Re: [Linux-fbdev-devel] fonts

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

On 22 Jan 2003, Antonino Daplas wrote:
> On Wed, 2003-01-22 at 00:14, Geert Uytterhoeven wrote:
> > On Wed, 15 Jan 2003, James Simmons wrote:
> > > > > The cfb_imageblit() function exhibited the same behavior.  I think we
> > > > > both made the wrong assumption that all monochrome bitmaps are packed. I
> > > > > think the rule is:
> > > > > 
> > > > >     The first pixel on the next scanline is always at the next byte from
> > > > >     the last pixel of the current scanline.  
> > > > > 
> > > > > So a 12x22 font has 16 bits per scanline but only 12 are usable, and the
> > > > > last 4 are used as padding.  It's worse with a 4x6 fonts where the
> > > > > 4-bits are just duplicated in the other nibble.
> > > > 
> > > > Yes.
> > > 
> > > All the font data should be packed and byte padded at the end of each 
> > > scanline worth of data. Also most accel engines expect the data to byte 
> > > packed.
> > 
> > What do you mean with `each scanline worth of data'? Data for one character, or
> > data for the whole font (i.e. all characters)?
> 
> I meant for each row of bits representing a pixel in a bitmap, the start
> index and the size of each row will be byte-aligned.  So, the padded
> version.

  [...]

> The latter is very difficult to support by most common hardware as they
> require the padding.  Actually, some, maybe most, cards require more
> than a byte padding. 

  [...]

> If we do need to support both versions, then we need extra fields to
> fb_image, such as clipx1 and clipx2, where: 
> 
> 	image.clipx1 = starting index;
> 	image.clipx2 = clipx1 + width;
> 
> (Do we also need something similar for the y coordinate?)

Or add sx and sy, cfr fb_copyarea. Makes clipping behave the same for both.

> I think I'll let you and James decide on this :-) 

I'm happy with the current scheme. I just wanted to be 100% what James meant
with `All the font data should be packed and byte padded at the end of each 
scanline worth of data.'.

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