Created attachment 48502 [details]
demo video of distorted icon while doing drag & drop

Created attachment 48503 [details]
systeminformation

First mentioned in bug 38021. I've not been able to reproduce this using Onieric.

I suspect the answer lies in mesa, and that

diff --git a/src/sna/sna_dri.c b/src/sna/sna_dri.c
index b75c46e..33247de 100644
--- a/src/sna/sna_dri.c
+++ b/src/sna/sna_dri.c
@@ -187,7 +187,7 @@ sna_dri_create_buffer(DrawablePtr drawable,
 
        pixmap = NULL;
        bo = NULL;
-       usage = CREATE_PIXMAP_USAGE_SCRATCH;
+       usage = 0;
        switch (attachment) {
        case DRI2BufferFrontLeft:
                pixmap = get_drawable_pixmap(drawable);

will paper over the bug.

*** Bug 38021 has been marked as a duplicate of this bug. ***

There is very little point debugging these whilst unity is in such a state of disrepair. valgrind has a lot to say about their rendering code, and everything else.

I am experiencing the same bug when I drag some selected text in chromium. The window manager is xfwm4 with compositing enabled. However there are some conditions to trigger this behaviour.

If I open a new chromium instance, select a relatively small piece of text (1 or 2 lines) and drag that around, the box contains random stuff. This goes on as long as I subsequently select a larger piece than the previous one. However, when I select a piece of text that is smaller than the previous one, everything is ok (mostly). If I just select a lot of text (more than 20 lines), the dragged text appears fine either and any following drags are fine, too.

I can reproduce this with SNA enabled with and without the patch posted by Chris in this bug on my 945GM.

Thanks, I can reproduce the xfce4+chromium issue easily. My first thought was that it was a Y-tiling issue, but I suspect not now having disabled all Y-tiling. :(

commit a5b5b4ebb14cab19258dd1cbc12721aaa9df226d
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sat Sep 17 00:28:30 2011 +0100

    sna: Apply the screen offset for direct upload of a composited pixmap
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38733
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>