[Qt-embedded-interest] Double Buffer Graphics Driver

[Tom Cooksey]

> Qt List,
>      I am at a point where I am trying to get the Double Buffer
> Graphics Driver working.  I have been able to implement the driver
> and get it to at least be recognized by the program trying to be
> run.  However there is no display on the LCD from the program.  I
> know the programs run when I use the VNC display.  Here is what I
> did: Built the plug-in (all four files located either at
> QTDIR/examples/qws/dbscreen or on the link above) by invoking qmake
> without the –project option since there is already a .pro file, I
> then simply ran make resulting in the output file which was named
> “libdbscreen.so”.  One way to use the plug-in was to create a
> directory in the application directory, so in my case I created
> analogclock/gfxdrivers and placed libdbscreen.so into it (make sure
> permissions are set).  At this point I could simply run the command
> in the application root directory:
>
> ./analogclock –qws –display dbscreen
>
> The resulting output was ”blit_16(): Image format 0 not supported!”
> continuously being printed on the command line (once per second…
> maybe from the clock actually trying to update the area that
> changed?).  There were no LCD changes but at least the driver was
> recognized and could be run.
>
> I would like to figure this out and think that the blit could be
> manually set?  I simply need to copy over the buffer in memory to
> the /dev/fbo which I have accessed before in C.  There is no mmap
> support on my board (ARM) so the frame buffer test doesn’t work… I
> was hoping that this would be a way to work around mmap problem.

The dbscreen driver still uses the regular LinuxFBScreen, which itself 
uses mmap. I think you need to take a look at the LinuxFBScreen class, 
in particular initDevice & connect and write your own screen driver 
which inherits QLinuxFBScreen and which re-implements initDevice, 
connect & blit.


Cheers,

Tom