[linux-dvb] Re: Need help understanding OSD ioctls, mostly SetColor and SetBlock.

[Ralph Metzler <rjkm@convergence.de>]

Chris Worley writes:
 > That solution would be okay if I could overlay graphics atop the 
 > video, and have alpha blending.
 > 
 > I could go without alpha blending, but graphics overlay atop the video 
 > is necessary, and it's not always nice rectangles.
 > 
 > If I draw the video from the DVB card into the video cards 
 > framebuffer, would I be able to overlay graphics on top (without 
 > getting into a race with the DVB card, which would overwrite my graphics)?
 > 
 > Maybe chromakey or colorkey?  For example, If I could draw black 
 > pixels onto the areas where I didn't want video, using the OSD 
 > routines, setting the blend to 0xf0, then have the DVB card draw into 
 > the video cards framebuffer memory, might I be able to get it to skip 
 > drawing regions of the frame buffer where I wanted to draw graphics? 
 > That idea wouldn't work; it would just draw my black pixels into my 
 > framebuffer, and it would overwrite any graphics drawn into the same 
 > framebuffer area.  Maybe a video card with z-order capability?
 > 
 > How do you do this?


Most VGA chips support hardware overlay including alpha blending.
This is supported in DirectFB.
See http://www.directfb.org/news/martin/window_demo.png,
http://www.directfb.org/news/martin/mhp_penguin_demo.png
or http://www.directfb.org/news/count/videoshot.png.
All show graphics with a live TV screen.

Just the video overlay could also be done with the video extensions 
of XFree but DirectFB is more optimized for speed and memory and
has other features needed on set-top-boxes.


Ralph






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