When create a piccture, we need to attach a pixmap to it.
A pixmap only has a depth, which is not sufficant for glamor.
As in openGL texture only has a few internal formats which
is not sufficant to represent all the possible picture
format. So we always transform the picture format to GL_RGBA.
And when we need to read back the picture, we must know the
original picture format. So we have to override create
and destroy picture to track a pixmap's real picture format
if it is attached to a picture.
Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
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