# Flip, dontclear Flag **URL:** \ **Category:** Uncategorized\ **Created:** [November 8, 2008, 5:22am UTC](https://psychtoolbox.discourse.group/t/flip-dontclear-flag/644 "2008-11-08T05:22:21Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![ah\_javadi](https://avatars.discourse-cdn.com/v4/letter/a/b5ac83/32.png) [@ah\_javadi](https://psychtoolbox.discourse.group/u/ah_javadi)\ **Post date:** [November 8, 2008, 5:22am UTC](https://psychtoolbox.discourse.group/t/flip-dontclear-flag/644/1 "2008-11-08T05:22:21Z")
Hello, I have problem with "dontclear" flag in Screen('Flip') command. Simply when I run the demo file "MouseTraceDemo2.m" it gives me the following error and jumps out of the program. +++++++++++++++++++++++++++ Error in function Flip:     Usage error OpenGL AUX buffers unavailable! dontclear=1 in Screen-Flip doesn't work without them. Either unsupported by your graphics card, or you disabled them via call to Screen('Preference', 'ConserveVRAM')? Usage: % Activate compatibility mode: Try to behave like the old MacOS-9 Psychtoolbox: oldEnableFlag=Screen('Preference', 'EmulateOldPTB', [enableFlag]); > \>\>\> and the "help Screen" comments and then ??? Usage: [VBLTimestamp StimulusOnsetTime FlipTimestamp Missed Beampos] = Screen('Flip', windowPtr [, when] [, dontclear] [, dontsync] [, multiflip]); Error in ==\> MouseTraceDemo2 at 82     psychrethrow(psychlasterror); +++++++++++++++++++++++++++ I also add the command line below prior to the Flip command, but still it is the same. oldEnableFlag=Screen('Preference', 'EmulateOldPTB', 1); I'm using PTB 3 under Windows XP in Bootcamp (Sorry for degrading from MAC. Actually I love my machine's MAC side but I need to write this program in windows OS. It's terrible!). I have a 2 x Quad Xeon Intel MAC computer with video card ATI Radeon HD 2600 XT with driver version 2.1.7273. What should I do? Thanks for your attention. Best Amir ---
**Author:** ![mariokleiner](https://avatars.discourse-cdn.com/v4/letter/m/13edae/32.png) [@mariokleiner](https://psychtoolbox.discourse.group/u/mariokleiner)\ **Post date:** [November 9, 2008, 4:28am UTC](https://psychtoolbox.discourse.group/t/flip-dontclear-flag/644/2 "2008-11-09T04:28:48Z")
Search the forum, this has been answered multiple times. > --- In [psychtoolbox@yahoogroups.com](mailto:psychtoolbox@yahoogroups.com), "Amir Homayoun Javadi" \ wrote: > \> > \> Hello, > \> > \> I have problem with "dontclear" flag in Screen('Flip') command. Simply when > \> I run the demo file "MouseTraceDemo2.m" it gives me the following error and > \> jumps out of the program. > \> > \> +++++++++++++++++++++++++++ > \> > \> Error in function Flip: Usage error > \> OpenGL AUX buffers unavailable! dontclear=1 in Screen-Flip doesn't work > \> without them. > \> Either unsupported by your graphics card, or you disabled them via call to > \> Screen('Preference', 'ConserveVRAM')? > \> Usage: > \> > \> % Activate compatibility mode: Try to behave like the old MacOS-9 > \> Psychtoolbox: > \> oldEnableFlag=Screen('Preference', 'EmulateOldPTB', [enableFlag]); > \> > \> \>\>\> and the "help Screen" comments and then > \> > \> ??? Usage: > \> > \> [VBLTimestamp StimulusOnsetTime FlipTimestamp Missed Beampos] = > \> Screen('Flip', windowPtr [, when] [, dontclear] [, dontsync] [, multiflip]); > \> > \> Error in ==\> MouseTraceDemo2 at 82 > \> psychrethrow(psychlasterror); > \> > \> +++++++++++++++++++++++++++ > \> > \> I also add the command line below prior to the Flip command, but still it is > \> the same. > \> > \> oldEnableFlag=Screen('Preference', 'EmulateOldPTB', 1); > \> > \> I'm using PTB 3 under Windows XP in Bootcamp (Sorry for degrading from MAC. > \> Actually I love my machine's MAC side but I need to write this program in > \> windows OS. It's terrible!). I have a 2 x Quad Xeon Intel MAC computer with > \> video card ATI Radeon HD 2600 XT with driver version 2.1.7273. > \> > \> What should I do? Thanks for your attention. > \> > \> Best > \> Amir > \> ---
**Author:** ![ah\_javadi](https://avatars.discourse-cdn.com/v4/letter/a/b5ac83/32.png) [@ah\_javadi](https://psychtoolbox.discourse.group/u/ah_javadi)\ **Post date:** [November 9, 2008, 5:13am UTC](https://psychtoolbox.discourse.group/t/flip-dontclear-flag/644/3 "2008-11-09T05:13:41Z")
Hello, Dear Mario Sorry for posting the comment before checking the forum. OK. I followed two of the solutions gone below [theWindow,theRect] = Screen('OpenWindow', whichScreen, 0, [], [], [], [], [], kPsychNeedFastBackingStore); and PsychImaging('PrepareConfiguration'); PsychImaging('AddTask', 'General', 'UseVirtualFramebuffer'); [theWindow,theRect] = PsychImaging('OpenWindow', whichScreen, 0); interestingly they can be ran for just one time. For the second run both of the solutions give the following error Error in function OpenWindow:     Usage error Sorry, imaging pipeline functions are not supported in OS-9 PTB emulation mode. To resolve it, I ran the following commands before my second run clear all close all and it is working now. What is the possible cause for that? And after a while even when I commented the above clear and close commands, the program works fine. Have I missed anything? And what is difference between these two approaches? Thanks for your reply. Amir 2008/11/9 Mario Kleiner \<[mario.kleiner@...](mailto:mario.kleiner@...)\> > > Search the forum, this has been answered multiple > > times. > > > > > > > > --- In [psychtoolbox@yahoogroups.com](mailto:psychtoolbox%40yahoogroups.com), "Amir Homayoun Javadi" \ wrote: > > \> > > \> Hello, > > \> > > \> I have problem with "dontclear" flag in Screen('Flip') command. Simply when > > \> I run the demo file "MouseTraceDemo2.m" it gives me the following error and > > \> jumps out of the program. > > \> > > \> +++++++++++++++++++++++++++ > > \> > > \> Error in function Flip: Usage error > > \> OpenGL AUX buffers unavailable! dontclear=1 in Screen-Flip doesn't work > > \> without them. > > \> Either unsupported by your graphics card, or you disabled them via call to > > \> Screen('Preference', 'ConserveVRAM')? > > \> Usage: > > \> > > \> % Activate compatibility mode: Try to behave like the old MacOS-9 > > \> Psychtoolbox: > > \> oldEnableFlag=Screen('Preference', 'EmulateOldPTB', [enableFlag]); > > \> > > \> \>\>\> and the "help Screen" comments and then > > \> > > \> ??? Usage: > > \> > > \> [VBLTimestamp StimulusOnsetTime FlipTimestamp Missed Beampos] = > > \> Screen('Flip', windowPtr [, when] [, dontclear] [, dontsync] [, multiflip]); > > \> > > \> Error in ==\> MouseTraceDemo2 at 82 > > \> psychrethrow(psychlasterror); > > \> > > \> +++++++++++++++++++++++++++ > > \> > > \> I also add the command line below prior to the Flip command, but still it is > > \> the same. > > \> > > \> oldEnableFlag=Screen('Preference', 'EmulateOldPTB', 1); > > \> > > \> I'm using PTB 3 under Windows XP in Bootcamp (Sorry for degrading from MAC. > > \> Actually I love my machine's MAC side but I need to write this program in > > \> windows OS. It's terrible!). I have a 2 x Quad Xeon Intel MAC computer with > > \> video card ATI Radeon HD 2600 XT with driver version 2.1.7273. > > \> > > \> What should I do? Thanks for your attention. > > \> > > \> Best > > \> Amir > > \> ---
**Author:** ![mariokleiner](https://avatars.discourse-cdn.com/v4/letter/m/13edae/32.png) [@mariokleiner](https://psychtoolbox.discourse.group/u/mariokleiner)\ **Post date:** [November 9, 2008, 6:33pm UTC](https://psychtoolbox.discourse.group/t/flip-dontclear-flag/644/4 "2008-11-09T18:33:35Z")
This is a funny one, a nice little "chain reaction". The error in Screen('Flip') triggers the error handling in the catch clause inside Mousetracedemo2, there a function Screen('ShowCursor') gets called, but no such function exists (a call to ShowCursor; would have been correct). In response, the Screen command prints out its overview of all commands - the same you'd get by simply typing Screen + Enter. You followed the "instructions" to enable PTB-2 compatibility mode (which actually weren't instructions but simply the topmost output of the command overview), then at next run of a demo PTB was switched into this compatibility mode, which doesn't support most of the new functions so you got that error message. A "clear all" resets everything -- and is actually highly recommended after a script aborts with some error for that reason. So after "clear all", PTB was again in its normal PTB-3 mode and everything worked. So: 1. We need to fix those demos error handling. 2. If in doubt, after any error, type "clear all". 3. Screen retains its Screen('Preference',...) settings until you change them or do a clear all. 4. Some of our M-Files internally cache some settings across invocations to save computation time, so after an error abort, they may be in an undefined state, unless clear all is called. The compatibility mode is only to help people with ancient PTB-2 code to keep that code working on PTB-3 or at least to simplify porting of that code to PTB-3. It's a band-aid, not recommended for new code, and even for old code one would be better off porting the code properly. Most interesting new features get disabled in compatibility mode. The difference between > \> [theWindow,theRect] = Screen('OpenWindow', whichScreen, 0, [], [], [], [], > \> [], kPsychNeedFastBackingStore); > \> > \> and > \> > \> PsychImaging('PrepareConfiguration'); > \> PsychImaging('AddTask', 'General', 'UseVirtualFramebuffer'); > \> [theWindow,theRect] = PsychImaging('OpenWindow', whichScreen, 0); > \> is exactly zero. The latter internally invokes the former, but only in this simple special case. Use the PsychImaging interface. It provides many useful functions and performs all the complex'n dirty low-level setup work for you, takes care of special cases, workarounds for broken hardware and drivers etc. help PsychImaging for an overview. The latter is easier to use and understand in 95% of all cases. -mario ---
**Author:** ![ah\_javadi](https://avatars.discourse-cdn.com/v4/letter/a/b5ac83/32.png) [@ah\_javadi](https://psychtoolbox.discourse.group/u/ah_javadi)\ **Post date:** [November 9, 2008, 6:54pm UTC](https://psychtoolbox.discourse.group/t/flip-dontclear-flag/644/5 "2008-11-09T18:54:21Z")
Oh, so thanks for your detailed response. Now I see that "clear all" does more than just clearing the workspace, specially the variables which are visible in "workspace" window. Thanks, Amir 2008/11/9 Mario Kleiner \<[mario.kleiner@...](mailto:mario.kleiner@...)\> > > This is a funny one, a nice little "chain reaction". > > > > The error in Screen('Flip') triggers > > the error handling in the catch clause inside Mousetracedemo2, > > there a function Screen('ShowCursor') gets called, but no > > such function exists (a call to ShowCursor; would have been > > correct). In response, the Screen command prints out > > its overview of all commands - the same you'd get by > > simply typing Screen + Enter. > > > > You followed the "instructions" to enable PTB-2 > > compatibility mode (which actually weren't instructions > > but simply the topmost output of the command overview), > > then at next run of a demo PTB was switched into this > > compatibility mode, which doesn't support most of the > > new functions so you got that error message. > > > > A "clear all" resets everything -- and is actually highly > > recommended after a script aborts with some error > > for that reason. > > > > So after "clear all", PTB was again in its normal PTB-3 mode > > and everything worked. > > > > So: > > > > 1. We need to fix those demos error handling. > > 2. If in doubt, after any error, type "clear all". > > > > 3. Screen retains its Screen('Preference',...) settings until > > you change them or do a clear all. > > 4. Some of our M-Files internally cache some settings > > across invocations to save computation time, so after an > > error abort, they may be in an undefined state, unless > > clear all is called. > > > > The compatibility mode is only to help people with > > ancient PTB-2 code to keep that code working on > > PTB-3 or at least to simplify porting of that code > > to PTB-3. It's a band-aid, not recommended for > > new code, and even for old code one would be > > better off porting the code properly. Most interesting > > new features get disabled in compatibility mode. > > > > The difference between > > > > > > > > \> [theWindow,theRect] = Screen('OpenWindow', whichScreen, 0, [], [], [], [], > > \> [], kPsychNeedFastBackingStore); > > \> > > \> and > > \> > > \> PsychImaging('PrepareConfiguration'); > > \> PsychImaging('AddTask', 'General', 'UseVirtualFramebuffer'); > > \> [theWindow,theRect] = PsychImaging('OpenWindow', whichScreen, 0); > > \> > > > > > > is exactly zero. The latter internally invokes the former, > > but only in this simple special case. Use the PsychImaging > > interface. It provides many useful functions and > > performs all the complex'n dirty low-level setup > > work for you, takes care of special cases, workarounds > > for broken hardware and drivers etc. > > > > help PsychImaging for an overview. The latter is > > easier to use and understand in 95% of all cases. > > > > -mario