8 Replies Latest reply on Nov 7, 2012 8:17 AM by *Rich*

    "UNDO" & "BACKWARD" not working for brush strokes?

    *Rich*

      After making three consecutive brush strokes in my image:

      Click on Undo once, History list backs up one step, but last stroke remains on screen. Press Undo again (Redo) and History list returns to last position, last stroke is still on screen. Click Undo again, History list backs up one step, but now brush stroke disappears as it should.

       

      Or, after clicking Undo the first time, the brush stroke will disappear if I apply another stroke or enter a command, e.g. add new layer.

       

      After making three consecutive brush strokes:

      Use Backwards command, the History list backs up one step, but brush stroke remains on screen. Use Backwards command a second time, History list backs up another step, the last two brush strokes disappear from screen. Use Backwards a third time, History list backs up another step (now 3 steps total), and the first brush stroke disappears as it should.

       

      These commands work fine when creating three consecutive layers, then undoing or moving backwards.

       

      I am using CS 5.1 for Mac running OS Lion 10.7.4. This problem occurs using either a trackball, Wacom Intuos4 tablet or keyboard shortcuts. Can this be a screen-draw bug in the brush tool? Thanks.

        • 1. Re: "UNDO" & "BACKWARD" not working for brush strokes?
          Noel Carboni Level 8

          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

          1 person found this helpful
          • 2. Re: "UNDO" & "BACKWARD" not working for brush strokes?
            *Rich* Level 1

            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.

             

            GPU-Prefs.jpg

            • 3. Re: "UNDO" & "BACKWARD" not working for brush strokes?
              *Rich* Level 1

              Another discovery:

               

              If "Enable Flick Panning" is not checked in PS General Prefs, the "Step Backwards" problem results if "Vertical Sync" is checked (default) in Open GL Advanced Settings.

               

              I still don't know what Vertical Sync pertains to relative to OpenGL Settings. Anyone know? Thanks.

               

              PrefSetting.jpg

              • 5. Re: "UNDO" & "BACKWARD" not working for brush strokes?
                Noel Carboni Level 8

                *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

                1 person found this helpful
                • 6. Re: "UNDO" & "BACKWARD" not working for brush strokes?
                  *Rich* Level 1

                  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.

                  • 7. Re: "UNDO" & "BACKWARD" not working for brush strokes?
                    Noel Carboni Level 8

                    I have turned off Vertical Sync myself.  There's no real downside.

                     

                    -Noel

                    • 8. Re: "UNDO" & "BACKWARD" not working for brush strokes?
                      *Rich* Level 1

                      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.