How to edit Drawable/XdbeBackBuffer data?...

Adam Jackson ajax at
Mon Aug 20 12:17:49 PDT 2012

On 8/20/12 2:08 PM, Lee Fallat wrote:
> Hey,
> I'm trying to darken/lighten the image data in a Drawable/XdbeBackBuffer.
> Any ideas on how to get access to the data?...I've done an XGetImage() on
> Drawable but that really slows down the application I'm editing...

That is, in fact, how you do it.  GetImage is not fast.  ShmGetImage is 
faster, and as fast as you're going to get, if you insist on doing this 
by pulling all the pixels down to the client and then pushing them back up.

You may instead wish to use the Render extension, which gives you the 
usual set of Porter-Duff blend operations, and which runs in the server 
so you're not copying all that data around.

- ajax

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