[mcclim-devel] questions on text graphics

[Jack Unrue]

I've been working on graphics support in my backend code and
have a couple questions.

What are the intended side effects of the TEXT-STYLE-*** methods, if
any? Are they solely intended to answer "what-if" questions, e.g.,
"what would the ascent be if the font was :fixed and :bold ?" Or are they
also meant to update the medium's text style attributes, as I see the
gtkairo backend doing? Since one can add :before/:after methods
on (SETF MEDIUM-TEXT-STYLE) to synchronize the underlying
graphics context -- and presumably such a style attribute update
necessitates repainting -- is that sufficient or should I really be
planning on synchronizing attributes anywhere that styles are passed
as arguments?

MEDIUM-DRAW-TEXT* appears to be called for each character in the
string to be rendered. I gather that a backend is expected to be able
to buffer such operations (see next question). But from looking at
backtraces, the cause seems to be CL:WRITE-STRING processing the
output stream one char at a time. I'm running on CLISP, so perhaps you
lucky SBCL folks have your string output processed in batches. I take it that
the use of WRITE-STRING is a consequence of CLIM's stream output model?

More generally regarding output buffering, I see the MEDIUM-FINISH-OUTPUT
and MEDIUM-FORCE-OUTPUT methods and can easily imagine how my
backend code might implement those. I also notice the public
WITH-OUTPUT-BUFFERED macro and that it communicates with the
backend by way of MEDIUM-OUTPUT-BUFFERING-P. Based on what
I'm seeing so far just with text output, I'm sort of inclined to implement
double-buffering unconditionally. Is that a bad idea, or am I missing a
level of abstraction between McCLIM's idea of buffering and my backend's
idea of buffering?

Thanks.

-- 
Jack Unrue