UI API called on a background thread

[Crazor]

There appears to be an issue with UI calls from the wrong thread, as reported while debugging in Xcode:

2021-05-09 12:56:31.360310+0200 Jitouch[18870:500720] [reports] Main Thread Checker: UI API called on a background thread: -[NSView setNeedsDisplay:]
PID: 18870, TID: 500720, Thread name: (none), Queue name: com.apple.root.default-qos.overcommit, QoS: 0
Backtrace:
4   Jitouch                             0x000000010000c824 -[GestureWindow refresh] + 52
5   Jitouch                             0x000000010000c87b -[GestureWindow setHintText:] + 75
6   Jitouch                             0x000000010001ae5d trackpadRecognizerTwo + 1037
7   Jitouch                             0x000000010000d0ea trackpadCallback + 314
8   MultitouchSupport                   0x00007fff59400bd2 MTAlg_IssueContactFrameCallbacks + 171
9   MultitouchSupport                   0x00007fff593fb22d mt_HandleMultitouchFrame + 2251
10  MultitouchSupport                   0x00007fff593f98c8 mt_DequeueMultitouchDataMachPortCallBack + 140
11  CoreFoundation                      0x00007fff322fbb2b __CFMachPortPerform + 288
12  CoreFoundation                      0x00007fff322cd304 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41
13  CoreFoundation                      0x00007fff322cd250 __CFRunLoopDoSource1 + 541
14  CoreFoundation                      0x00007fff322cbd79 __CFRunLoopRun + 2270
15  CoreFoundation                      0x00007fff322cae3e CFRunLoopRunSpecific + 462
16  CoreFoundation                      0x00007fff32353489 CFRunLoopRun + 40
17  MultitouchSupport                   0x00007fff593f49c6 mt_ThreadedMTEntry + 71
18  libsystem_pthread.dylib             0x0000000100454c65 _pthread_start + 148
19  libsystem_pthread.dylib             0x00000001004504af thread_start + 15