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Re: OPENSTEP 4.2 vmware SVGA

From: Pascal Bourguignon
Subject: Re: OPENSTEP 4.2 vmware SVGA
Date: Wed, 23 Jan 2002 21:58:41 +0100 (CET)

Frederic Stark <address@hidden> wrote:
> Hi,
> Boring weekend. I took my OS42 CDs, vmware, the diff to the vmware 
> module of XFree86, the drivers example from OS42, a dozen of cup of 
> coffee and started to hack an OPENSTEP42 vmware SVGA driver.
> I am to the point where I get it running in 1024x768/24bits (yep, the 
> values are hard-coded for now). Code is _very_ ugly, as this is my first 
> OS42 driver (OS42 have no documentation on the DriverKit, and I can't 
> get my hands back on my 3.3 CDs). I can probably get something more 
> usable next week-end. I can release what I have for the impatient, of 
> course.
> The problem is that the DPS server never tell my driver when screen have 
> been written to, so vmware don't know when to update the real screen 
> (ie: there are 'phantoms' left in a lot of places). I don't think the 
> NeXT window server was ready to work with a 'buffered' device.
> Any idea about how I can solve that ? I can think about several solutions:
> 1/ Don't care (by moving the vmware window, the 'phantoms' disapear 
> because vmware flushes the screen)
> 2/ Implement a /dev device and a user-land utility to tell the driver to 
> flush the screen (every one second, for instance).
> 3/ Get a PostSript master to try to hack WindowPackage.ps to know if the 
> server did something. Alternatively, I could try to patch the 
> WindowServer binary.
> 4/ Play with mach memory to know if window server wrote to the 
> framebuffer. Issue a flush to vmware 1/10th of a second later. It must 
> be possible, but I have the slighest clue about how to do it.
> Any other trick ?

The best  solution would be something like  3/, to have a  hook in the
low-level    DPS     raster    routines.    That     would    be    in
/usr/lib/NextStep/WindowServer, but it's  death-row software, not free

But it would  be enough to have your driver  flush automatically 10 or
20 times  a second. Since flushing  to the screen could  be costly, it
may be interesting to divide the  frame buffer of your driver in tiles
and compute  a md5sum over  each tile, and  flush only the  tiles that
have changed.

Since there are the blinking carets, the clock, the cursor, the screen
will need updating continuously, in small parts of it at least.

The check sum computing frequency could be varied depending on whether
the tile or its neighbor changed recently or not.

__Pascal_Bourguignon__              (o_ Software patents are endangering
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