[maemo-developers] Can GTK+ make use of XSHM extension from MIT

[From: Eero Tamminen]

Hi,

ext Bin Chen wrote:
>> ext Bin Chen wrote:
>>> I am not doing very detailed profiling against this, but by comparing
>>> the frame rate in my player against using pure framebuffer
>>> implementation. The performance difference is large. If not using
>>> shared memory to transfer the decoded image data, obviously the
>>> performance can't be good in slow machine.
>>>
>>> The GTK+ can draw pixbuf and image to the drawable, is there any
>>> existing method for me to choose to force the low level gdk to use SHM
>>> extension?
>> If you have a local connection to X server it uses that
>> (where it helps, setting up XSHM has its own overhead).
>>
>> Gdk handles images internally as 32-bits, the display is 16-bits.
>> Conversion is done automatically when needed by Gdk.  Need I say
>> more?
>>
>> It sounds like your use-case would be more appropriate to be done
>> with libSDL (which also does automatic conversions, but can handle
>> surfaces in display bit-depth if you've just asked it to do that).
> 
> Ok, let me make the things clear, the content in a gdk window includes
> many widgets, such as label, entry, button. But from the perspective of
> X server, this widgets are just bitmaps with the states updated by GTK+,
> right?

That detail depends on which theme engine you use.

With maemo Sapwood engine all the currently required client widget
bitmaps are at the X server side (at display bitdepth i.e. as 16-bit)
and shared between all the applications.

With pixbuf engine all widget images are in the application process
as normal gdk_pixbufs (i.e. 32-bit) and converted to display format
on each blit.

Most other older theme engines draw things instead using bitmaps.
Newer themes use SVG sources, but could cache them as bitmaps.


> Xshm will accelerate the client to server transfer for type of Image and
> Pixmap, but the GTK+ use XCopyArea to update the bitmap, can XCopyArea
> can benefit from the Xshm?
> 
> In more detail, I am using gdk_draw_image to draw an image to a gdk
> drawable, will this benefit the Xshm?

Gdk does all image operations in 32-bits, N800/N810 display is 16-bit.
Whether you use SHM or not can be of less concern than this from the
performance point of view.


> Of course, my GTK+ built with Xshm enabled and from Xdpyinfo the Xshm is
> enabled in X side.


	- Eero