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Game Images


Push the buttons to move the smiley:








How to Use Images?

To add images on a canvas, the getContext("2d") object has built-in image properties and methods.

In our game, to create the gamepiece as an image, use the component constructor, but instead of referring to a color, you must refer to the url of the image. And you must tell the constructor that this component is of type "image":

Example

function startGame() {
  myGamePiece = new component(30, 30, "smiley.gif", 10, 120, "image");
  myGameArea.start();
}

In the component constructor we test if the component is of type "image", and create an image object by using the built-in "new Image()" object constructor. When we are ready to draw the image, we use the drawImage method instead of the fillRect method:

Example

function component(width, height, color, x, y, type) {
  this.type = type;
  if (type == "image") {
    this.image = new Image();
    this.image.src = color;
  }
  this.width = width;
  this.height = height;
  this.speedX = 0;
  this.speedY = 0;
  this.x = x;
  this.y = y;
  this.update = function() {
    ctx = myGameArea.context;
    if (type == "image") {
      ctx.drawImage(this.image,
        this.x,
        this.y,
        this.width, this.height);
    } else {
      ctx.fillStyle = color;
      ctx.fillRect(this.x, this.y, this.width, this.height);
    }
  }
}
Try it yourself »

Change Images

You can change the image whenever you like by changing the src property of the image object of your component.

If you want to change the smiley everytime it moves, change the image source when the user clicks a button, and back to normal when the button is not clicked:

Example

function move(dir) {
    myGamePiece.image.src = "angry.gif";
    if (dir == "up") {myGamePiece.speedY = -1; }
    if (dir == "down") {myGamePiece.speedY = 1; }
    if (dir == "left") {myGamePiece.speedX = -1; }
    if (dir == "right") {myGamePiece.speedX = 1; }
}

function clearmove() {
    myGamePiece.image.src = "smiley.gif";
    myGamePiece.speedX = 0;
    myGamePiece.speedY = 0;
}
Try it yourself »

Background Images

Add a background image to your game area by adding it as a component, and also update the background in every frame:

Example

var myGamePiece;
var myBackground;

function startGame() {
    myGamePiece = new component(30, 30, "smiley.gif", 10, 120, "image");
    myBackground = new component(656, 270, "citymarket.jpg", 0, 0, "image");
    myGameArea.start();
}

function updateGameArea() {
    myGameArea.clear();
    myBackground.newPos();
    myBackground.update();
    myGamePiece.newPos();
    myGamePiece.update();
}
Try it yourself »

Moving Background

Change the background component's speedX property to make the background move:

Example

function updateGameArea() {
    myGameArea.clear();
    myBackground.speedX = -1;
    myBackground.newPos();
    myBackground.update();
    myGamePiece.newPos();
    myGamePiece.update();
}
Try it yourself »

Background Loop

To make the same background loop forever, we must use a specific technique.

Start by telling the component constructor that this is a background. The component constructor will then add the image twice, placing the second image immediately after the first image.

In the newPos() method, check if the x position of the component has reach the end of the image, if it has, set the x position of the component to 0:

Example

function component(width, height, color, x, y, type) {
    this.type = type;
    if (type == "image" || type == "background") {
        this.image = new Image();
        this.image.src = color;
    }
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;
    this.x = x;
    this.y = y;
    this.update = function() {
        ctx = myGameArea.context;
        if (type == "image" || type == "background") {
            ctx.drawImage(this.image,
                this.x, this.y, this.width, this.height);
            if (type == "background") {
                ctx.drawImage(this.image,
                this.x + this.width, this.y, this.width, this.height);
            }
        } else {
            ctx.fillStyle = color;
            ctx.fillRect(this.x, this.y, this.width, this.height);
        }
    }
    this.newPos = function() {
        this.x += this.speedX;
        this.y += this.speedY;
        if (this.type == "background") {
            if (this.x == -(this.width)) {
                this.x = 0;
            }
        }
    }
}
Try it yourself »