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.
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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