Re: [Linux-fbdev-devel] fb_imageblit semantic

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

On 17 Mar 2003, Antonino Daplas wrote:
> On Mon, 2003-03-17 at 18:40, Petr Vandrovec wrote:
> > On 17 Mar 03 at 11:31, Geert Uytterhoeven wrote:
> > > On 17 Mar 2003, Antonino Daplas wrote:
> > > > As Geert said, it's not just trivial, but logical to split fb_imageblit
> > > > into two.
> > > 
> > > So, are we gonna split it? This will also make hardware acceleration support
> > > more clean. E.g. most sbus drivers do color expansion in hardware, and fall
> > > back to cfb_imageblit() for the logo.
> 
> It's up to James, though I vote for it.  And I don't think any driver
> has accelerated versions of fb_imageblit for the logo, since any
> performance gained is probably minimal and it will involve too much work
> for something that's going to be done only once.

Wait until someone wants 256-color fonts ;-)

> > > > > OK, so rule is that if depth=0, input is 1bpp with palette in bgcol/fgcol,
> > > > > while if depth != 0, then palette is in info->pseudo_palette ?
> > > > 
> > > > Yes.  You can also say that if image->depth != var->bits_per_pixel, do
> > > > color expansion or reduction, whatever the case may be.
> > > 
> > > Hmmm... Note that image->depth can be larger than 8, while the image data is
> > > still 8-bit. This is an inconsistency.
> 
> I was thinking that if image->depth=8 and var->bits_per_pixel=4, then
> the driver is in danger of going out of bounds when referring to the
> pseudo_palette.  But I forgot that the fb_show_logo() takes care of
> avoiding that :-)  And yes, current usage of image->depth is pretty
> inconsistent and basically useless.
> 
> > image->depth for logo must change to 8. Or remove depth completely after
> > splitting imageblit to paintchar & paintlogo, as currently depth is
> > useless anyway: target format is defined by framebuffer layout, not
> > by image->depth, and source format is hardwired to the code.
> 
> You're correct.  If it's going to be split, image->depth becomes
> redundant.

That depends... How do we draw the monochrome penguin? Using image->depth is 1
or 8? The latter (current method) is slower, since we need to expand the
monochrome logo to 8-bit first, and (usually) compress it to 1-bit in the fbdev
driver afterwards.

And perhaps we may want to draw 32-bit ARGB images later?

So I see the following possible valid values for image->depth:
  - 8 (logo with up to 256 colors and LUT)
  - optional 1 (monochrome logo, if we don't want to expand?)
  - optional 32 (ARGB image, dithering left to the driver?)

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