how glx extension uses the software render

[Wang Baisheng]

Dear Rahaman,

Thanks again!

You mean that if I build X with DRI support, all redering request are all 
dispatched to the X Server regardless of loading the DRI driver success of 
failure ?

And another question, which is I asked before, if the DRI setup failed, how 
the xserver bypassed the rendering request to Mesa to render?  Would you 
please give me some glue at code level ?

Thanks,
Regards,
Baisheng

On Friday 06 March 2009 02:05:56 am Mustafizur Rahaman wrote:
>  Hi,
>
>  While replying your previous email, i had the doubt whether you are
> talking about dispatching the gl APIs or dispatching the glX APIs because
> you mentioned "How glx extension requests are dispatched"...so i thought
> you are mainly asking about dispatching of glX APIs :-)..So, anyway below
> are my responses...
>
>  Wang Baisheng wrote:
> Dear Rahaman,
>
> Thank you for answering my questions! Great!
>
> And I have read some docs about dri and aiglx. But Maybe I misunderstand
> them. They all say that when using indirect render, it's the glx module
> with X server will dispatch the request to Mesa. Pls refer :
> http://dri.sourceforge.net/doc/dri_data_flow.html
> http://dri.sourceforge.net/doc/dri_control_flow.html
>
>
> And another slide in a ppt named 'Accelerated Indirect GLX' written by
> Kristian Høgsberg on XDevConf , 9 Feb 2006 :
> ======================
> Indirect rendering
>
> If the server doesn't support DRI, if part of the DRI setup fails or if the
> users 
> specifically asks for it, libGL will fall back to indirect rendering.
>
>  <Rahaman>: I don't think it depends on whether the server supports DRI.
> Because DRI means direct rendering from client side, thus bypassing the
> server altogether.So, as far as i know & i have seen from the mesa code
> also, that the DRI setup is being done from the client side using the XF86
> DRI API and if the setup fails, it automatically goes for indirect
> rendering.
>
>
> In indirect mode, all OpenGL requests are marshalled to the server and libG
>L is  reduced to just a protocol layer.
>
>  <Rahaman>: If it is only indirect mode, then you are right. But there is
> something called AIGLX(accelerated indirect), where the requests are first
> passed to the server & then the xserver dispatch those GL request to the
> libGL and DRI driver to render on the framebuffer(Here the same libGL is
> linked to both the client program and thr xserver).
>
> In the server, the GLX module maintains an OpenGL context on behalf of the 
>   client and forwards the demarshalled requests to the context.
>
>  <Rahaman>: For indirect/AIGLX mode, it is correct assumption.
>
>
> The current implementation pulls parts of Mesa into the Glcore module to pr
>ovide  a software backed GL context.
>
>  <Rahaman>: This is something which i had asked before and got answered,
> but don't remember them exactly right now:-(
>
> Synonymous with software/slow rendering
> =====================
>
> It also said that "The current implementation pulls parts of Mesa into the
> Glcore module to provide a software backed GL context."
>
>
> But when I look the code of xm_api.c, I found it seems that in indirect
> mode, libGL is not just a protocol layer, and the client use its software
> render functions directly and those software render functions just like a
> normal  X client using xlib api.
>
> So can I say so that when in software render mode, it's not X server glx
> module dispatch the requests to Mesa, while it's the client using the libGL
> software render functions directly ?
>
>  <Rahaman>: You are correct. xm_api.c will be only be built if you are
> building mesa ONLY for indirect mode, i.e. you are not using any h/w
> accelerated GL library/DRI driver. In that case, complete rendering is
> being taken care in s/w by mesa & the final o/p is being sent to xserver to
> render onto the frame buffer.
>
>  You should remember that you can compile mesa for dri & indirect mode.If
> you built it for indirect mode, everything taken care in s/w & the final
> o/p is being sent to xserver.
>
>  If you built it for DRI mode & in run time, DRI setup successds, then it
> will run in DRI mode.But, in run time, the DRI setup can fail and in that
> case, request will still be sent to xserver but then xserver will by pass
> them to mesa to render.
>
> Thanks!
> Regards,
> Baisheng
>
>
>
>
> On Thursday 05 March 2009 04:56:57 am Mustafizur Rahaman wrote:
>
> Hi,
>
> I also faced the same problem sometime back , but any how after lot of
> debugging and analyzing the code, i have got some sort of understanding,
> which i am sharing.If anywhere, my understanding is not correct, i
> apologize for that.
>
> Check for these three files  1>glxcmds.c & glxext.c & 2> glxapi.c in
> mesa code. If you see the Makefiles, glxcmds.c & glxext.c is built for
> direct rendering & glxapi.c is built for indirect rendering, not both of
> them are built at the same time with the client program.
>
> So, let's take glxgear.c code for example and track the code flow, e.g.
> following would be the code flow for glXCreateContext for indirect
> rendering case..
>
> glXCreateContext==>Fake_glXCreateContext==>XMesaCreateContext==>_mesa_initi
> alize_context==>_mesa_init_exec_table==>Inside here, you can see all the
> mesa s/w functions are initialized.
>
> For direct rendering case, the following would be the flow...
>
> glXCreateContext==>XF86DRICreateContextWithConfig==> Then it goes to dri
> driver's create context and like this...
>
> I would request you to debug the code for indirect rendering for glxgear
> and see the code flow.And paralelly, try to follow the code flow for
> direct rendering(by code reading if you can't debug)..that's the way i
> followed...
>
> Have patient..because believe me, you will need that.. :-)
>
> Regs,
> Rahaman.
>
> Wang Baisheng wrote:
>
> Dear all,
>
> Now I am studying the DRI. But I have some questions and I can not get
> more information from internet. So would you please give me some
> information for my following questions:
>
> How glx extension requests are dispatched to mesa for software render?
> And how glx extension requests are dispatched to DRI driver ? And I also
> find in x server 1.3, there is a glcore, but in x server 1.5, the glcore
> is disappear.
>
> Thanks!
> Regards,
> Baisheng
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