsheets Skia is
obviously beneficial.

Anyway, clang is still recommended for Skia, but for most of us it
probably won't make any difference.  For myself, disabling Skia
doesn't seem to impact scrollign in my own spreadsheets but perhaps
in future I'll look at hiding clang when I come to build
libreoffice.

ĸen
-- 
I could not live without Champagne.  In victory I deserve it, in
defeat I need it.  -- Churchill
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