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);
}
}
}
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Change Images
You can change the image whenever you like by changing the src
property of the image
object of your component.
![](smiley.gif)
![](angry.gif)
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;
}
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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();
}
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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();
}
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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;
}
}
}
}
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