FtWorker

FtWorker is the analysis-pipeline class that converts Fid objects into Ft magnitude spectra. Three slot methods cover the three usage patterns: doFT() for a single FT, doFtDiff() for the difference between two spectra, and processSideband() for the incremental LO-scan stitching that builds a broadband spectrum from a series of per-LO-step FTs. Each slot is invoked through QtConcurrent::run rather than via a dedicated QThread; results are returned both by signal (ftDone, ftDiffDone, sidebandDone) and as the slot’s return value, so the same instance serves both the asynchronous UI path (FtmwViewWidget) and the synchronous batch path (BatchManager).

The transform itself uses the GSL mixed-radix real FFT, which is most efficient when the FID length factors into powers of 2, 3, and 5. The frequency-domain plot, peak finder, and overlay system in both blackchirp and the blackchirp-viewer consume the resulting Ft via ExperimentViewWidget; the user-facing controls that drive FidProcessingSettings are described in Data Storage and the FT-domain UI documentation.

Preprocessing pipeline

Before the FFT, FtWorker applies an optional pipeline of time-domain steps driven by FidProcessingSettings:

Truncation to a sub-window via startUs / endUs.
DC removal (subtract the FID mean).
Exponential apodization (expFilter).
Zero-padding (zeroPadFactor).
Window-function apodization — one of FtWindowFunction: Bartlett, Blackman, Blackman-Harris, Hamming, Hanning, Kaiser-Bessel.

The magnitude scale of the output Ft is controlled by FidProcessingSettings::units. The enumeration values map directly to powers of ten relative to the digitized voltage: e.g. FtmV = 3 multiplies by 10³ / rawSize, so the spectrum reads in mV per FFT bin. The window-function cache is keyed on (window, length) and guarded by pu_winfLock so repeated FFTs at the same size pay the window cost only once.

Threading

FtWorker is a QObject but is not moved to a dedicated QThread. Callers invoke doFT(), doFtDiff(), and processSideband() through QtConcurrent::run, which schedules each call on the global thread pool. The signals ftDone, fidDone, ftDiffDone, and sidebandDone are emitted from the thread-pool thread, so connections to UI slots require queued delivery (the default when the receiver lives on a different thread). When called from a non-UI thread (e.g. a BatchManager), the return values of doFT() and filterFid() can be used directly without waiting for the signals. The id parameter of doFT() selects the path: pass id >= 0 to get signal delivery (asynchronous) or id = -1 to suppress signals (synchronous).

GSL workspace allocation is guarded by pu_fftLock and spline allocation by pu_splineLock, so the same FtWorker instance can be called concurrently from multiple thread-pool threads provided each concurrent call uses a different code path.

Resource management

GSL wavetables, workspaces, and spline objects are allocated lazily on first use and freed by the destructor. When idle-cleanup is enabled via setIdleCleanupEnabled(), resources are also freed automatically after a 5-minute inactivity timeout (cleanupResources()). Call resetIdleTimer() after each processing operation to restart the countdown.

API Reference

class FtWorker : public QObject

Processes Fid objects into magnitude spectra using the GNU Scientific Library FFT.

Not moved to a dedicated QThread: callers invoke doFT(), doFtDiff(), and processSideband() through QtConcurrent::run, so the ftDone / fidDone / ftDiffDone / sidebandDone signals are emitted on a thread-pool thread and require queued connections to UI slots. The id parameter of doFT() picks the path: id = -1 suppresses signals (synchronous use); id >= 0 emits async signals. Per-instance locks (pu_fftLock, pu_splineLock, pu_winfLock) allow concurrent calls on the same instance provided each call uses a different code path.

GSL wavetables, workspaces, and spline objects are allocated lazily on first use and freed by the destructor. When idle-cleanup is enabled via setIdleCleanupEnabled(), resources are also freed after a 5-minute inactivity timeout; resetIdleTimer() restarts the countdown after each processing operation.