Re: Control fb problem on 8500

On Mon, 21 Aug 2000, Michel [iso-8859-1] Dänzer wrote:

Michael Schmitz wrote:

quoted

quoted

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That's what I was thinking about. However, I'm not sure that XFree
supports a display with discontiguous lines in video memory. I think I
read that somewhere in some mailing list or X doc... Can any of the
XFree specialists confirm?

I can speak for XFree86 3.x only, not for 4.x.

The only way to work with this is to make xres_virtual = xres+0x20. But
then XFree86 will draw into the cursor region, too.

I think it used to work without such a hack - some old m68k Macs had the
video scan lines start every 1024 bytes but the actual xres was smaller.
I'll have to look at the macfb code to see what xres_virtual was set to.
I'm sure the X server didn't draw to the offscreen region as that would
have caused a bus error (at least the earlier 3.3.x versions didn't.
Later X versions drawing beyond xres would in fact explain bus errors
some people saw ...).

X 4.0 distincts 3 values:

'xres'	- physical horizontal resolution of the current mode.

virtualX - horizontal resolution of the virtual screen. Never changes during a
screen's life.

displayWidth - the length in pixels of each scanline in memory.

I guess this doesn't change during the screen's life neither.

Unfortunately, the fbdev driver still assumes that displayWidth == virtualX,
and most other drivers have adapted that assumption (for most of them it's
right though :) .

Yuk, so we not only have depth/bits_per_pixel mixups but also
virtualX/displayWidth mixups :-(

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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


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