game-engine/modules/game-objects/camera.js

import { GAME_HEIGHT, GAME_WIDTH, TILE_SIZE } from "../constants.js";
import { GameObject } from "./game-object.js";

export class Camera extends GameObject {
  constructor({
    gameObjects = [],
    x = 0,
    y = 0,
    width = GAME_WIDTH,
    height = GAME_HEIGHT,
    speed = 1,
    target = { x: 0, y: 0, width: 0, height: 0 }, // A camera that follows a target
  }) {
    super({ x, y, gameObjects, width, height });
    this.speed = speed;
    this.target = target;
    this.eventEmitter.on("levelChanged", () => {
      this.x = x;
      this.y = y;
    });
    this.eventEmitter.on("targetChanged", (target) => {
      this.target = target;
    });
  }

  update(delta) {
    super.update(delta);
    this.followTarget();
  }

  render(ctx) {
    this.gameObjects.forEach((item) =>
      item.render(ctx, this.x, this.y, this.width, this.height)
    );
  }

  followTarget() {
    const { x, y, width: tWidth, height: tHeight } = this.target;
    const centerX = x + tWidth / 2;
    const centerY = y + tHeight / 2;
    const [item] = this.gameObjects;
    const { height, width } = item.selected ?? item;
    this.x = Math.max(
      0,
      Math.min(centerX - this.width / 2, width * TILE_SIZE - this.width)
    );
    this.y = Math.max(
      0,
      Math.min(centerY - this.height / 2, height * TILE_SIZE - this.height)
    );
  }
}