[vdr] Re: ANNOUNCE: Softdevice plugin. Use /dev/fb for output

[Holger Waechtler <holger@convergence.de>]

Roland Praml wrote:
> Hi,
> i need some tips in developing my plugin.
>
>
> > > > You need:
> > > > A VDR of course.
> > > > A strong CPU (i think 800 MHz+)
> > > Really 800 MHz+ ? DVDs can be played with a Celeron500 (without
> > > post-processing), so you should tune your plugin a little bit.
> > >
> > > Rene
> > When directly rendering to the framebuffer you can't use the graphics
> > card for scaling and YUV conversion, this wastes a significant amount of
> > time. Use DirectFB, SDL, XV, XRender, OpenGL or any other accelerating
> > graphics library of your choice.
>
> that's my problem, the plugin gets too slow if I implement all in software.
> I played around with the Vidix driver the last days. The YUV->RGB conversion
> and scaling is now accellerated by hardware (the decoding needs only 20-30%
> CPU time instead 50%-60% if the conversion is done by software)
>
> My dream is an implementation like this:
>
> MPEG2 -> [SW-Decoder] -> [HW YUV->RGB + Scaler] -> [HW-Alpha] -> Monitor/TV
> OSD   -> [SW-Renderer] --------------------------------^
>
> BUT:On my Matrox G200 I didn't figured out, how to display something BEFORE
> the BES-layer. (google think's that this is not possible)
It's possible, we're did things like this in the 
convergence-inhouse-software based on DirectFB. The trick is that these 
cards need actually a destination colorkeying/blending and not a source 
colorkeying like you are used to.


> If this is really not possible, how should I display OSD:
> - implement all in software (slow!)
> - scale the OSD in Software and blend with the YUV-Image (poor quality)
> - use another VGA-Card (e.g. Geforce4 MX)
Basically you have the freedom of choice when using modern graphics cards.

First you can do it using alpha-blended stretchblits. All modern 
graphics cards can do this in hardware and you have most flexibility 
here. SDL, OpenGL, XRender and DirectFB provide you the required API to 
access this functionality.

The you can use the scaler unit and render the video on the overlay. The 
OSD can get drawn on the second screen/layer. In order to make it 
visible you have to configure the layer transparency and colorkey
appropriatly. This functionality can get accessed through SDL, DirectFB 
and XVideo. Even when these libraries provide a common API to access the 
scaler and layer functionality of the graphics cards the actual hardware 
still significantly differs from vendor to vendor, so you need to 
implement multiple code paths for different graphics cards.

And then you can take the pure software approach, this is the most 
portable but also the most inefficient way and will always require the 
latest'n'greatest processor.

Approach #1 will be the most elegant way and be portable on all modern 
cards, approach #2 will probably perform best on older graphics cards 
but takes much more work. Approach #3 is only suited for people that 
like the java-way of living and have plenty of money to burn.


> > SDL is probably the most portable approach right now, DirectFB provides
> > you the fanciest API designed for STB OSD displays but is native only on
> > the Linux Framebuffer, for all other OSs and Windowing systems you need
> > to install the SDL-DirectFB driver. Not too hard.
>
> Should I go away from the Vidix-lirary and should use another library in the
> first place? What do you suggest?
I must admit that I'm not familiar with Vidix, so I can't say much how 
the other libraries relate to Vidix, but in general it depends on what 
you want to do and how portable you want to be.

The most portable way in the PC/Mac world would be based on SDL or 
OpenGL - if you design your code properly then your code will run on all 
cards that are supported by these libraries: this is virtually all 
available hardware in conjuction with all commonly used operating systems.

When you want to let your code run once on 'real SetTopBoxes' then 
DirectFB is probably your first choice.

I personally would choose OpenGL for a bigger project - SDL and DirectFB 
for smaller ones. If you are interested I can send you off-list some 
codelets for DirectFB and SDL showing how you can implement this.

Holger



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