nanogui: Microwindows and non zero screenbase
Subject:
RE: [nanogui] Microwindows and non zero screenbase
From:
Fabrice Gautier ####@####.####
Date:
27 Mar 2002 03:03:54 -0000
Message-Id: <B1F6452C89AFD411AE0800A0CC734C239DBB9F@EMAIL1>
> -----Original Message-----
> From: Greg Haerr ####@####.####
> Sent: Tuesday, March 26, 2002 6:33 PM
> To: Fabrice Gautier; Nanogui (E-mail)
> Subject: Re: [nanogui] Microwindows and non zero screenbase
>
>
> > psd->addr = mmap(NULL, psd->size,
> > PROT_READ|PROT_WRITE,MAP_SHARED,fb,0);
> >
> > In my case the video buffer doesnt start on a page boundary
> > so the mmaped memory start a few bytes earlier. In the linux
> > framebuffer driver this information is stored in screen_base
> > in an fb_info struct,
>
> You should be able to just add in your offset to psd->addr:
> psd->addr += fb_info.screen_base;
> Microwindows doesn't assume anything about psd->addr
> except that it's the start of the drawable hw framebuffer.
Actually this is a bot more complicated, because:
1/ There's no way to get an fb_info struct from the driver.
2/ The only thing you can get is the _physical_ address of the drawable
buffer, so that in order to get the offset you have to play with PAGE_MASK.
3/ When you munmap, you also have to find a way to give the same address
that you get from mmap (and not the drawable buffer)
I tried to do that but it didnt work at the first try, so instead i fixed
the kernel framebuffer driver so that only the drawable buffer is mmap (this
is much better anyway)
The thing is that X handled this case pretty well so the problem was not
aparent at first.
Thanks
