Re: [linux-fbdev] Is a FontCache worth implementing ?

[James S. <jsi...@li...>]

>I was wondering if it could be worthwhile (speedwise) to implement
>a fonctcache for fast character display.

If you think about it we already have something like that with teh current
system execpt instead of it being in card memory it is in system memory.
Using a image blitter you can translate that data from normal RAM to the
video card memory. The nice thing about a image blitter is you can do
depth translations (mono to depth X). I though about using a Glyhp
approach. The voodoo 3 card has a pattern buffer for up to 64 Glyphs which
can then be very quickly painted on the display. The problem is the
console system supports alot more characters than that. In the future I
hope even more.

>So I was wondering about a good ol' font cache : using regular
>fbcon_cfbXX_putc() in ofscreen memory once per character (on-
>demand, likely), and just _bmove() them to proper place.
>
>On the pm3, that would cost 4 memory access to the registers
>(in PCI memory space) (6 if not properly aligned, for the
>scissors stuff) plus the hardware copy, compared to whatever
>fbcon_cfbXX_putc() use.
>
>Would that be worth the hassle of adding the fontcache ?
>(I have no idea what putc() actually cost).
>
>Would that be worth adding a more generalized implemetation
>on top of existing _bmove() so that every hardware-accelerated
>board could use it ? (those without HW-accel putc(), that is)
>
>Is that already planned for the 2.5.x API ? (haven't seen
>anything to that extent in 'ruby' but I might have
>overlooked something)

Yes. This is the way the ruby tree handles it. I just got it working in
the ruby tree. The only problem is their is some bug in take_over_console
I have to chase down but I do have fbcon running using a voodoo 3 along
side my MDA. There are 3 functions. One is rectfill which does things like
clear the margins etc. Then their is fb_copyarea which copys a area of the
screen to another area of the screen. The last function is fb_imageblit
which transfers data from host memory to screen memory. This is used to
draw the penguin and text. Yes it is simpler to use the accel engine. A
good example is the new tdfx driver in the ruby CVS.

MS: (n) 1. A debilitating and surprisingly widespread affliction that
renders the sufferer barely able to perform the simplest task. 2. A disease.

James Simmons  [jsi...@li...]               ____/|
fbdev/console/gfx developer                             \ o.O|
http://www.linux-fbdev.org                               =(_)=
http://linuxgfx.sourceforge.net                            U
http://linuxconsole.sourceforge.net