[Konsole-devel] [Bug 172250] Vim in Konsole is slow

[Robert Knight]

http://bugs.kde.org/show_bug.cgi?id=172250





--- Comment #10 from Robert Knight <robertknight gmail com>  2008-10-23 15:45:53 ---
> Geforce GT8800, nvidia-drivers-177.80 (x86-64)

Historically NVidia's drivers have been very slow with KDE 4, slower than
running the application through a driver (like nv or vesa) with no acceleration
at all.  I was under the impression that this is fixed with the latest drivers
though.

> Are you using sprites of letters that get bitblt into
> the NxM raster of the terminal screen ? 

Text is divided into chunks of equally formatted characters and then dispatched
to Qt to draw.  Layout of the text and conversion to a series of glyphs to blit
to the screen is handled by Qt - the exact path taken will depend on the
platform and the current graphics engine.  gnome-terminal and Konsole 3 work
the same way.  Konsole 4 is theoretically better because Konsole 3 dispatched
characters to Qt one at a time for drawing whereas Konsole 4 sends text in
batches divided up according to character formatting.

The reason for not just storing one pixmap per ASCII character and then
blitting that to the screen in the appropriate place is because Qt's text
drawing provides comprehensive unicode support, anti-aliased glyphs and
sub-pixel rendering - or in short, pretty text and funny languages.  Of course,
if you don't care about either of these then you're incurring overhead for
something that is not being used - although the text engine in Qt should try to
minimize the overhead in cases where you're drawing un-smoothed ASCII
fixed-width text anyway.  On my Intel hardware and even my very old Radeon M6
Konsole 4 is faster than Konsole 3 - mainly because of the above change in how
characters are dispatched for drawing. 


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