sokol_app.h: initial mouse position on macos.

Send an initial mouse move event just after init and before the first frame. That allows the app to know where the mouse is before mouse is actually moved.

sokol_app.h

@@ -3299,6 +3299,17 @@ _SOKOL_PRIVATE void _sapp_frame(void) {
     if (_sapp.first_frame) {
         _sapp.first_frame = false;
         _sapp_call_init();
+
+        // Send an initial mouse move event so the app knows where the cursor is
+        // before the mouse is actually moved.
+        // NOTE: This must be done after calling the app's init callback, because
+        // the app might want to initialize whatever will recieve the sokol events
+        // (e.g. dearimgui) in init. It must be done before the first frame_cb call
+        // so there is no frame in which the app doesn't know the mouse position.
+        if (_sapp_events_enabled()) {
+            _sapp_init_event(SAPP_EVENTTYPE_MOUSE_MOVE);
+            _sapp_call_event(&_sapp.event);
+        }
     }
     _sapp_call_frame();
     _sapp.frame_count++;
@@ -4075,6 +4086,10 @@ _SOKOL_PRIVATE void _sapp_macos_frame(void) {
         data1:0
         data2:0];
     [NSApp postEvent:focusevent atStart:YES];
+
+    // Update the mouse position so the app knows where the cursor is before the
+    // mouse is actually moved. An event is sent in _sapp_frame. 
+    _sapp_macos_mouse_update_from_nspoint([_sapp.macos.window mouseLocationOutsideOfEventStream], true);
 }
 
 - (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication*)sender {