[mcclim-devel] text with negative x-offsets

[Christophe Rhodes]

[ to the real mcclim-devel address, this time ]

Hi,

Find attached a preliminary patch to deal with the fact that, in
general, glyphs from fonts are not constrained to draw only to the
right of the cursor position.

This patch does not correct any of the assumptions about horizontal
left-to-right rendering or single-line rendering.  However, it
attempts to cater for all cases which are currently functional, for
the CLX backend (both with ordinary X fonts and with the experimental
Freetype bindings).  It is probably fairly tricky to trigger problems
without this patch using the ordinary X fonts, but using the Bitstream
Vera family of fonts in climacs for a little while tends to degrade
the display as incremental-redisplay fails to erase the entirety of
glyphs (because the bounding rectangle is wrong).

It works by introducing a new internal function,
TEXT-BOUNDING-RECTANGLE*, which is somewhat analogous to TEXT-SIZE and
STREAM-STRING-WIDTH, only capable of dealing with non-zero offsets.
TEXT-BOUNDING-RECTANGLE* returns the coordinates of a bounding
rectangle that would bound the output of DRAW-TEXT* at position 0 0
and with :ALIGN-X and ALIGN-Y taking their default values.  It is
entirely possible that I have miscalculated some of the other cases in
DEF-GRECORDING DRAW-TEXT: caveat user.

With this patch, I was no longer able to trigger disastrous redraw
effects on simple climacs editing operations; previously, entering 
"     ___" on a line, putting point at the start of the line and
then hitting the space bar a few times would leave a trail of pixels
as the output records for almost all the text would move (on my
display here, with my freetype options, the #\_ character has an
active pixel at -1).

The real test case for this is the tablature editor, which is using a
font designed such that the centres of characters are at (0,0);
unfortunately, I'm not in a position to run it right now, but with
luck we'll be able to test this tomorrow (and extend this work to the
Postscript backend: maintainers of other backends should chime in at
this point to indicate whether this solution is acceptable and
implementable :-).

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Cheers,

Christophe