hm.
with macos i am getting only “0” on most browsers ( Safari, Firefox, Chrome ) Only Waterfox 56.3 gives me “2” when ctrl-clicking.
On Windows only Edge gives me “2” when alt-clicking.
buttonIndex is the mouse button used for clicking (0 = left click, 1 = middle button, 2 = right button), this has nothing to do with ctrl/shift/alt key pressed while clicking. I checked on Windows (FF, Chrome, Edge) and Mac (Safari). All behave the same. Maybe I’m missing the same.
If you want to check keyboard key pressed while clicking, you can check Events handling Event Handling - Babylon.js Documentation
I don’t know if there is a better/simpler way to check the key pressed.