todo

一个利用SDL语言来实现svgalib函数的示例程序

Should add options (possibly not default?) to make it possible to:

- convert 8-bit images to 24-bit;

- use the viewer mode for *everything* (assuming it's sane, i.e.
  640x480 or better, and 256 colours or better - temporarily resort to
  640x480 256 or 16-colour otherwise). This means the file selector
  and help page will need to also support 15, 16, 24, and 32-bit
  modes.

Without these changes zgv risks being a real pain to use on modern
monitors, some of which blank the screen not-so-briefly on mode
changes. Besides, I do like the idea of sticking to a single mode. So
I should probably make these the default, but be sure to add a
separate top-level "why is zgv slower now?" section to the info if I
do, explaining why, and how to disable it.


Various problems with SDL backend:

- run it on the console using svgalib as *its* backend :-), and exit
  the file selector's help page. Seems to briefly flash the screen
  blue. Not sure if this one is my fault or not, SDL's svgalib support
  does seem a bit cranky. [This one still happens despite my colour
  fixes for fillbox etc., so this one may be SDL's fault.]

- the SDL code assumes traditional PC encoding for 15/16/24/32-bit,
  and ignores any shift/mask info that SDL provides. This is likely to
  be ok on anything PC-based, but could break rather dramatically
  elsewhere.


Reread timeout and slideshow timeout are disabled for the current file
after a GIF is animated - this should be mentioned in the manual.


A `list modes available' option would be nice, and useful for
troubleshooting.


The TIFF reader could do with progress reporting. Unfortunately, the
TIFF format and libtiff combine to make this a total pain to do in a
sufficiently general manner without killing the loading speed. Maybe I
could try reading line-by-line with progress report, then resort to
no-progress read-at-once if it can't be read that way? Even for the
line-by-line case we have the not-abortable problem - but bearing in
mind that the hffunc would only be called at a well-defined time
outside of all libtiff functions, it should be possible to close
things down cleanly.


It would be nice if the smaller/bigger mode keys ([,]) worked in the
selector too. Could even use the same code to do it
(change_mode_size() in vgadisp.c) if hacked slightly (would need to
remove dependence on pixelsize, effectively 1 in the selector).


The (concept) indexing of Invoking zgv is weak at the moment -
everything's at the top of the node, when most of them should go next
to the thing they're indexing.


Recursive updates don't honour the fs-slow-thumbnail-update setting
across directories - that is, they jump to the first file which needs
changing. But frankly, this is a feature not a bug. :-)


I suspect the small italic font isn't being used any more; should
check, and get rid of it if so.


The file details dialog doesn't look so great if the old line-based
text is enabled. But I'm probably going to drop the line-based text
soon, so I doubt there's much point trying to fix this. :-)


readgif.c should cope with files with more than 256 images.
(Technically it does *cope* with more images, but it doesn't load
them.)


Dithering in 15/16-bit modes could probably be made faster, the
implementation is fairly basic at the moment.


If you specify selector colours (with the col-* options) which don't
differ by very much, and thumbnails are being displayed, then the
differences disappear entirely and only one of the close colours is
shown.


Should probably have right-button-menu options for GIF animation,
auto-mode-fit, and smaller/bigger mode.


It might be nice to have a further `act like xzgv' option for reversed
mouse movement in the viewer (dragging the picture around, rather
zgv's dragging the screen around). But probably tricky to get the feel
right, given the lack of a mouse cursor when doing it.


Copy over any handy build changes from xzgv. Most already dealt with,
but doc/Makefile hasn't been changed to use gzipped info files and
chmod a+r the dir file (important if install-info created one from
scratch, for example).


Mouse support isn't really finished - the goto-dir dialog should have
ok/cancel buttons, and currently you can't interrupt file loading and
thumbnail updates. The latter two would need a custom mouse event
handler temporarily installed, so that we could avoid losing any
clicks. Actually it might not be too bad an idea to always use a
custom handler; that would be easier. After all, on a slow machine you
can already lose clicks during a file-selector screen redraw!


File move should probably delete any existing thumbnail for the file
if the file itself is moved successfully.