Re: MIT-SHM example

["Rose Cumming" <rose_alice_cumming hotmail com>]

thanks for your replies anyways. I'm studying some rationales related to 
what you said.

I have some working code that has a refresh rate of over 24fps on a 
relatively small window (using gdk drawing primitives). I also played with 
gtkglextmm

since you suggested,
"using XImage has a number of costs *regardless* of whether MIT-SHM is
present or not. it is *not* the fastest way to draw an image all the
time",

say for example, to render on a nearly full-screen window (say the screen 
has a resolution of 1280x1024pixels) in a timely fashion, like a video 
player. with raw RGB input data.

What will be your suggestion for a fast way? say targeting at a 20-24fps?
you know how MPlayer or Xine does graphics rendering?


> From: Paul Davis <paul linuxaudiosystems com>
> Reply-To: paul linuxaudiosystems com
> To: Rose Cumming <rose_alice_cumming hotmail com>
> CC: gtkmm-list gnome org
> Subject: Re: MIT-SHM example
> Date: Mon, 19 Sep 2005 23:07:16 -0400
>
> On Mon, 2005-09-19 at 16:44 +0000, Rose Cumming wrote:
> > I'm not confused.
> > My application (client) and the X server are running on the same 
> machine.
> >
> > I want to have very high frame rates to playback my raw data images.
> > I have tried drawing primitives like draw_rgb_image and draw_gray_image.
> >
> > What you said was consistent with previous email archieves I read. Using
> > MIT-SHM will avoid network flow because the image (Xmage) use shared 
> memory
> > when the client and server are on the same machine.
> > I have this link
> > http://ftp.xfree86.org/pub/XFree86/4.5.0/doc/mit-shm.txt
> > that talks about shared memory XImage.
> >
> > but if anyone has working example of how to set up a simple application, 
> it
> > would be greatly appreciated.
>
> i am afraid that you *are* confused. controlling the use of MIT-SHM is
> not intended to be an option for an application. the version of Xlib
> that you are linked against will check whether the server supports it.
> if the server does support it, then any realworld Xlib implementation
> will use it.
>
> using XImage has a number of costs *regardless* of whether MIT-SHM is
> present or not. it is *not* the fastest way to draw an image all the
> time - that depends a great deal on what the image is, on the type of
> the server, the host system you are running on, and more.
>
> if you want to draw images quickly, please forget about MIT-SHM. it is
> not an important part of the code you will write. there are reasons to
> prefer using a client side image on occasion; there are reasons to
> prefer a server side image on other occasions. these reasons exist and
> are true with *and* without MIT-SHM.
>
> >I want to use low level Xlib drawing API with a Gtk::DrawingArea.
> >My application is targeted on a single host machine. So I want to use
> >the fastest way to draw images possible.
>
> Why on earth do you imagine that using gdk routines, which normally map
> 1:1 onto Xlib routines, will be measurably slower than Xlib routines? if
> your frame rate is slow, you should look to your algorithms for drawing
> and for the overall structure of your code.
>
> People use GDK/GTK to get frame rates that are essentially identical to
> what they would get if they had raw access to the h/w. *Without* using
> Xlib, and without even stopping to think about whether or not MIT-SHM is
> present or not.
>
> --p

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