Fix PyrenderViewer black screen on macOS (#630)

On macOS, pyglet.app.run() is not called, so the scheduled
enable_rendering callback was never executed. This caused
_allow_rendering to remain False, making on_draw() return
early without rendering anything.

Enable rendering directly for macOS instead of scheduling it.

Author: iory

skrobot/viewers/_pyrender.py

@@ -218,9 +218,12 @@ def _init_and_start_app(self):
         def enable_rendering(dt):
             self._allow_rendering = True
 
-        clock.schedule_once(enable_rendering, 0.1)
-
-        if compat_platform != 'darwin':
+        if compat_platform == 'darwin':
+            # On macOS, pyglet.app.run() is not called, so we enable rendering directly
+            # after a short delay via multiple redraw cycles in show()
+            self._allow_rendering = True
+        else:
+            clock.schedule_once(enable_rendering, 0.1)
             pyglet.app.run()
 
     def redraw(self):