Impact of changing default Screen depth on other XO Apps

shivaprasad javali jbsp72 at
Wed Jan 27 08:11:22 EST 2010

We are allocating a 32 bit buffer and then using the X server calls to blit
it to the 16 bit screen. Even this is slowing down the application as the
draw in the application is very intensive. We commented out parts of our
draw code to find out the part which was slowing it down and found that the
blit to the 16 bit screen ( using X server calls) was responsible for a
large chunk of the slowdown. When we changed the screen depth the
performance of the activity increased dramatically.

I was worried if some other activity on the XO making the opposite
assumption and optimizing their draw code for a 16 bit screen and then
suffering because we changed the default depth.


2010/1/27 NoiseEHC <NoiseEHC at>

>  Since you can only blit pictures on an X server and cannot get a direct
> pointer to the video memory, I do not know what your problem is. You can
> just allocate a 32 bit offscreen buffer in the address space of your
> application and blit it via the X server to the 16 bit video memory (draw).
> The XO-1 has bit depth converter hardware so it will not be slower in
> theory.
> Note that you cannot use the video overlay for this because it has only YUV
> and RGB-565 modes on the XO-1 and there is a bug in X that the overlay will
> be garbage after a suspend and it was not fixed last time I checked. (I have
> told that I would fix it but because I could not figure out how to compile
> stuff for the XO-1 - like recompiling the kernel and the X server - I did
> not fix that.)
> If you need it then I could search for the code I have used but it would
> take some time...
> shivaprasad javali wrote:
> Hi All,
>         We are developing an Activity for the XO. During development we ran
> into an issue with the default screen depth on the XO. Our application
> assumes that the screen depth is 32 and does all the draw math. But as the
> screen depth on the XO is 16 we had to do constant 32 bit- 16 bit
> conversions which really hit performance. So we put in script to run after
> installing our activity which changes the default screen depth on the XO
> from 16 to 32 bit.
>         I wanted to know how much of an issue this would be for other
> activities running on the XO. Would they be adversely affected by this
> change?
> Thanks
> Shivaprasad
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