Re: [Linux-fbdev-devel] clipping

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

On 10 Jan 2003, Antonino Daplas wrote:
> On Fri, 2003-01-10 at 05:24, James Simmons wrote:
> > > So perhaps, a function something like this:
> > > 
> > > void fb_clip(struct fb_fillrect *region, struct fb_fillrect *clip);
> > > 
> > > This should not be difficult to implement, and I'll code it if everyone
> > > agrees.
> >  
> > I thought about this. Originally I did have this function but removed it.
> > WHat do you think Geert?
> > 
> > > The other option (which I don't like) is just to check the passed
> > > fb_var_screeninfo in the put_var ioctl against the current console
> > > window size.  But this is not foolproof as we will not be sure of the
> > > resulting window size _after_ the fb_set_var() call.
> > 
> > Yuck!!! The other way is better.
> > 
> 
> Yes, I thought so too :-).
> 
> I think one scenario why we need clipping is changing bits_per_pixel,
> ie, changing from 8->16 will drop your vyres by half and it's difficult
> to determine this unless you do another check before the set_par(), as
> Geert mentioned.  Worse still, there is little if no valid memory past
> vyres but the console thinks there is.  That's where you will get a
> segfault.
> 
> Whereas explicitly doing fbset -vyres 768 will not cause a segfault,
> because you still have valid framebuffer memory past y=768.

That depends. On unified memory architectures or if the graphics memory is
shared by two heads, you may still corrupt someone's memory.

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