Re: [Linux-fbdev-users] [PATCH] cfbimgblt: Allow generic BitBLT functions to work with swapped pixel order in bytes.

[Antonino A. D. <ad...@gm...>]

On Fri, 2007-08-31 at 03:29 +0200, Pavel Pisa wrote:
> Hello Antonino,
> 

> The notice has been about rectangle fill and copy, which are in different
> files. I am not sure if they are used for console such way that it would
> could mean problems. The screen scroll should not be problem with
> swapped pixels in bytes. Any operation on whole lines should not be problem

fillrect is used by the vt layer to erase characters and by fbcon to
clear the screen margins in case the display width is greater than the
font width * screen columns.

copyarea, on the other hand, is used by the vt layer to insert or delete
a character, or by fbcon to scroll the screen if the scrolling mode is
SCROLL_MOVE.

> too. Only problem is if they are used for real moves with odd/unaligned
> X coordinates.

If you use non-8x16 fonts, it's indeed possible to have an X coordinate
which is unaligned. Example, erase the 2nd 7x14 character using
fillrect.  At 4 bpp, the origin of the 2nd character is at the 28th bit.

>  May it be - this would make some not so nice effects
> for cursor when some strange font width is used.
> 

You basically have 3 choices:

1. Fix copyarea/fillrect
2. Accept that the console may become corrupted if a non-8x16 font is
loaded.
3. Tell the console layer that it can only handle multiple-of-8 wide
fonts

Tony