X[Shm]GetImage is slow; what can I do about this?

Joel Dice dicej at mailsnare.net
Wed Apr 6 08:25:46 PDT 2005

On Tue, 5 Apr 2005, Jonathan Lennox wrote:

> On Monday, April 4 2005, "Joel Dice" wrote to "Jonathan Lennox, xorg at lists.freedesktop.org" saying:
>> Also, I noticed a
>> dramatic improvement in XGetImage speed when switching from the free nv
>> driver to the proprietary nvidia driver.  On my nVidia 6600GT under Linux,
>> the performance is excellent.
> Indeed, this has made all the difference!  Getting the entire 1280x1024
> desktop takes approximately 50 ms with the proprietary nvidia driver, and
> smaller damage areas are of course faster.  Thank you!
> What kind of performace could be expected with other graphics cards?

On my nVidia 6600GT (proprietary driver, 1.6GHZ Opteron, 64-bit Linux 
2.6), I can get 1280x1024 in 8ms.  On my ATI Rage Mobility laptop (free 
ati driver, 550MHZ P3, Linux 2.6), 1024x768 (the native res.) takes 216ms. 
When I get home tonight, I'll try it on my nVidia TNT.

As I look over my screen capture code, I find that I am using XCopyArea 
(on a Pixmap obtained from XShmCreatePixmap) instead of XShmGetImage.  I 
honestly can't remember the reason for this, but I'm sure somewhere along 
the line this seemed to make more sense and/or performed better than 
XShmGetImage.  If I have the chance, I'll revisit this.

> -- 
> Jonathan Lennox
> lennox at cs dot columbia dot edu

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