meteor.js

MeteorImg = new Image();
MeteorImg.src = 'images/meteor.png'
meteors = new Array()
PlanetImg = new Image();
PlanetImg.src = 'images/planet.png'

function Meteor(canvasCtx, space, type, prevX){
    this.canvasCtx = canvasCtx
    this.xPos = 0;
    this.yPos = 0;
    this.dX = 0;
    this.dY = 0;
    this.type = type;
    this.prevX = prevX;

    this.planetSize = 60;

    this.nImage = 0;
    this.imgWidth = 40;
    this.imgHeight = 60;

    this.frameCount = 0;
    this.frameLoopCycle = 15;
    this.space = space;
    this.init()
}

Meteor.prototype = {
    init: function() {
        this.imgSprite = MeteorImg;

        //prevent 2 meteors from spawning together and make spawn distribution pseudo triangular with mean at center
        while (Math.abs(this.xPos - this.prevX) < 25 || this.xPos == 0) {
            this.xPos = Math.floor(Math.random() * (this.canvasCtx.canvas.width - 10) + 5);
            var xBias = Math.random() * (this.canvasCtx.canvas.width/4);
            this.xPos += this.xPos > this.canvasCtx.canvas.width/2 ? -xBias : xBias;
        }  

        this.yPos = -this.imgSprite.height - 10; // Meteor should start off of the screen
        this.radius = this.imgWidth/4;
        this.dX = 0;
        switch (this.type) {
            case -2:
                this.dY = 2.5;
                this.xPos = this.space.Game.Player.charX - 10 + Math.random() * 20;
                break;
            case -1:
                this.dY = 2.5;
                this.xPos = this.space.Game.Player.charX;
                break;
            case 0:
                this.dY = 2.5;
                break;
            case 1:
                this.dY = 4;
                break;
            case 2:
                this.dY = 5.5;
                break;
            case 3:
                this.dX = Math.random() > 0.5 ? -1.0 : 1.0;
                this.dY = 4;
                break;
            case 4:
                this.dY = 5.5;
                this.xPos = this.space.Game.Player.charX - 10 + Math.random() * 40;
                break;
            case 5:
                this.dX = Math.random() > 0.5 ? -1.5 : 1.5;
                this.dY = 4;
                this.xPos = this.space.Game.Player.charX - 10 + Math.random() * 40;
                break;
        }
        this.draw();
        meteors.push(this);
    },
    
    draw: function() {
        this.canvasCtx.drawImage(MeteorImg, this.nImage * this.imgWidth, 0, this.imgWidth, this.imgHeight, this.xPos, this.yPos, this.imgWidth, this.imgHeight);
        if (this.frameCount % this.frameLoopCycle == 0) {
            this.nImage++;
        }
        if (this.nImage > 3) {
            this.nImage = 0;
        }
    },

    update: function(frameCount) {
        this.frameCount = frameCount
        if(inCtxBounds(this.imgSprite, this.xPos, this.yPos, this.canvasCtx)){
            this.xPos += this.dX
            this.yPos += this.dY
            this.draw()
        } else {
            this.space.removeMeteor(this);
        }
    }
}

function inCtxBounds(img, x, y, ctx){
    return x > 0 - img.width && x < ctx.canvas.width + img.width
        && y < ctx.canvas.height + img.height;
}