Psychtoolbox release “Virtuality!” SP4 released

Psychtoolbox 3.0.19 Beta update “Virtuality” SP4 was released at 27th October 2023.
As usual, the complete development history can be found in our GitHub repository.
The release tag is “”, with the full tree and commit logs under the URL:

This Psychtoolbox release was partially sponsored by Mathworks under the year
2023/2024 contract.

Compatibility changes wrt. Psychtoolbox

  • On MS-Windows, GStreamer 1.22 is now required, the latest lightly tested
    version is GStreamer 1.22.5. With the older GStreamer 1.20, text rendering
    with the high quality drawtext plugin will no longer work, and the fallback
    GDI text renderer would be used, which is officially unsupported in case of
    trouble and has lower performance/quality/features/reliability.

  • On macOS if using Octave, Octave 8.3 is now recommended and tested, but older
    Octave versions back to v6.3 are expected (but not tested) to continue to work.


None, just a large grab bag of various minor and major fixes and improvements.


  • Some Unix file permission cleanup contributed by Yaroslav from NeuroDebian.

  • CalibrateMonSpd(): Fix some fallout from previous fixes. Set cal.describe.dacsize
    also if g_usebitspp is already set. Reference:

  • DegreesToRetinalEccentricityMM(): Fix typo in code that prevented replacement
    of small angles by the linear approximation. Contributed by Stella Prins.

  • MakeSineImage(): Allow passing of center (0 phase) position of the sinusoid.
    Contributed by David Brainard.

  • ComputePhotopigmentBleaching(): Add constants from Wyszecki and Stiles.
    Contributed by David Brainard.

  • New touchscreen demo: MultiTouchPinchDemo.m, to show detection and handling of
    two finger pinch gestures on touchscreens.

  • Output info message with potential troubleshooting tips if drawtext init takes
    unusually long, hinting at potential fontconfig cache rebuild (problems) on
    MS-Windows. May or may not help anybody, but probably doesn’t hurt. Suggested
    by GitHub user @mirh.

  • DrawFormattedText(): Add new keyword ‘left’ to use for the ‘sx’ parameter. It
    will left-align drawn text to the left border of an optionally provided
    ‘winRect’, similar to the ‘right’ keyword for right-alignment. Improvement
    contributed by GitHub user @SVNKoch.

  • PsychPortAudio: Add potential workaround to deal with temperamental / weird
    audio sound cards. Add a new optional parameter to the tweaking command
    PsychPortAudio('EngineTunables', ...., workarounds);, which allows to
    specify a non-default (ie. non-zero) workarounds bitmask to selectively
    disable or enable workarounds. The currently defined workaround bits are the
    following, which modify how the Portaudio audio format test function
    Pa_IsFormatSupported is handled:

    +1 = Do not error abort on test failure, ie. print warnings but don’t abort.
    +2 = Skip the whole test and always assume success.

    Both could help if the test reports false positives (+1 to continue), or
    if some hardware queries/operations themselves during the test trigger
    some trouble (+2 to skip the whole test).

    Also various other minor improvements to PsychPortAudio and some of the audio
    demos and tests.

  • Snd(): Switch fallback method from use of sound() to use of audioplayer().
    Both modern Octave and Matlab implement sound() as a wrapper around their
    audioplayer() objects, so using audioplayer() directly gives us more control
    for a better Snd() fallback implementation. Also use the fallback method as
    new default by default. Iow. unless specified otherwise, Snd() will play
    via audioplayer(). This provides good interop with other audio clients and
    with Screen()'s GStreamer based movie playback engine.

  • Beeper(): Formatting/Indentation fixes, refine soundvector calculation.

  • BitsPlusIdentityClutTest: Disable encoder test if Vulkan display is used.
    Current design lead to the tests running before the Vulkan backend is fully
    in charge, so we display the PTB welcome screen or pixeltrash during the test,
    instead of the test stims, which leads to false-positive test failure. Just
    don’t offer the test option under Vulkan. DatapixxGPUDitherpatternTest is an
    alternative working way to test with Vulkan at the moment.

  • PsychOpenHMDVR: Use correct ipd/2 instead of ipd for warp-mesh setup in our
    OpenHMD driver.

  • Minor bug fixes, documentation updates and improvements.


  • Psychtoolbox was built and lightly tested against Matlab R2022b.

  • RPiGPIOMex: Various bug fixes and improvements. Also merged two alternative
    implementations of the file co-written by Steve Van Hooser and myself. These
    reimplement functionality by using the pigpio library instead of the old and
    deprecated wiringPi library. This should be more future-proof and maintainable.
    For now, the original file based on wiringPi is still used though, until we
    decide which of the two new variants is the better choice.

  • Fix exception handling on Octave for RaspberryPi on RaspberryPi OS, so errors
    only abort the users script and don’t terminate the whole Octave application.


  • Psychtoolbox was built and lightly tested against Matlab R2022b.

  • GStreamer 1.22 is now required, GStreamer 1.20 will have limitations.

  • Fix drawtext plugin again, so it no longer breaks under Matlab with
    GStreamer 1.22 on some systems. This will now require the installation
    of GStreamer 1.22, the older GStreamer 1.20 will no longer work with
    the drawtext plugin.

  • Windows: Remove support for building 32-Bit mex files.
    Matlab is 64-Bit only since a long time on Windows, Octave is about to
    remove 32-Bit support as well. Windows-10 - the last MS 32-Bit operating
    system is on the way to final retirement. Ergo, no need for 32-Bit builds
    in the future anymore.

  • Make Screen(‘Openwindow’) timing startup tests and calibrations more
    robust. This by disabling processor idling during the tests, ie. ACPI
    C-State processor power management transitions out of C0 (active). Such
    transitions can induce latency / variability in code execution timing bad
    enough to affect timing tests on some setups. If and how much this helps
    in practice remains to be seen. Based on investigations / measurements
    by GitHub user @mirh, see GitHub isse #793 for reference. If this new
    optimization causes trouble or interop problems with cpu performance
    tweaking tools, e.g., the Windows tools “throttlestop”, it can be disabled
    by use of the command before the first time you try to open an onscreen
    window in your experiment script:

    PsychTweak('DontDisableProcessorIdling', 1);


  • Psychtoolbox was built and lightly tested against Matlab R2022b and
    Octave 8.3 from HomeBrew.

  • Screen(): Add iMac20,1 and iMac20,2 aka year 2020 iMacs to timing fixup lut,
    so the visual timing fixes also apply to these final Intel iMac models with
    AMD Navi graphics chips. As the PsychtoolboxKernelDriver does not support AMD
    Navi graphics, our visual timestamping and our diagnostic for visual timing
    problems on these machines will be more limited than on older machines, but
    the untested expectation is that this should fix timing on 2020 iMac internal

  • Screen(): Remove conserveVRAM flag kPsychDontCacheTextures. It was useless and
    even buggy since years, so let it die.

  • Screen(): Add new conserveVRAM preference flag 2 == kPsychDontSwitchToOptimalVidMode.
    May or may not help fullscreen display on connected external video splitters like the
    Matrox DualHead2Go. This is based on a hunch, not on proper root causing. Cfe.
    Open window can't set to a specified rect size on macOS With Matrox Dualhead2Go


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