[Lazarus] Get JPEG from TAChart in CGI app

[Mattias Gaertner]

On Mon, 21 Mar 2011 11:53:52 +1000
Alexander Klenin <klenin at gmail.com> wrote:

> On Mon, Mar 21, 2011 at 08:41, Mattias Gaertner
> <nc-gaertnma at netcologne.de> wrote:
> > On Mon, 21 Mar 2011 04:58:18 +1000
> > Alexander Klenin <klenin at gmail.com> wrote:
> >> Hm. For me GUI means "graphical user interface" -- that is, windows (aka forms),
> >> interacting with mouse, etc.
> >> I have just committed a demo which does not have any of this,
> >> and yet successfully draws TChart to a file -- see previous mail.
> >> Maybe for you GUI means a different thing?
> >
> > Yes. The GUI of the screen.
> > By accessing the LCL canvas you access the widgetset (gtk2) which
> > accesses the current screen. For example the gtk2 asks for
> > theme, fonts, screen color depths and sub pixel rendering parameters.
> > A cgi program has no screen.
> 
> It is ok to ask for all these things since thay are necessary to
> render the chart.
> However, the fact they are unconditionally taken from the screen is IMO
> a deficiency of either GTK or LCL-GTK.

The display error comes from the gtk.


> As you can see in this thread, as soon as this deficiency is worked around,
> (in this case, by using Xvfb utility), the problem is solved.

I wonder how much overhead it is for a cgi program to start gtk on xvfb
compared to a fpcanvas program.


Mattias