Game Component: Sprite

A basic sprite component for use in 2d games, with animations and directions.

Installation

npm install @basementuniverse/sprite

For direct browser usage, include the UMD build with a script tag:

<script src="build/index.js"></script>

The build exposes its exports through the BasementUniverseSprite browser namespace. It does not add each export directly to window.

How to use

Create a sprite:

import { Sprite } from '@basementuniverse/sprite';

const sprite = new Sprite({
  // options here...
});

When using the library directly from a browser script, prefix exports with BasementUniverseSprite:

<script src="build/index.js"></script>
<script>
  const sprite = new BasementUniverseSprite.Sprite({
    // options here...
  });
</script>

Update the sprite every frame:

sprite.update(dt);

Set the sprite's properties at any time:

sprite.position = vec(100, 100);
sprite.scale = 1;
sprite.rotation = 0; // radians

(see here for vec library)

Get or set the sprite's direction and animation:

sprite.animation = 'walk';
sprite.direction = 'right';

Start/pause/reset the current animation:

sprite.playAnimation();
sprite.pauseAnimation();
sprite.resetAnimation();

Render the sprite every frame:

sprite.draw(context);

Get the image for the current frame:

sprite.image; // the image that draw() will use, updated by sprite.update()

Get the same frame for another direction, without changing the sprite's direction:

sprite.getImage('left');

Get an image from one of the animation's layers:

sprite.getImage(sprite.direction, 'normal');

Options

export type SpriteOptions = {
  /**
   * The position of the sprite
   *
   * Defaults to (0, 0)
   */
  position?: vec;

  /**
   * The base size of the sprite
   *
   * If omitted, use the base image size, or fall back to the size of the
   * first image found in available directions for the default animation
   *
   * If a size still can't be found, default to (0, 0)
   */
  size?: vec;

  /**
   * Origin offset from top-left corner, used for rotation and scaling
   *
   * If omitted, this will be placed in the center of the sprite (based on
   * size, noting that size will be calculated first)
   *
   * @see SpriteOptions.size
   */
  origin?: vec;

  /**
   * The scale factor of the sprite
   *
   * Default is 1
   */
  scale?: number;

  /**
   * The sprite rotation, measured in radians
   *
   * Default is 0
   */
  rotation?: number;

  /**
   * An array of valid direction names
   *
   * By default a sprite will have one available direction: 'default'
   */
  directions: string[];

  /**
   * The initial direction of the sprite
   *
   * Default is 'default'
   */
  defaultDirection: string;

  /**
   * An optional base image
   *
   * If an animation frame doesn't exist (for example an animation has been
   * configured with 5 frames but only 3 images exist in the animation's
   * images array), we fall back to this image
   *
   * If an animation frame image can't be found and this base image doesn't
   * exist, we can still render the sprite - it will just have an empty image
   *
   * (this can be useful for sprites that act purely as hosts for attachment
   * points, for example)
   */
  image?: HTMLImageElement | HTMLCanvasElement;

  /**
   * A dictionary of animations
   *
   * Each animation can have multiple variants for different directions
   *
   * Use '*' as a direction name to indicate that a variant is available for
   * all directions and can be used as a fallback if the current direction
   * can't be found
   */
  animations: {
    [name: string]: {
      [direction: string]: SpriteAnimationOptions;
    };
  };

  /**
   * The initial animation for the sprite
   */
  defaultAnimation: string;

  /**
   * A list of attachment points
   */
  attachmentPoints?: SpriteAttachmentPointOptions[];

  /**
   * Optional hook called before rendering the sprite image
   */
  preRender?: (
    context: CanvasRenderingContext2D,
    sprite: Sprite
  ) => void;

  /**
   * Optional hook called after rendering the sprite image
   */
  postRender?: (
    context: CanvasRenderingContext2D,
    sprite: Sprite
  ) => void;

  /**
   * Optional debug options
   *
   * Can be a boolean value (in which case all sub-options will be set to the
   * same value), or an object allowing specific debug options to be enabled
   * individually
   */
  debug?: Partial<SpriteDebugOptions> | boolean;
};

export type SpriteAnimationOptions = {
  /**
   * The name of this animation
   */
  name: string;

  /**
   * The number of frames in this animation
   */
  frameCount: number;

  /**
   * The number of frames per second when playing this animation
   */
  frameRate: number;

  /**
   * The repeat mode for this animation
   */
  mode: SpriteAnimationRepeatMode;

  /**
   * A list of images to use for each frame
   *
   * If this list is longer than frameCount, some images won't be used
   *
   * If this list if shorter than frameCount, we fall back to the base image
   * or don't show an image for some frames
   */
  images?: (HTMLImageElement | HTMLCanvasElement)[];

  /**
   * Named lists of extra images to go with each frame, for example normal maps
   *
   * These aren't drawn by the sprite, use `getImage()` to read them. Unlike
   * `images` there's no fallback to the base image, if a layer doesn't have an
   * image for a frame then `getImage()` will return null
   */
  layers?: {
    [layerName: string]: (HTMLImageElement | HTMLCanvasElement)[];
  };

  /**
   * Keyframes for attachment points
   */
  attachmentPointKeyframes?: {
    [attachmentPointName: string]: SpriteAttachmentPointKeyframe[];
  };
};

(see build/index.d.ts for more details)

Attachment points

Sprites can have multiple named attachment points. These attachment points can be given a default position, and the position can be modified via animation keyframes in each animation.

Fetch an attachment point by name:

sprite.getAttachmentPoint('weapon-left-hand');
// returns a vec: { x: number; y: number } or null

This could be useful for connecting multiple sprites together.

Content processor

A content processor function is provided for use with the Content Manager.

import { spriteOptionsContentProcessor } from '@basementuniverse/sprite';

This function will take a JSON object resembling the SpriteOptions type (see below for an explanation of differences) and return a SpriteOptions object which can be passed into the Sprite constructor.

• The JSON object may have an imageName: string field instead of image. The image name will be used to fetch the image from the content manager, and the imageName field will then be replaced with an image field, containing the fetched image.

• Similarly, the JSON object may have an imageNames: string[] field instead of images in each animation. These images will be loaded from the content manager and the imageNames field will be replaced with an images field, containing the fetched images.

• Each animation may also have a layerImageNames: { [layerName: string]: string[] } field instead of layers, which is converted in the same way.