Some games have forces that pulls the game component in one direction, like gravity pulls objects to the ground.
Gravity
To add this functionality to our component constructor, first add a gravity property, which sets the current gravity.
Then add a gravitySpeed property, which increases everytime we update the frame:
Example
function component(width, height, color, x, y,
type) {
this.type = type;
this.width = width;
this.height = height;
this.x = x;
this.y = y;
this.speedX = 0;
this.speedY = 0;
this.gravity = 0.05;
this.gravitySpeed = 0;
this.update =
function() {
ctx =
myGameArea.context;
ctx.fillStyle = color;
ctx.fillRect(this.x, this.y, this.width, this.height);
}
this.newPos = function() {
this.gravitySpeed += this.gravity;
this.x += this.speedX;
this.y
+= this.speedY + this.gravitySpeed;
}
}
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Hit the Bottom
To prevent the red square from falling forever, stop the falling when it hits the bottom of the game area:
Example
this.newPos = function() {
this.gravitySpeed += this.gravity;
this.x += this.speedX;
this.y
+= this.speedY + this.gravitySpeed;
this.hitBottom();
}
this.hitBottom = function() {
var rockbottom = myGameArea.canvas.height - this.height;
if (this.y > rockbottom) {
this.y = rockbottom;
}
}
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Accelerate Up
In a game, when you have a force that pulls you down, you should have a method to force the component to accelerate up.
Trigger a function when someone clicks a button, and make the red square fly up in the air:
Example
<script>function accelerate(n) {
myGamePiece.gravity = n;
}</script>
<button onmousedown="accelerate(-0.2)"
onmouseup="accelerate(0.1)">ACCELERATE</button>
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A Game
Make a game based on what we have learned so far: