video bleeds through somewhat between sessions

[Jordan Crouse]

On 01/08/08 15:00 -0400, Mikus Grinbergs wrote:
> 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.

Nothing to worry about - just a fun little side effect of video
acceleration.

Jordan

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