[PATCH] compositor-headless: Report a more realistic physical size

[Simon Ser]

> On Thu, 12 Apr 2018 09:31:48 +0200
> Johan Klokkhammer Helsing <johan.helsing at qt.io> wrote:
>
> > Some clients rely on the physical size to determine the physical DPI. With the
> > previous implementation, we would report 1px==1mm, which is a DPI of 25.4,
> > which is incredibly low.
> >
> > The problem is solved by setting a physical size so the DPI is close to 72
> > instead. If the output is scaled, the DPI is set to the corresponding multiple
> > of 72.
> >
> > This makes the headless backend more usable for automated testing of DPI
> > sensitive functionality such as point sized fonts.
> >
> > Signed-off-by: Johan Klokkhammer Helsing <johan.helsing at qt.io>
> > ---
> >  libweston/compositor-headless.c | 16 ++++++++++++----
> >  1 file changed, 12 insertions(+), 4 deletions(-)
>
> Hi,
>
> this is a good idea, but could you rebase this patch to master?
>
>
> Thanks,
> pq

Hi,

Would it make sense to change the protocol to allow compositors to send a zero
physical size in case it isn't relevant?

> >
> > diff --git a/libweston/compositor-headless.c b/libweston/compositor-headless.c
> > index 9307a36a..9f1a1a72 100644
> > --- a/libweston/compositor-headless.c
> > +++ b/libweston/compositor-headless.c
> > @@ -180,12 +180,19 @@ err_malloc:
> >  	return -1;
> >  }
> >
> > +static int
> > +physical_size_for_dpi(int pixels, int dpi)
> > +{
> > +	static const float mm_per_inch = 25.4;
> > +	return pixels * mm_per_inch / dpi;
> > +}
> > +
> >  static int
> >  headless_output_set_size(struct weston_output *base,
> >  			 int width, int height)
> >  {
> >  	struct headless_output *output = to_headless_output(base);
> > -	int output_width, output_height;
> > +	int output_width, output_height, output_dpi;
> >
> >  	/* We can only be called once. */
> >  	assert(!output->base.current_mode);
> > @@ -207,9 +214,10 @@ headless_output_set_size(struct weston_output *base,
> >  	output->base.make = "weston";
> >  	output->base.model = "headless";
> >
> > -	/* XXX: Calculate proper size. */
> > -	output->base.mm_width = width;
> > -	output->base.mm_height = height;
> > +	/* XXX: Make this configurable */
> > +	output_dpi = 72 * output->base.scale;
> > +	output->base.mm_width = physical_size_for_dpi(output_width, output_dpi);
> > +	output->base.mm_height = physical_size_for_dpi(output_height, output_dpi);
> >
> >  	output->base.start_repaint_loop = headless_output_start_repaint_loop;
> >  	output->base.repaint = headless_output_repaint;
>
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