Re: Pango tab stops

[Behdad Esfahbod <behdad behdad org>]

On 04/01/2009 07:27 PM, Ian Puleston wrote:
> Hi,

Hi Ian,


> I want to use a PangoTabArray to pass tab stop settings to a print function
> along with text to be sent to a printer. The idea is that the caller passes
> the pre-set PangoTabArray, and the print function then calls
> pango_layout_set_tabs to add it to the PangoLayout created via
> gtk_print_context_create_pango_layout.
>
> But there seems to be a problem with setting the tabs correctly for the
> resolution (dpi) of the printer. With a PangoTabArray the tabs are specified
> in either pixels or Pango units, and to use either to set tag stops at fixed
> distances requires knowledge of the resolution of the device, but the code
> requesting the print cannot know that (the user has not even selected a
> printer yet).

No it doesn't.  The cairo PS/PDF/SVG surfaces use Postscript points as their 
device "pixel".  That is, for positioning purposes, 72dpi is all you care 
about.  The actual resolution of the printer printing them is irrelevant.

Makes sense?

behdad


> Two solutions that I can see are 1) define the API to accept tabs set for a
> 300 dpi printer and have it internally multiple them up or down if necessary
> once the print device has been selected, or 2) pass the tab settings in a
> generic array or list and create the PangoTabArray internally once the print
> device has been selected.
>
> Neither is particularly neat, so I'm wondering if there may be some existing
> structure or API somewhere in GTK or the other components for passing tab
> stops in units such as inches, mm, etc.?
>
> Ian
>
>
>
>
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