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Strangest OS X screenshot …. ever?

Last weekend, I was working on a relatively large--OK, a huge--17.8GB QuickTime movie. This was the raw capture of 35 or so minutes of flying time in X-Plane.

strange screenshotI had the original movie open in QuickTime Player, and I had also exported a notably smaller (200MB) H.264 version, which I was playing with in Motion. Then, for no apparent reason, all heck broke lose--both screens on my system suddenly went 70s psychedelic on me, as seen in the grab at right of a portion of the screen (click for full-size).

In addition to the messed-up colors, things were also not in the right spot on the screen--you can see this with the location of the Smart Folders object in the large screenshot. The system seemed to be working fine; I just couldn't make anything out on either screen--except the menubar (but not the menus themselves). So I used Command-Tab and the 'Q' key to quit various running apps, including QuickTime and Motion.

After quitting nearly everything I had running, the screen returned to nearly normal--the only remaining issue was that objects' shadows were really messed up, showing pieces of other windows instead of a fuzzy gray/black shadow. I logged out and back in, and that fixed that issue.

What this reminded me of, more than anything, was mucking about with my Apple ][ back in the day--if you "poked" some data into the wrong memory locations, you could mess up your display in quite a creative manner! It almost seemed like that's what OS X was doing--I had used all the available RAM, so it started using the video card's RAM for storage instead. Yes, I know this isn't possible, and it's in no way what happened.

Anyway, in five years of OS X usage, this is by far the oddest visual distortion I've ever seen, so I thought I'd share. I was quite impressed that the system itself was still usable--I have yet to restart since that incident, in fact, and all has been fine after the re-login.

12 Comments

  1. Depending on what Mac you are using and video card, Motion will use the Video card's GPU. Somehing could have gotten hosed there. Withe the combination oa a large QT file and Motion viola.

  2. As you say, this is video RAM getting messed up (the same type of thing you did with the Apple ][.) These days VRAM is on the video card, and can get munged if someone does something Bad with a Core Image filter or OpenGL, some VRAM swapping stuff goes wrong in the OS, or generally if there's bugs in GPU code or video driver. If you performed the "hack" to enable Quartz 2D Extreme it could also easily cause this sort of thing.

  3. I saw something very much like this on a friend's iBook right before it had no picture at all, just a black screen. I assume it was a video board failure because the start up sounds were proper.

  4. I get this from time to time with Dashboard if I click while things are zooming. If I just re-activate Dashboard it generally fixes things.

  5. It's probably a bug in the OpenGL driver. QuickTime 7 uses OpenGL to draw onto the screen (in new and updated applications), Motion uses OpenGL for everything, and the Quartz Compositor has used OpenGL for layering windows since 10.2 ("Quartz Extreme").

    As Sam pointed out, the Quartz 2D Extreme component in Tiger has many known bugs (which is why Apple has left it disabled). I've got an open bug report with Apple regarding this sort of corruption involving Q2DX. (although the bug I found was much more minor .. only affecting one portion of a single window, it was 100% repeatable.)

    Applications which use Core Image are also likely to expose bugs in video drivers. In another bug report which I filed with Apple, I demonstrated that a certain combination of effects in Core Image Funhouse will reliably crash on a Radeon X850.

  6. Thanks for the information -- very interesting!

    And no, I haven't applied the 2D Extreme hack. I did at one point (to test the hint about it), but I then disabled it again right away.

    -rob.

  7. I have often had a very similar problem with my 15" 700MHz iMac. Usually corresponding with a video driver related kernel-panic, I have to re-boot. The G4 iMac video GPU is on-board and the heat sink is (in my humble opinion) quite dainty. If my house gets too warm in the summer the problem is aggravated. I have just resigned myself to the reality that the case needs to be cracked open annually. Those dust-bunnies must be blasted to oblivion, and a smidge of thermal paste to re-assemble the CPU heat "path."

    I have had 12 to 15 such kernel panics since 2002. Of course the problem first started well after the warrenty expired when the dust was quite established inside the housing.

  8. Ever since I upgraded to Tiger, this has happened occasionally whenever I switch users. The right side of the cube looks fine, but the left side looks like the screen shot. Pressing command-R on a Dashboard widget will do it too, but only where the widget was. The 10.4.3 update seems to have reduced the occurrences of these, however.

  9. I had a similar-looking problem not too long ago that ended up being persistent.

    It started out as a few misplaced pixels, gradually taking the shape of vertical lines down the screen. Eventually it became distorted much like your screen above.

    I was just about to send it back to Apple, but they had me reset the power manager on my ti-book to (mostly) fix it.

  10. Being able to boot XP on a mac was no longer Apple's decision, rendering much of this discussion moot. See http://www.onmac.net and do a little googling for "narf and blanka".

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