Paul Kienzle wrote:
> Hi all,
>
> I replaced one of the text_rotation examples with r'$\rm{mathtext_{225}}$'
> to see if rotation is supported for mathtext. It is not in the current
> trunk downloaded today.
It's only not supported in the bitmap (Agg and Gdk) backends. It works
fine in the vector backends.
> Before I look to deeply into this myself, is there anyone working on it
> already? Is there anything I need to look out for when implementing it?
I've made a few excursions down that road --
For bitmap font rendering, the entire math expression is first laid out
in a greyscale bitmap buffer, which is cached and then transferred to
the main plot bitmap. It was already that way when I got here, and I
assume that's an important optimization (so the text doesn't have to be
re-laid-out when the plot is zoomed/panned). I say "perhaps" because I
have no data to back it up, and don't know if that came out of profiling
or not.
There are a few key low level pieces that are missing for rotation:
- FT2Font.draw_glyph_to_bitmap does not support rotation. This would
have to be added, or there may be a way to use
set_text/draw_glyphs_to_bitmap which does support rotation. However,
that would make rendering the entire expression to a single buffer much
more difficult.
- The horizontal lines are all drawn as filled rectangles aligned to the
pixel grid, directly into the font buffers. That will probably have to
be pushed upward into the Agg layer to get good line drawing at
arbitrary angles -- but that also makes caching the bitmap a little more
difficult. So maybe it makes sense to implement our own Breshenham's
algorithm in ft2font.cpp.
All this will be affected by John's proposed refactoring of the
backends, of course, which has kind of kept me off of it in a "wait and
see" kind of mode. Right now, each backend has a custom interface to
communicate with mathtext -- whereas mathtext should simply be calling
the same low-level methods on all backends to get its job done. That,
of course, would make this buffer optimization harder (or at least it
would have to be thought about differently).
Let me know if you decide to implement this and let me know if you have
any questions about the code. Otherwise I'm happy to add it to my queue.
Cheers,
Mike
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