[Gambas-user] RE Jpeg Perfomance

[James Wilson]

 On Tuesday 03 January 2006 20:55, Rob Kudla wrote:
> On Tue January 3 2006 14:02, nando wrote:
> > Shelling to a 3-line Shell script (a different one for each
> > camera):
>
> You might also consider using "convert" or some other ImageMagick tool

> run from a shell without a WAIT to do the stretching, so that 4 of 
> those can be done at the same time too.  It won't be any faster than 
> Qt's stretching, but at least your program isn't frozen while it's 
> happening.
>
> Also, using a drawing area is slower than using two picture boxes for 
> each image and showing/hiding them (basically page flipping) in my 
> experience.

Cached drawing area or not?

> I wrote an app to capture and display frames from a security camera 
> (by shelling out to some v4l capture utility), and I used that 
> approach.  Qt is still slow enough that when you make the picture 
> full-screen you can see the redraw, but short of redoing it as an SDL 
> app I don't see any other option.

Maybe you could use the gb.v4l component of Daniel?

First, by default, stretching is antialiazed. By passing FALSE as third
argument of Stretch, things will be quicker.

Anyway, stretching is slow, especially to half the size of the desktop.
It is written in pure C, and does not use any MMX/SSE x86 instruction.

A good idea would be integrating the stretch feature inside the X
server. It would be faster: you will send only the initial image to the
X server, not the result of the stretching, that may be very big.

>
> When gb.qt.opengl is mature, you might look into that for faster
> scaling as well.

Maybe you can already use it for that - I don't know, Laurent Carlier
will 
tell about that.

Regards,

-- 
Benoit Minisini


I have tried it without the scale/stretch and things improve a bit but
not by a huge amount. If there is only 1 image being shown it has
acceptable performace, but ultimatly I want to have 16 images displayed
this way. I think I need to find another way lol. I tried the show hide
thing suggested but must have got the sequence wrong as it still
flickered. 
As it currently stands you can see the image being refreshed vertically.
Im assuming the stretch has already been performed before it gets to
displaying it. IT seems to be a speed issue in actually drawing the
images. Thanks for your answers though.

BTW when running this app it gbx takes all available resources ie all
available processor a 2200 XP (91%) and 50% of the 512Meg installed in
my test machine