On 2009-10-25 15:11-0500 Hezekiah M. Carty wrote:
> On Sun, Oct 25, 2009 at 12:34 PM, Alan W. Irwin
> <irwin@...> wrote:
>> Hi Hazen:
>> If you look at the results from ext-cairo-test, the current background is
>> white. I followed up that issue, and our default cmap0 file is being read
>> correctly which includes a black background. However, that black PLplot
>> background is currently being ignored (and I presume we are getting a
>> default white background from the cairo libraries instead) because there is
>> no handling of background colour for the extcairo device in cairo.c.
>> Would you be willing to add background colour handling to extcairo like you
>> do for all other cairo devices?
> It is my understanding that automatically clearing the page to the
> background color is intentionally left out of the extcairo device
> intentionally so that the provided context is preserved. This way a
> user can provide, for example, an image they want to plot over and it
> will be preserved.
> I use this feature of the driver quite often, so I would prefer that
> the extcairo functionality remain as-is, at least in the default case.
There are two issues here. (1) Should we allow specifying a possibly
transparent background colour for extcairo similar to every other device
driver? (2) If the answer to (1) is yes, should that default background
I would argue pretty strongly for (1) simply because most/all of our devices
have background colour setting capability, and I assume some extcairo users
will want this as well (e.g., for our ext-cairo-test case). I think the
answer to (2) should depend on what the majority of users are doing with
extcairo. I don't have a clue about that usage, but if you think the
majority will be using background images instead of solid backgrounds, then
I would be willing to go along with making the background transparent by
default for the extcairo case simply as a matter of convenience for that
majority use case.
Alan W. Irwin
Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).
Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project