Re: Desktop Capture (Vista)
- From: SachinS <SachinS@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 1 Jul 2007 22:00:04 -0700
Hi Ivan,
Thanks for your explanation.
Now I have one more thing to ask, I have created a application which
captures the screen (yes DWM composed screen). My screen area is 1280x1024
(32bit depth). I read the screen 10 times and each time I stored the
difference, with previously captured screen. Till here this process takes
600-700 milliseconds. My machine configuration is 2.8 GHz HT Pentium 4
processor, 512 MB RAM, Windows Vista Business with AERO theme. And when I
save the last image on disk the whole process takes nearly 900 milliseconds.
Will it be feasible enough to read screen in this way? Instead of thinking
about drivers can’t I use this approach, and I don’t think there is need to
read screen for more than 4-5 times per second.
I understood that the composition of whole desktop is dependent on GPU. But
I think Present function is there which says, “now this rendered screen need
to display”. Can’t this used to know when a new desktop screen available?
--
SachinS
"Ivan Brugiolo [MSFT]" wrote:
With Desktop composition active, the final sceen you see on the screen.
is assembled (by MilCore.dll) using the Direc3D 9.l runtime.
It mens that the result of the rasterization process is known only to the
GPU
and the RAMDAC, and, nodody else in the system has physical access to it.
On average implementation of the current generation of hardware, it may
be mapped in aperture memory, and, it might be accessible
(in HIV propetary swizzled format, for example), but, it would be non
decodable.
In order to support the screen capture functionlity, the desktop compositor
runs a render-pass to an off-screen render target, and, copies that content
in a system-memory accessible surface of a known pixel format.
That is what the system does with desktop-composition on when you copy
from a Device Context obtained via GetDC(NULL).
That explained, you should see why a display driver (a mirror driver is
a display driver) is not in use while composing the desktop.
Catching a snapshot of a single window with a mirror driver,
while desktop composition is active, is not supported today.
--
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"SachinS" <SachinS@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:498ACAD0-7550-4493-898F-2FBC19945053@xxxxxxxxxxxxxxxx
Hi Tim,
Thanks for your response , but sorry I could not understand, your comment
is
for what.
And you said, "So, in the end, you might be able to catch a snapshot of a
single window, but it may simply be impossible to capture the whole
screen.". This is for Mirror Driver?
Can you please make it clear... what you want to say...
--
SachinS
"Tim Roberts" wrote:
SachinS <SachinS@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Now one more thing:
I have read somewhere that in future Microsoft may remove support of
Mirror
Drivers because it is based on old Windows 2000 driver technology/model.
And
Microsoft don't want to remove advanced visual effects, which can be
done
with new graphics cards. So how applications, which will capture Desktop
for
remote display, will work. There must be a solution, which can work with
future versions of Windows.
Not necessarily.
There is a reason why the traditional mirror driver won't work with Aero.
In that mode, the desktop that you see does not necessarily exist in
memory
ANYWHERE. The image is composed on the fly during refresh.
So, in the end, you might be able to catch a snapshot of a single window,
but it may simply be impossible to capture the whole screen.
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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