An ATLAS file is a settings file created by Phaser Editor, an IDE used to develop HTML5 games. It is used to generate a texture atlas, which is a .PNG image packed with a collection of sprites that are used for textures of objects and characters in a game. ATLAS files contain the settings for a texture atlas and the paths to each sprite to be packed in the PNG image when the game is built.

You can open and edit ATLAS files in Phaser Editor. When you are finished editing the ATLAS file, you can generate the texture atlas. The texture atlas includes a PNG image with the sprite textures and a .JSON file, which contains the placement of each sprite in the PNG file. The JSON file is referenced by the game to apply the correct textures to each character or object in the game. Texture atlases are typically utilized to combine sprite textures for characters or objects in a game into one larger file. This feature reduces the number of separate sprite texture files. Instead of using multiple images to texture objects and characters, developers can use Phaser Editor or another framework to generate one PNG file with multiple sprites packed in it. The graphics hardware in the device running the game can treat the sprites as one unit instead of multiple units, which reduces the number of bind and draw calls and saves memory. Texture atlases may be created by a variety of 2D game frameworks, such as Photon Storm Phaser and Apple SpriteKit. Some games that use texture atlases, include Iron Armada, Surge Breaker, Goodnight, and Protolife. Although Phaser Editor uses ATLAS files to generate texture atlases, other frameworks, such as Photon Storm Phaser and Apple SpriteKit, do not use an ATLAS file. Instead, developers using these frameworks place sprites inside a folder with the .atlas extension and the framework generates the PNG texture atlas and JSON or .XML file when the game is built.