When you want a sprite to respond to mouse or touch input in PixiJS, you must set its interactive property to true. This tells PixiJS to listen for pointer events on that sprite. Once a sprite is interactive, you can use event listeners such as pointerdown, pointerup, pointermove, and others to respond to user actions.

Events in PixiJS follow a bubbling model similar to web browsers. If a sprite is inside a container, and both the sprite and the container are interactive, an event like pointerdown on the sprite will also bubble up to the container unless you stop its propagation. You can use the event.stopPropagation() method inside your event handler if you want to prevent the event from reaching parent containers.

Here are some practical tips for sprite interactivity:

• Always set interactive = true on any display object you want to receive pointer events;
• Make sure the sprite is added to the stage or a visible container;
• If you want the sprite to show a pointer cursor when hovered, set buttonMode = true;
• Use .on() to add event listeners, and .off() to remove them when no longer needed;
• Remember to consider event bubbling if you have nested containers or sprites.

With these practices, you can create buttons, draggable objects, or any interactive elements for your game.