Game Gravity
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;
}
}
Try it Yourself »
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;
}
}
Try it Yourself »
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>
Try it Yourself »
A Game
Make a game based on what we have learned so far:
