Re: [Linux-fbdev-devel] clipping

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

On Sat, 2003-01-11 at 03:39, James Simmons wrote:
> 
> > > I thought about this. Originally I did have this function but removed it.
> > > WHat do you think Geert?
> > 
> > Yes, that's OK.
> > 
> > But I was most concerned about fb_ops.fb_imageblit(), since clipping impacts
> > fb_image.data as well. IIRC, all (most?) current clipping implementations
> > modify fb_image.{dx,dy,width,height} only, without updating fb_image.data.
> 
> Good point. Of course we could ignore pieces of data in that image instead 
> of altering the data. Altering the entire data would be expensive.
> 
> > > > 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.
> > 
> > Well, in between the calls to fb_ops.fb_check_var() and fb_ops.set_par() you
> > can still perform that check. But it's indeed ugly.
> 
> Altering to the framebuffer via /dev/fb that would effect the tty should 
> not remain after the final close of /dev/fb. Instead the console should 
> reset to its previous state before we first opened /dev/fb.
> 

Right :-) I believe this is nearer the correct solution.  Clipping is
typically used to maximize graphics/video bandwidth, but fbcon is using
it to "cover up" possible bugs in the code.

If we can have a correctly working fbcon, without the clipping code, it
will be proof to its robustness.

So, basically, on the first open we save xres, yres, xres_virtual,
yres_virtual and bits_per_pixel, and restore them on the last close, is
this correct?  Any other parameters that will affect the actual and
virtual window size?

Tony