From: <postmaster_at_diffenbach.org>
Date: Sat, 24 Jun 2006 02:30:44 -0400

A patch to optimize apps/gui/list.c, function gui_list_draw.

Previously, all lists were always redrawn in their entirety. With this
patch, when the list's start position (the item at the top of the
list) hasn't changed, only the /lines/ changed are updated. In almost
all cases, that means only two lines are updated, the line the cursor
is leaving and the line to cursor is moving to. When a list's start
position changes, or when a new list is shown, the whole list is
re-drawn using the original cvs code.

Provision is made to handle the "pointer" cursor as well as the
standard inverted bar cursor.

The speed increase depends on the font used; the smaller the font, the
more lines have to be drawn to fill the screen, and so the greater the
speed savings. Here's a non-controlled sample of the average speeds of
the regular and the optimized list redrawing, in microseconds, for
several font sizes, on my Ipod Video (G5, 60GB, using only 32MB of
memory, that is, build 15):


Font Height Average Unoptimized Average Optimized Ratio of
Unoptimized/Optimized
  5 123039.71 4555.51 27.01
  7 128322.65 15404.24 8.33
14 116112.13 7363.98 15.77
16 128704.18 8046.00 16.00
24 130604.73 20603.50 6.34

For ipods, there's an often mentioned problem of music play stopping
when lists are scrolled. This will not fix the problem, but will
alleviate it quite a bit.

Please perform the following experiment before using this patch in
build. Using your current build, play a song, then go to the menu and
rapidly scroll up and down the list until the music stops playing.
Then try the same using a build with this patch. Then do a logfdump
(Menu|Info|Debug|logfdump), and mail the file logf.txt in your
device's .rockbox directory to:
gui_list_opt AT diffenbach.org

Note that a peculiarity of tagcache makes this a bit more complex than
it would otherwise be; tagcache uses the same gui_list structure for
ALL its lists.


The patch can be found on the patch tracker, here:
http://www.rockbox.org/tracker/task/5591

Thanks.
Received on 2006-06-24