[Webkit-unassigned] [Bug 21495] DRT tool needs to capture real "on screen" window content

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=21495


pol at apple.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Need "--onscreen" option on |DRT tool needs to capture
                   |DRT tool                    |real "on screen" window
                   |                            |content




------- Comment #9 from pol at apple.com  2008-10-10 16:25 PDT -------
More investigation showed that CGWindowListCreateImage() works correctly even
if the window is not visible (i.e. outside of the screen bounds), as long as
it's ordered in. This includes capturing the surface on top of the window.

One point of interest is that in case of multiple video cards configurations,
windows out of the screens area are assumed to be on the primary video card
(this matters for OpenGL virtual screen).

Note that CGWindowListCreateImage() is only available on Mac OS X 10.5 and
later, and there's no satisfying replacement on earlier OS. You could read from
the framebuffer directly, but this involves OpenGL and require the window to be
both visible and un-occluded on screen.

Finally, the image you get through CGWindowListCreateImage() very slightly
differs from the one you get by reading the window backing buffer as the window
server compositing path gets involved. Practically, this means there are very
small dithering artifacts (at least on my iMac).


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