[Cairo] Re: [xsvg] cairo_text_extents ?
spitzak at d2.com
Tue Dec 30 10:19:22 PST 2003
On Wednesday 17 December 2003 07:34 pm, Carl Worth wrote:
> It occurred to me that I didn't know for sure how cairo used the CTM
> and font matrix when dealing with relative placement within
> cairo_show_text. So, I wrote a little program to find out. It's in CVS
> at cairo-demo/png/text-rotate.c. The resulting image can be seen at:
This image shows how I expected it works. Certainly this makes sense and is
simple to describe. My concern is that the interface, as designed now,
provides a y_advance value that any program calling it must be prepared for
this to be non-zero. Also the fact that currently no fonts are producing
non-zero for both x_advance and y_advance means that calling programs are
unprepared for this case. I would greatly prefer if the y_advance was
eliminated so that calling programs know this case cannot happen.
My initial idea was to simply eliminate one number from the font matrix so
that rotations were impossible, only scale, skew, and translate. Vertical
text would be selected much like it is now (by another flag to the font) but
would produce "sideways" letters so that the x_advance could still contain
After reading some of the feedback I came up with this idea where rotations
are allowed and the rotation is then used to select vertical layout.
It is quite possible that my idea is a big waste of time and only horizontal
and vertical layout would ever be selected, diagonal may require too much
control over individual glyph positions.
Perhaps my original proposal where selecting a vertical font produced the
sideways letters would be easier to do. Another possibility is to just
document the fact that at no time will x_advance and y_advance both be
non-zero and that which one is non-zero is the same for all glyphs in a font.
This could also be enforced by putting the advances into the same field and
having some other indicator as to whether the font is horizontal or vertical.
,~,~,~,~ ~ ~ ~ ~
/\_ _|_========___ Bill Spitzak
~~~/\/\\~~~~~~\____________/~~~~~~~~ spitzak at d2.com
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