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

[Geert U. <ge...@li...>]

On Sat, 10 Mar 2001, James Simmons wrote:
> True. You could do this for cards that have the avaliable memory. If fbcon
> is running at a resolution that occupies the entire memory then you are in
> trouble. You can do many fancy tricks. I leave it up to the driver writer
> to be fancy. The goal is to draw some image. Keep in mind I wanted to also
> want to have the function draw the penguin. It is very miss leading the
> name of the function. It should be drawimage instead. Also for cards that
> lack this function a software emulated drawimage has to be done. Could
> people post all the possible ways a "fontcache" could work. I see
> imagedraw is going to the touchy one.
> 
> >What about pattern fills ? Where you provide a bitmap, and the accel
> >engine copies this bitmap, putting 1 color for the 1s and another (or
> >transparent) for 0s.
> 
> Same thing. The goal of the function is to draw some image. How it is
> implemented is up to the driver. Another way to do it is make textures of
> fonts and using texture mapping to draw the characters. I seen something
> like this used for a X server before. The windowing was done with the z
> buffer which was used to act like hardware window IDs. Each window then
> was textured mapped with whatever the program was trying to display. The
> texture map changed when needed. X term wa steh trickiest. Alot of little
> texture maps but it still was fast.

With a font cache you store all fonts in an off-screen area of graphics memory,
and let the graphics acceleration engine do monochrome-to-color expansion for
each individual character.

For systems that don't have hardware acceleration for monochrome-to-color
expansion and that have bitplanes (the Amiga comes to mind :-), it's much
faster to not draw individual characters at the monochrome-to-color expansion
level, but to prepare a bitmap for a bunch of characters and let that expand by
software (using 32-bit accesses instead of 8-bit accesses for individual
characters).

So here we have a trade-off: do we want to draw individual character bitmaps
(possibly hardware accelerated), or do we glue individual characters together
and draw the composite bitmap?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@li...

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds