Re: [Linux-fbdev-devel] clipping

[Antonino D. <ad...@po...>]

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.

Tony