[cairo] API Shakeup: default matrix

Carl Worth cworth at cworth.org
Mon Apr 4 06:56:42 PDT 2005

On Thu, 31 Mar 2005 14:13:18 -0500, Carl Worth wrote:
> It occurs to me that there's a simpler approach here. We can simply
> say that the default CTM is always an identity matrix. Then, the PDF
> and PS surface types can be documented to have a device-size unit of
> one PostScript point (1/72 inch). That's definitely correct for those
> surface types, and it lets us avoid having to have the notion of
> "display" and "print" devices.
> As usual, I'll commit this soon unless there are any objections.

I've committed this now.

And now that we've got the notion of each backend documenting its own
size of device-space units, I wonder if all surface constructors
shouldn't just accept a size in device-space units. That's what we
have for image and display surfaces already.

This would mean changing the units for the size parameters for the
PS/PDF constructors from inches to points. I'd already been
considering switching from inches to a metric unit, (though I wasn't
sure about what scale to use cm? mm?). Just sticking to points would
allow us to avoid creating an arbitrary preference for any particular
paper size convention. And it might just be easier to remember, (since
everyone knows that PS uses points as its native unit).


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