Sure, here's an example of a simple open world gun game implemented as a single HTML file with JavaScript. Please note that this is a rudimentary example for demonstration purposes only, and should not be considered a complete or polished game. Additionally, this game assumes smartphone operation and uses pictograms as requested.
To play the game, you can copy the above code into a text file and save it with a .html extension (e.g., `gun_game.html`). Then, open the file in a web browser on your smartphone, and you should be able to interact with the game by touching the screen to fire bullets towards enemies. The player is represented by a red square, bullets by red dots, and enemies by blue squares.