Sure! Here's an example of a simple 3D FPS game implemented as a single HTML file using JavaScript and enclosed within script tags. Please note that this is a simplified version and may not have all the features of a real game. You can play it by opening the HTML file in a web browser.
In this game, you control a blue circle representing the player. The player can be moved by handling input events such as touch events. The `gameLoop` function continuously updates the player's position and re-renders the canvas to create the illusion of motion. This is a basic foundation for a 3D FPS game, and you can expand upon it to add more features like enemies, shooting mechanics, and level design.