video bleeds through somewhat between sessions

Jordan Crouse jordan.crouse at
Mon Aug 4 11:05:43 EDT 2008

On 02/08/08 18:53 -0400, Mikus Grinbergs wrote:
> > It is the video chip's feature that it can display a video overlay over
> > the RGB bitmap. The pixels where the overlay can be seen is defined by a
> > colorkey (what was 0xFF00FF in the example), or the alpha component of
> > the display RGB bitmap (not used on the XO since the change 16 bit
> > bitmaps). What you are seeing that the X server does not disable the
> > video overlay while switching programs. It can be an error or just some
> > braindamaged X stuff. Either way, it has nothing to do with bitmap
> > operations.
> Then I believe there *was* something wrong:  When I was looking at 
> the "character-based" Terminal screen, there should not have been a 
> 'video overlay' interacting with what was being shown to me.
> When I am looking at the (full-screen) video output, if what I see 
> involves a 'video overlay' -- that's fine with me.  But when I 
> "switch away" from the 'session' displaying the video output, I 
> don't want "interference" to what I'm currently looking at (whether 
> that interference comes from a 'video overlay', or from whatever).

Then the video application needs to stop the video or change the
demensions of the overlay window.  The hardware is only doing what
it is told to do.

> --------
> Both persons who have answered me have talked about "how things from 
> the video frame can be seen".  But I was not looking at video - I 
> was looking at TEXT.  If I understand correctly what has been told 
> me here, neither the 'black' of the text characters themselves, nor 
> the 'white' of the background for the text, should have _allowed_ 
> "things from the video frame to be seen".  I definitely did not see 
> any color.  What I did see was that some parts of the 'black' text 
> characters changed briefly to _less_ 'black' (they went black <--> 
> gray <--> black) depending on where on *its* screen the ongoing 
> video 'session' WOULD HAVE depicted "bright" or "dark" areas.

Right - you were looking at text, which is not actually black and white
in sugar - it is antialiased (
The font renderer is antialiasing the text, so that there are numerous
shades of grey pixels surrounding the glyphs.  These will match the 
color key, and will refelect the video behind it, but since you are only
seeing a few pixels surrounding the text, there isn't enough context
to "see" the video from behind, but there is enough contrast for your
eye to notice the difference.


Jordan Crouse
Systems Software Development Engineer 
Advanced Micro Devices, Inc.

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