commit 87475c20d6cc81912e58f21369b101271d4732f6
Author:     Albrecht Schlosser <albrechts.fltk@online.de>
AuthorDate: Wed Jul 7 15:35:14 2021 +0200
Commit:     Albrecht Schlosser <albrechts.fltk@online.de>
CommitDate: Wed Jul 7 15:35:14 2021 +0200

    macOS: Fix a timer inconsistency and prevent a crash
    
    Calling Fl::repeat_timeout() instead of Fl::add_timeout() to create
    a timer would crash on macOS but fall back to Fl::add_timeout() on
    Windows and Unix/Linux. Although this is documented as "undefined
    behavior" a crash should always be avoided and the fallback is now
    consistent on all major platforms.
    
    In the future this may be documented as the standard behavior.

 src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx | 4 ++++
 1 file changed, 4 insertions(+)

diff --git src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
index 1838a73..2caf174 100644
--- src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
+++ src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
@@ -518,6 +518,10 @@ void Fl_Cocoa_Screen_Driver::add_timeout(double time, Fl_Timeout_Handler cb, voi
 
 void Fl_Cocoa_Screen_Driver::repeat_timeout(double time, Fl_Timeout_Handler cb, void* data)
 {
+  if (!current_timer) {
+    add_timeout(time, cb, data);
+    return;
+  }
   // k = how many times 'time' seconds after the last scheduled timeout until the future
   double k = ceil( (CFAbsoluteTimeGetCurrent() - current_timer->next_timeout) / time);
   if (k < 1) k = 1;