Re: [Linux-fbdev-devel] Some questions

[Thomas W. <th...@wi...>]

Antonino Daplas wrote:
> On Fri, 2003-03-07 at 23:19, Thomas Winischhofer wrote:
> 
>>This works - perfectly, I must say.
>>
>>However, the scrolling problem is still here, but I think I know the 
>>reason for this:
>>
>>Imagine a console of 120x40 (using the std 8x16 font), on a screen of 
>>1024x768, using ypanning.
>>
>>This uses only 40*16=640 pixels vertically instead of the 768 available.
>>
>>The problem is the y panning, and is kind of both console's as well as 
>>the driver's fault:
>>
>>When the y panning area reaches its end, it's supposed to copy the 
>>screen to the beginning of this area and pan to position 0.
>>
>>However, fbcon calculates p->vrows by info->var.yres_virtual / fontheight.
>>
>>This disregards the fact that the visible screen area is actually larger 
>>than the area console is supposed to use.
> 
> 
> I've tested where the virtual window size is much smaller than the
> physical dimensions, and I do see the glitch you mentioned.  But it's
> mainly due to clear_margins().  clear_margins always erases a constant
> amount (physical_height - actual height).  So if you happen to pan just
> enough that there's not enough screen estate left, it will attempt to
> clear past yres_virtual.  Bad for drivers that do not implement
> clipping. Perhaps, block moves are involved here also, I'm not sure. 

1) Sisfb does no clipping, but there is plenty of video RAM past the 
virtual area.

2) I don't think we are talking about the same thing. Clear_margins() 
(which I haven't looked at, I confess) assumingly ... erm.. clears the 
margins. But why is it involved in scrolling any panning?

> So your patch has the correct idea, but here's a simpler one. It just
> reserves enough screen estate equal to difference of physical height and
> virtual height. I've tested this even using stty cols 2, and it works
> okay.

I don't see why this is simpler, but I do see it wastes a lot of screen 
space :)

BTW:

  	p->vrows = info->var.yres_virtual / vc->vc_font.height;
+	p->vrows -= info->var.yres - vc->vc_rows;

Look:

rows =          40
yres =         768
yres_v =      2048
font height =   16

vrows = 2048 / 16 = 128  (character unit)

128 - (768 - 40)

is negative...

Personally, I'd go with my first patch from earlier today. I tested this 
intensively in the meantime, and it Simpy Works(tm).

> NOTE:  Since we need var->yres, this time, we need to refer to info->var
> instead of the adjusted var.
> 
> BTW:  I've tested moving clear_margins before panning, it still doesn't
> remove the onrushing text past the virtual window height.  This would
> seem to need clipping to remove that eyesore.  

Honestly, I don't consider this important... But I thought you'd simply 
exchange the order of calling pan_var and drawing the characters... 
(which IMHO would be the correct order, logically speaking)

Thomas

-- 
Thomas Winischhofer
Vienna/Austria
mailto:th...@wi...          *** http://www.winischhofer.net