2018js13k/camera.js

function Camera() {
	this.position = {x: -100, y: -100};	
	this.viewBox = {x: 100, y: 100, width: 600, height: 400};

	this.init = function(canvas) {
		this.viewBox.x = canvas.width / 3;
		this.viewBox.y = canvas.height / 3;
		this.viewBox.width = canvas.width - 2 * this.viewBox.x;
		this.viewBox.height = canvas.height - 2 * this.viewBox.y;

		this.position = {x: canvas.width / 2, y: canvas.height / 2};	
	}
	
	this.update = function(canvas, player, delta) {
		this.followPlayer(player, delta);
	}

	this.handleResize = function(canvas) {
		this.viewBox.x = canvas.width / 3;
		this.viewBox.y = canvas.height / 3;
		this.viewBox.width = canvas.width - 2 * this.viewBox.x;
		this.viewBox.height = canvas.height - 2 * this.viewBox.y;
	}

	this.followPlayer = function(player) {
		var truePos = {x: 0, y: 0};
		truePos.x = this.position.x + player.position.x;
		truePos.y = this.position.y + player.position.y;

		if(truePos.x <= this.viewBox.x) {
			this.position.x -= truePos.x - this.viewBox.x;
		}

		if(player.position.x + this.position.x >= this.viewBox.x + this.viewBox.width) {
			this.position.x += (this.viewBox.x + this.viewBox.width) - truePos.x;
		}

		if(truePos.y <= this.viewBox.y) {
			this.position.y -= truePos.y - this.viewBox.y;
		}

		if(player.position.y + this.position.y >= this.viewBox.y + this.viewBox.height) {
			this.position.y += (this.viewBox.y + this.viewBox.height) - truePos.y;
		}
	}
};