Hi, you can also use the built in shapes (rectangle and circle) to act as buttons, you just add the same triggers you have on the buttons to the specific shape. Regarding the triangle, you can use a vector triangle image and add the button triggers to it.
If you want to simulate the pressed actions on the buttons (like pressed image & release image) you would need to add those as separate actions in the triggers. This is an extra step but then you’d be free to use anything to work like a button and not be limited to the square buttons.
Melvin is right about the circle workaround but I’m afraid this won’t work for the triangle. The only way to integrate vectorial content is through the HTML asset which, as the button, has a rectangular container.
Your request is pretty similar to this one so I encourage you to add your scenario there and vote for it.