[cairo] Zero matrix transformation
d at domob.eu
Thu Mar 20 00:18:45 PDT 2008
Jeff Muizelaar wrote:
> On Wed, Mar 19, 2008 at 12:22:10PM +0000, Daniel Kraft wrote:
>> I just set-up git cairo and pixman and was playing around a bit with it.
>> On the GSoC ideas page there's one item:
>> Fix cairo so that a degenerate matrix draws nothing rather than
>> triggering an error state. That is: cairo_scale (cr, 0, 0); should not
>> cause an error, (though maybe it shouldn't actually draw nothing for
>> painting an infinite source pattern---compute the average color for a
>> surface-based source pattern perhaps?).
>> I tried to reproduce this, but for me (using the hello-program from the
>> FAQ with this scale-statement added) this seems to work. Using numbers
>> between 0 and 1, the writing becomes smaller as I would expect; for
>> using 0, nothing is drawn, as the item states as desired behaviour.
>> Did I understand something wrong, did my test not trigger the error for
>> some reason, is this already done...? I'd like to start working on
>> cairo a bit to make experiences, and this looked not too hard. If you
>> have any other suggestions, I'd be happy to hear from you!
> In your example, if you call cairo_status(cr) after the call to
> cairo_scale(cr, 0, 0) you should get CAIRO_STATUS_INVALID_MATRIX.
> Alternatively, you can try changing the scale back to 1, 1 with
> cairo_set_matrix after setting it to 0, 0 and you should not be able to
> draw anything.
> The desired behaviour is that nothing be drawn only when the matrix is
> degenerate. If it becomes well-formed drawing should work as normal
> instead of the cairo context remaining in an error state.
Ok, thank you! I'm a few days off now, but after that I'll try it out
and hopefully also be able to help here.
Done: Bar-Sam-Val-Wiz, Dwa-Elf-Hum-Orc, Cha-Law, Fem-Mal
To go: Arc-Cav-Hea-Kni-Mon-Pri-Rog-Tou
More information about the cairo