video bleeds through somewhat between sessions

[Mikus Grinbergs]

>> G1G1, Joyride 2241.  In one Terminal session started mplayer -- it
>> was playing a movie.  Went to another Terminal session, and entered
>> some commands.  Noticed that not all of the text on that screen was
>> equally distinct - some of it was paler than others.  Noticed that
>> *which* text was paler changed from second to second.  Realized that
>> the paler text in the second Terminal screen corresponded to the
>> *brightest* areas of the movie frame then being shown in the first
>> Terminal screen (the one I had switched way from).
> 
> Video is muxed to the visible screen through the use of a color key -
> given a rectangle of some size, the hardware compares all of the pixels
> in that rectangle against a set color - if they match, then a pixel of
> the video frame is shown, otherwise not.
> 
> The color is specified by the video application - most applications use
> very saturated colors similar to those used in "green" or "blue" screens.
> My favorite is hot pink (0xFF00FF).  IIRC, mplayer uses an off-shade color
> of grey, so it is easier to run into the possibility that other applications
> will match the color key, especially with automatic shading such as
> anti-aliasing.

I did NOT understand at all what you are trying to say.  [I used the
words in the subject line to try to describe that what *would* have
been shown by one program (whose output "window" I was NOT looking
at) "bled through" to affect what *was* being shown from ANOTHER
program (whose output "window" I WAS looking at).]


In my mind, a 'session' can request that certain pixels be displayed
on the screen.  [If a text-output program is running, it will
request pixels which make up an image of a text character.  If a
video-output program is running, it might request pixels which make
up an image of a white cloud.]  My point is that each program (that
is, 'session') supplies __its own__ set of rendering requests.  I
would expect that if I am looking at an area of the display which I
thought was dedicated to output from program A, then I will  ONLY
see pixels as requested by program A (no muxing!).

What was happening to me was:  while looking at the screen showing
output from program A (Terminal 'session'), the pixels themselves
(i.e., for black text characters) appeared to have been requested by
program A.  But the intensity of those pixels (how black they were)
appeared to be MODIFIED by whatever intensity program B (mplayer
'session') wanted for that spot on the screen.  Since it is the
driver interface (or something) software that ACCEPTS the
pixel-rendering requests issued by the running programs, I would
expect that when I switch away from session B, the rendering
requests still bing issued by session B would be IGNORED in their
entirety (until B again has the "focus").


Why should the video have to be 'muxed' from the simultaneous output
of multiple sessions ?  Why, when session A has the "focus", should
anything done by session B affect  HOW  A's output gets shown ?

mikus