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1. Re: "UNDO" & "BACKWARD" not working for brush strokes?
Noel Carboni Nov 4, 2012 1:05 PM (in response to *Rich*)Sounds like a display driver issue, to be honest. If you save the file immedately after the undo that should have removed the brush stroke, then re-open it, is it still there?
If not, and it's just the display not updating, try this:
Go into the Photoshop - Preferences - Performance dialog and try changing to one of the lower Advanced GPU Modes. Failing that, try unchecking the Enable OpenGL Drawing option entirely. Make sure you fully Quit and restart Photoshop after any of these changes before testing.
-Noel
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2. Re: "UNDO" & "BACKWARD" not working for brush strokes?
*Rich* Nov 4, 2012 1:44 PM (in response to Noel Carboni)Thanks Noel. Yes, the problem tested out to be a display-update problem. Once saved and closed, the Undo brush stroke was gone when the file was reopened.
I went to the Advanced Settings under GPU Prefs and discovered the Mode drop-down list was grayed-out with "Basic" listed.
However, I did notice two items shown below that were checked. When I unchecked "Vertical Sync" it cured my problem. Anyone have an idea what Vertical Sync does in PS? Thanks.
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3. Re: "UNDO" & "BACKWARD" not working for brush strokes?
*Rich* Nov 6, 2012 2:25 PM (in response to *Rich*) -
4. Re: "UNDO" & "BACKWARD" not working for brush strokes?
R_Kelly Nov 6, 2012 2:39 PM (in response to *Rich*)Here's some pages explaining some about the different open gl features in cs5:
http://helpx.adobe.com/photoshop/kb/gpu-opengl-support-photoshop-cs4.html
http://helpx.adobe.com/photoshop/kb/gpu-opengl-features-preferences-photoshop.html
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5. Re: "UNDO" & "BACKWARD" not working for brush strokes?
Noel Carboni Nov 6, 2012 3:02 PM (in response to *Rich*)*Rich* wrote:
I still don't know what Vertical Sync pertains to relative to OpenGL Settings. Anyone know? Thanks.
Only Adobe knows the exact implementation under the covers, but what it conceptually does is prevent display updates in the middle of a scan.
Keep in mind that what you see on the screen is sent pixel by pixel, row by row, to the monitor - much as it was done in the time of CRT displays and scanning electron beams, even though today most have LCDs.
Once the last pixel at the bottom has been sent, there is a time called the "vertical sync" time where nothing is sent, before the "scan" starts again from the top.
Setting the "Vertical Sync" option is supposed to limit display updates to only occur only during the vertical sync time.
As Conroy has said, this generally can make a display seem cleaner, as when moving something around you might see part of it moved more than another part without Vertical Sync. This is called "tearing" (as in "tearing a piece of paper in two and having the two parts not line up").
By definition the Vertical Sync option setting causes a difference in the timing and the sequence of display operations, and that may be working around a bug in the display driver on your system. It sounds kind of far-fetched, but it happens more than you might think. Adobe provides all these options to help work around problems.
-Noel
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6. Re: "UNDO" & "BACKWARD" not working for brush strokes?
*Rich* Nov 6, 2012 3:18 PM (in response to Noel Carboni)Thanks much, R_Kelly and Noel.
I cured the "Step Backwards" problem in General Prefs (Enable Flick Panning), but now must decide whether to accept hitting "UNDO" three times to cycle through to where it works on-screen, or disable "Vertical Sync." So far, I have seen no adverse effects of having it disabled, but it's probably just a matter of time.
I could also leave it on and set up two keys on my Wacom Intuos to Step Backward / Step Forward. Maybe the tablet's Touch Ring can be set up for this function.
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7. Re: "UNDO" & "BACKWARD" not working for brush strokes?
Noel Carboni Nov 6, 2012 3:26 PM (in response to *Rich*)I have turned off Vertical Sync myself. There's no real downside.
-Noel
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8. Re: "UNDO" & "BACKWARD" not working for brush strokes?
*Rich* Nov 7, 2012 8:17 AM (in response to Noel Carboni)UPDATE:
I installed the Lion OS 10.7.5 update (from 10.7.4) and now both UNDO and STEP BACKWARDS commands work with Vertical Sync checked in the OpenGL Advance pref settings.
I always wait a bit after an OS update is available before installing so as not to be on the bleeding edge of technology. In this case, I waited too long. Thanks everyone.




