Spritesheets and Why You Should Use Them
Now that you understand basic sprites, it's time to talk about a better way to create them - the Spritesheet class.
A Spritesheet is a media format for more efficiently downloading and rendering Sprites. While somewhat more complex to create and use, they are a key tool in optimizing your project.
Anatomy of a Spritesheet
The basic idea of a spritesheet is to pack a series of images together into a single image, track where each source image ends up, and use that combined image as a shared BaseTexture for the resulting Sprites.
The first step is to collect the images you want to combine. The sprite packer then collects the images, and creates a new combined image.
As this image is being created, the tool building it keeps track of the location of the rectangle where each source image is stored. It then writes out a JSON file with that information.
These two files, in combination, can be passed into a SpriteSheet constructor. The SpriteSheet object then parses the JSON, and creates a series of Texture objects, one for each source image, setting the source rectangle for each based on the JSON data. Each texture uses the same shared BaseTexture as its source.
SpriteSheets help your project in two ways.
First, by speeding up the loading process. While downloading a SpriteSheet's texture requires moving the same (or even slightly more!) number of bytes, they're grouped into a single file. This means that the user's browser can request and download far fewer files for the same number of Sprites. The number of files itself is a key driver of download speed, because each request requires a round-trip to the webserver, and browsers are limited to how many files they can download simultaneously. Converting a project from individual source images to shared sprite sheets can cut your download time in half, at no cost in quality.
Second, by improving batch rendering. WebGL rendering speed scales roughly with the number of draw calls made. Batching multiple Sprites, etc. into a single draw call is the main secret to how PixiJS can run so blazingly fast. Maximizing batching is a complex topic, but when multiple Sprites all share a common BaseTexture, it makes it more likely that they can be batched together and rendered in a single call.
You will need to use a 3rd party tool to assemble your sprite sheet files. Here are two that may fit your needs:
ShoeBox: ShoeBox is a free, Adobe AIR-based sprite packing utility that is great for small projects or learning how SpriteSheets work.
TexturePacker: TexturePacker is a more polished paid tool that supports advanced features and workflows. It's a good fit for larger projects and professional game development.