I have completed a tutorial on how to create a simple brick breaker game in Javascript and now would like to expand on it. I have run into an issue of how to differentiate between a side/side collision and a top/bottom collision.
Right now, the collision detection function I have only checks if there has been a collision. Then in a separate class, if the collision function returns true, it negates the y coordinate of the trajectory, but not the x. So when the ball collides with either the top or bottom of a brick, it will change y directions which works, but if it collides with the side of a brick, it keeps traveling in the same x direction.
Here's the collision function:
export function objectCollision(ball, gameObject){
//Position of Ball
let topOfBall = ball.position.y;
let bottomOfBall = ball.position.y + ball.height;
let leftSideOfBall = ball.position.x;
let rightSideOfBall = ball.position.x + ball.width;
//Position of Object
let topOfObject = gameObject.position.y;
let bottomofObject = gameObject.position.y + gameObject.height;
let leftSideOfObject = gameObject.position.x;
let rightSideOfObject = gameObject.position.x + gameObject.width;
//Split up the top/bottom and left/right hit detection (causes abnormal behavior)
//Need to negate the x trajectory
//Set ball.speed.x = -ball.speed.x if left/right hit detection
if(bottomOfBall >= topOfObject && topOfBall <= bottomofObject && leftSideOfBall >= leftSideOfObject && rightSideOfBall <= rightSideOfObject){
//ball.speed.x = -ball.speed.x;
return true;
}
else
return false;
}
Then in the brick class, we change the y coordinate of the trajectory.
//Brick class
import { objectCollision } from "/src/collisionDetection"
export default class Brick{
//......
update(deltaTime){
if(objectCollision(this.game.ball, this)){
this.game.ball.speed.y = -this.game.ball.speed.y;
this.isHit = true;
}
}
//.....
}
My issue is that if I check for y coordinate collisions separate from the x coordinate collisions, it will detect a collision when the ball's x coordinate is the same as a brick's, even if the ball is lower/higher than the brick. I've tried checking for y's first and then in a nested if() check the x's, but it yielded the same result.
Something along the lines of:
if(bottomOfBall >= topOfObject && topOfBall <= bottomofObject && leftSideOfBall){
if(leftSideOfBall >= leftSideOfObject && rightSideOfBall <= rightSideOfObject){
ball.speed.x = -ball.speed.x;
return true;
}
}
But it gave the same abnormal behavior or broke collision all together.
Hopefully it's something simple that I'm just not seeing and an extra pair of eyes would fix. I really don't want to completely redo the collision detection.
Related
I realize this may be a common question however after looking at the other answers i'm not sure my implementation benefits from the answers.
My game has the player shooting from its X Y position towards the mouse X Y position, with the enemies falling linearly down the Y axis.
However it seems only the first shot or a random shot in on the screen will sometimes hit and remove an enemy, with some bullets passing straight through with a direct hit and not invoking the removal of the enemy.
The game can be seen here:
https://liammorgan.github.io/wave_defence/
And the snippet for hit detection is here, which works around 20% of the time, or on the first bullet shot.
Each shot has an X,Y,bulletSpeed, xVelocity, yVelocity
Each enemy has an X,Y,speed
shot.js -
this.hit = function() {
for(enemy in enemies) {
let e = enemies[enemy];
if(e != null) {
if(this.x+this.size > e.x && this.x-this.size < e.x &&
this.y+this.size > e.y && this.y-this.size < e.y) {
enemies[enemy] = null;
return true;
} else {
return false;
}
}
}
}
sketch.js -
let shots = [];
let enemies = [];
if(player.lives > 0) {
player.update();
player.draw();
for(shot in shots) {
let s = shots[shot];
if(s != null) {
if(s.hit() && s != null) {
shots[shot] = null;
continue;
}
shots[shot].update();
shots[shot].draw();
if(s.remove() && s != null) {
shots[shot] = null;
}
}
}
}
It seems to me that in your collision logic, you're not accounting for the size of the enemy itself. So for the collision to count, the shot has to PERFECTLY hit almost the exact center of the enemy.
A better way to do it would be to measure the distance from the center the bullet to the center of the enemy, and check that to their known sizes, since both the enemy and bullet are circles. This also means that you would have to include a radius or size field to the enemy objects.
So, I am currently reinventing the wheel (and learning a lot) by trying my hand at making a simple physics engine for my game engine. I have been searching the internet, trying (and failing) to fix my current problem. There are a lot of resources out there on the subject, but none of those that I have found seem to apply to my case.
THE PROBLEM IN SHORT: The collision resolution does not work as intended on some of the corners when two rectangles are colliding. How it fails varies based on the dimensions of the rectangles. What I am looking for is a "shortest overlap" kind of resolution for the collision or another fairly simple solution (I am open for suggestions!). (Scroll down for a better explaination and illustrations).
WARNING: The following code is probably not very efficient...
First of all, here is my physics loop. It simply loops through all of the game entities and checks if they collide with any other game entities. It is not efficient (n^2 and all of that), but it works for now.
updatePhysics: function(step) {
// Loop through entities and update positions based on velocities
for (var entityID in Vroom.entityList) {
var entity = Vroom.entityList[entityID];
if (entity.physicsEnabled) {
switch (entity.entityType) {
case VroomEntity.KINEMATIC:
entity.pos.x += entity.vel.x * step;
entity.pos.y += entity.vel.y * step;
break;
case VroomEntity.DYNAMIC:
// Dynamic stuff
break;
}
}
}
// Loop through entities and detect collisions. Resolve collisions as they are detected.
for (var entityID in Vroom.entityList) {
var entity = Vroom.entityList[entityID];
if (entity.physicsEnabled && entity.entityType !== VroomEntity.STATIC) {
for (var targetID in Vroom.entityList) {
if (targetID !== entityID) {
var target = Vroom.entityList[targetID];
if (target.physicsEnabled) {
// Check if current entity and target is colliding
if (Vroom.collideEntity(entity, target)) {
switch (entity.collisionType) {
case VroomEntity.DISPLACE:
Vroom.resolveTestTest(entity, target);
break;
}
}
}
}
}
}
}
},
Here is the code for the actual collision detection. This also seems to work alright.
collideEntity: function(entity, target) {
if (entity.getBottom() < target.getTop() || entity.getTop() > target.getBottom() || entity.getRight() < target.getLeft() || entity.getLeft() > target.getRight()) {
return false;
}
return true;
},
Here is where the problems start to pop up. I want the entity to simply be "pushed" out of the target entity and have the velocity set to 0. This works fine as long as both the entity and the target are perfect squares. If let's say the entity (the player figure in the gif) is a rectangle, then the collision will "slipp" when colliding the longest sides (the X axis) with the target (the square). If I swap the player dimensions so that it is short and wide, then the same problem appears for the Y axis instead.
resolveTestTest: function(entity, target) {
var normalizedX = (target.getMidX() - entity.getMidX());
var normalizedY = (target.getMidY() - entity.getMidY());
var absoluteNormalizedX = Math.abs(normalizedX);
var absoluteNormalizedY = Math.abs(normalizedY);
console.log(absoluteNormalizedX, absoluteNormalizedY);
// The collision is comming from the left or right
if (absoluteNormalizedX > absoluteNormalizedY) {
if (normalizedX < 0) {
entity.pos.x = target.getRight();
} else {
entity.pos.x = target.getLeft() - entity.dim.width;
}
// Set velocity to 0
entity.vel.x = 0;
// The collision is comming from the top or bottom
} else {
if (normalizedY < 0) {
entity.pos.y = target.getBottom();
} else {
entity.pos.y = target.getTop() - entity.dim.height;
}
// Set velocity to 0
entity.vel.y = 0;
}
},
Collision on the Y axis works with these shapes
Collision on the X axis slips with these shapes
What can I do to fix this slipping problem? I have been bashing my head against this for the last 5 days, so I would be immensely grateful if some one could help push me in the right direction!
Thank you :)
-- EDIT: --
The slipping also happens if only moving in one direction along the left or right side.
-- EDIT 2 WORKING CODE: --
See my answer below for an example of the working code!
The important logical error you have made is this line:
if (absoluteNormalizedX > absoluteNormalizedY) {
This only works if both entities are square.
Consider a near-extremal case for your X-slipping example: if they almost touch at the corner:
Although the diagram is a little exaggerated, you can see that absoluteNormalizedX < absoluteNormalizedY in this case - your implementation would move on to resolve a vertical collision instead of the expected horizontal one.
Another error is that you always set the corresponding velocity component to zero regardless of which side the collision is on: you must only zero the component if is it in the opposite direction to the collision normal, or you won't be able to move away from the surface.
A good way to overcome this is to also record the collided face(s) when you do collision detection:
collideEntity: function(entity, target) {
// adjust this parameter to your liking
var eps = 1e-3;
// no collision
var coll_X = entity.getRight() > target.getLeft() && entity.getLeft() < target.getRight();
var coll_Y = entity.getBottom() > target.getTop() && entity.getTop() < target.getBottom();
if (!(coll_X && coll_Y)) return 0;
// calculate bias flag in each direction
var bias_X = entity.targetX() < target.getMidX();
var bias_Y = entity.targetY() < target.getMidY();
// calculate penetration depths in each direction
var pen_X = bias_X ? (entity.getRight() - target.getLeft())
: (target.getRight() - entity.getLeft());
var pen_Y = bias_Y ? (entity.getBottom() - target.getUp())
: (target.getBottom() - entity.getUp());
var diff = pen_X - pen_Y;
// X penetration greater
if (diff > eps)
return (1 << (bias_Y ? 0 : 1));
// Y pentration greater
else if (diff < -eps)
return (1 << (bias_X ? 2 : 3));
// both penetrations are approximately equal -> treat as corner collision
else
return (1 << (bias_Y ? 0 : 1)) | (1 << (bias_X ? 2 : 3));
},
updatePhysics: function(step) {
// ...
// pass collision flag to resolver function
var result = Vroom.collideEntity(entity, target);
if (result > 0) {
switch (entity.collisionType) {
case VroomEntity.DISPLACE:
Vroom.resolveTestTest(entity, target, result);
break;
}
}
// ...
}
Using a bit flag instead of a boolean array for efficiency. The resolver function can then be re-written as:
resolveTestTest: function(entity, target, flags) {
if (!!(flags & (1 << 0))) { // collision with upper surface
entity.pos.y = target.getTop() - entity.dim.height;
if (entity.vel.y > 0) // travelling downwards
entity.vel.y = 0;
}
else
if (!!(flags & (1 << 1))) { // collision with lower surface
entity.pos.y = target.getBottom();
if (entity.vel.y < 0) // travelling upwards
entity.vel.y = 0;
}
if (!!(flags & (1 << 2))) { // collision with left surface
entity.pos.x = target.getLeft() - entity.dim.width;
if (entity.vel.x > 0) // travelling rightwards
entity.vel.x = 0;
}
else
if (!!(flags & (1 << 3))) { // collision with right surface
entity.pos.x = target.getRight();
if (entity.vel.x < 0) // travelling leftwards
entity.vel.x = 0;
}
},
Note that unlike your original code, the above also allows corners to collide - i.e. for velocities and positions to be resolved along both axes.
MY WORKING CODE
So with some help and guidance from the amazing #meowgoesthedog I finally got on the right track and found what I was looking for. The problem (as #meowgoesthedog pointed out) was that my code was really only going to work with squares. The solution was to check the intersection of the colliding bodies and solve based on the shortest intersection. Note: this will probably not be a suitable solution if you need accurate physics with small and fast moving objects. The code for finding the intersection depth is based on this: https://github.com/kg/PlatformerStarterKit/blob/0e2fafb8dbc845279fe4116c37b6f2cdd3e636d6/RectangleExtensions.cs which is related to this project: https://msdn.microsoft.com/en-us/library/dd254916(v=xnagamestudio.31).aspx.
Here is my working code:
My physics loop has not been changed much, except for some better names for some functions.
updatePhysics: function(step) {
// Loop through entities and update positions based on velocities
for (var entityID in Vroom.entityList) {
var entity = Vroom.entityList[entityID];
if (entity.physicsEnabled) {
switch (entity.entityType) {
case VroomEntity.KINEMATIC:
entity.pos.x += entity.vel.x * step;
entity.pos.y += entity.vel.y * step;
break;
case VroomEntity.DYNAMIC:
// Dynamic stuff
break;
}
}
}
// Loop through entities and detect collisions. Resolve collisions as they are detected.
for (var entityID in Vroom.entityList) {
var entity = Vroom.entityList[entityID];
if (entity.physicsEnabled && entity.entityType !== VroomEntity.STATIC) {
for (var targetID in Vroom.entityList) {
if (targetID !== entityID) {
var target = Vroom.entityList[targetID];
if (target.physicsEnabled) {
// Check if current entity and target is colliding
if (Vroom.collideEntity(entity, target)) {
switch (entity.collisionType) {
case VroomEntity.DISPLACE:
Vroom.resolveDisplace(entity, target);
break;
}
}
}
}
}
}
}
},
The collision detection remains the same as well.
collideEntity: function(entity, target) {
if (entity.getBottom() < target.getTop() || entity.getTop() > target.getBottom() || entity.getRight() < target.getLeft() || entity.getLeft() > target.getRight()) {
return false;
}
return true;
},
Here is the code that basically fixes the problem. The comments in the code should explain what it does pretty well.
getIntersectionDepth: function(entity, target) {
// Calculate current and minimum-non-intersecting distances between centers.
var distanceX = entity.getMidX() - target.getMidX();
var distanceY = entity.getMidY() - target.getMidY();
var minDistanceX = entity.halfDim.width + target.halfDim.width;
var minDistanceY = entity.halfDim.height + target.halfDim.height;
// If we are not intersecting at all, return 0.
if (Math.abs(distanceX) >= minDistanceX || Math.abs(distanceY) >= minDistanceY) {
return {
x: 0,
y: 0,
};
}
// Calculate and return intersection depths.
var depthX = distanceX > 0 ? minDistanceX - distanceX : -minDistanceX - distanceX;
var depthY = distanceY > 0 ? minDistanceY - distanceY : -minDistanceY - distanceY;
return {
x: depthX,
y: depthY,
};
},
Here is the updated resolving function. It now takes intersection depth in to account when determining axis of collision and then uses the sign of the intersection depth for the colliding axis when determining the direction to resolve.
resolveDisplace: function(entity, target) {
var intersection = Vroom.getIntersectionDepth(entity, target);
if (intersection.x !== 0 && intersection.y !== 0) {
if (Math.abs(intersection.x) < Math.abs(intersection.y)) {
// Collision on the X axis
if (Math.sign(intersection.x) < 0) {
// Collision on entity right
entity.pos.x = target.getLeft() - entity.dim.width;
} else {
// Collision on entity left
entity.pos.x = target.getRight();
}
entity.vel.x = 0;
} else if (Math.abs(intersection.x) > Math.abs(intersection.y)) {
// Collision on the Y axis
if (Math.sign(intersection.y) < 0) {
// Collision on entity bottom
entity.pos.y = target.getTop() - entity.dim.height;
} else {
// Collision on entity top
entity.pos.y = target.getBottom();
}
entity.vel.y = 0;
}
}
},
Thank you all for your help!
The problem may be that you're correcting both X and Y collision based on the same position:
Player is at a certain position. Let's check collision.
Player's bottom right corner overlaps top left corner of object.
X position is corrected: Player is moved to the left.
Player's bottom right corner overlaps top left corner of object.
Y position is corrected: Player is moved up.
End result: The player is moved up and to the left.
You probably need to "get" the player's position again, between checks.
All I need is to have this object travel left and right across the top of the canvas. Currently it spawns and travels right absolutely fine, then stops once it reaches the right edge of the canvas.
//mainEnemy Variables
var mainEnemy_x = 10;
var mainEnemy_y = 10;
var mainEnemyHeight = 50;
var mainEnemyWidth = 25;
var mainEnemyRight = true;
var mainEnemyLeft = false;
var mainEnemy_dx = 2;
//Drawing the Main Enemy
function drawMainEnemy()
{
ctx.beginPath();
ctx.rect(mainEnemy_x, mainEnemy_y, mainEnemyHeight, mainEnemyWidth);
ctx.fillStyle = "green";
ctx.fill();
ctx.closePath();
}
//Movement speed of mainEnemy
if(mainEnemyRight && mainEnemy_x < canvas.width-mainEnemyWidth)
{
mainEnemy_x += 5;
}
else if(mainEnemyLeft && mainEnemy_x > 0)
{
mainEnemy_x -= 5;
}
//mainEnemy moves across the top of the canvas
if(mainEnemy_x + mainEnemy_dx - mainEnemyWidth > canvas.width)
{
mainEnemy_dx = -mainEnemy_dx;
}
ball_x += dx;
ball_y += dy;
mainEnemy_x += mainEnemy_dx;
}
This is all the code relevant to the object I need help with. I've tried just reversing it's x movement, with the mainEnemy_dx = -mainEnemy_dx; line, but this isn't working. I can see this code is an absolute mess at the moment, I just need to get it working then time for some serious cleanup.
Any and all help would be greatly appreciated!
First of all, you have two movement systems. One with the left and right flags and constants added or subtracted from x and the other with dx. You should just use one or the other, the latter being simpler.
For the jitter, you have to either also check that the current dx is positive when going over the right by border (and negative on left) and then switch the sign, or move the object left when a collision with right border is found.
At the moment you are moving the object 7 units right every time, then when border is found only dx is used (2 or -2) but since your object can be over the border it might vibrate between 2 and -2 always. But at least the right branch will always try to move 5 units right even when dx is negative.
Using a debugger to step through the code and inspecting the variables and branches taken while vibrating on the right edge will show exactly how it behaves.
I am writing a simple game (in Javascript) where circular sprites can collide with each other. I store an angle (in degrees) and an x,y for each object. I have the collision detection working, but I need to work out which sprite hit the other. So for two objects colliding which one drove into the other (i.e. the front of which sprite made contact with the 'non front' of the other). Or to put it another way, which one rear ended the other. In the case of very close head on accidents e.g. where they make an absolute direct head on collision (180 degree collision) or are within say 5 degrees of doing so (175-185 degree collision), then I need to spot this and attribute no 'blame' to either sprite. What would the maths, or better still the code, for this be?
var angleA = Math.abs(collidedWith.angle - 180);
var angleB = Math.abs(this.angle - 180);
var angleConsideredHeadOn = 5;
var anglesSubtracted = Math.abs(angleA - angleB);
if (anglesSubtracted < angleConsideredHeadOn) {
var headOn = true;
}
if (anglesSubtracted >= angleConsideredHeadOn) {
// There was a non-head on crash
var xA = collidedWith.velocityX;
var yA = collidedWith.velocityY;
var xB = this.velocityX;
var yB = this.velocityY;
// Need to determine which sprites 'front' collided with the other's side or read
}
To detect the head-on case, take the dot product of their two (pre-impact) velocity vectors which will give you the cosine between their headings. If that value is less than -0.9 Pi then the collision is head on.
Otherwise, the sprite to blame is the one with the highest absolute velocity (since a slow sprite cannot possibly rear-end a fast sprite).
This seems to work...
// Javascript
// Two objects 'this' and 'collidedWith' have collided
// this code determines who head butted the other
// Based on having an angle and an X and Y velocity (xDir and yDir) where volicity could be negative (going left or up) or positive (going right or down)
// 'degrees' is a function which converts radians to degrees
var angleConsideredHeadOn = 15;
var theta_a = degrees(Math.atan2(this.xDir, this.yDir));
var theta_b = degrees(Math.atan2(collidedWith.xDir, collidedWith.yDir));
var a_to_b = degrees(Math.atan2(this.posY - collidedWith.posY, this.posX - collidedWith.posX)); // Normal angle from 'this's perspective
var b_to_a = -a_to_b % 360; // ditto from collidedWith's perspective
var collision_angle_a = Math.abs(theta_a - a_to_b) % 360
var collision_angle_b = Math.abs(theta_b - b_to_a) % 360
// Collision is close to head on
if (Math.abs(collision_angle_a - collision_angle_b) < angleConsideredHeadOn) return;
//
if (collision_angle_a < collision_angle_b) {
// 'collidedWith' head butted the other object
} else {
// 'this' head butted the other object
}
I’m fairly new to web development and I’ve only ever used jQuery to write my scripts. Today however, I’d like to improve my skills and build a little game that could be used on a smartphone as a web app in vanilla JS.
The game’s pretty straightforward:
You hold your phone in portrait mode and control a character that stays at the bottom of the screen and has to dodge objects that are falling on him. The character can only move left or right and thus always stays on the same x-axis. In order to control him, your finger has to stay on the screen. Once you take it off, you lose. Also, the move isn’t triggered by tapping the screen, but by moving your finger left or right.
For now, I’ve only been experimenting to get the hang of touchevents and was able to make the character move when swiping:
document.addEventListener('touchmove',function(e){
e.preventDefault(); //disable scroll
var board = document.getElementById(‘board);
var character = document.getElementById(‘character’);
if (e.targetTouches.length === 1) {
var touch = e.targetTouches[0];
board.classList.add(‘moving’);
character.style.left = touch.pageX + 'px';
}
}, false);
(The ‘moving’ class is used to move the background-position of the board and animate the character’s sprite in plain CSS.)
Separately, I made a little script that puts objects with random classes in a container with a set interval. These objects are then animated in css and fall from the top to the bottom of the screen.
Now, here comes the tricky part: the collision detection.
As I said, I’m new to development and vanilla JS, so I searched a bit to figure out how to detect when two objects collide, and it seems that most tutorials do this using canvases. The thing is, I’ve never used them and they scare me quite a bit. What’s more, I think it would render what I’ve done so far useless.
I’m okay with trying the canvas way, but before I do, I’d like to know if there’s any other way to detect if two moving objects collide?
Also, if there turns out to be no real way to do this without canvas, I plan on using this tutorial to learn how to build the app. However, this game wasn’t built for touchscreen devices, and the spaceship’s position changes on certain keystrokes (left & right) :
function update() {
if (keydown.left) {
player.x -= 5;
}
if (keydown.right) {
player.x += 5;
}
player.x = player.x.clamp(0, CANVAS_WIDTH - player.width);
}
My question is: how should I do to update the position using touchmove instead of keystrokes?
Thank you all in advance.
1) the idea : 'if you stop touching, you loose', is just a bad idea, drop it.
2) most convenient way to control is to handle any touch event (touch start/move/end/cancel), and to have the character align on the x coordinate of this event.
3) the intersection test is just a basic boundig box intersection check.
I made a very basic demo here, that uses touch, but also mouse to ease testing :
http://jsbin.com/depo/1/edit?js,output
a lot of optimisations are possible here, but you will see that touches adjust the ship's position, and that collisions are detected, so it will hopefully lead you to your own solution
Edit : i added default to 0 for left, top, in case they were not set.
boilerplate code :
var collisionDisplay = document.getElementById('collisionDisplay');
// hero ship
var ship = document.getElementById('ship');
ship.onload = launchWhenReady ;
// bad ship
var shipBad = document.getElementById('shipBad');
shipBad.onload = launchWhenReady ;
// image loader
imagesCount = 2 ;
function launchWhenReady() {
imagesCount --;
if (imagesCount) return;
setInterval(animate, 20);
}
var shipBadY = 0;
touch events :
// listen any touch event
document.addEventListener('touchstart', handleTouchEvent, true);
document.addEventListener('touchmove', handleTouchEvent, true);
document.addEventListener('touchend', handleTouchEvent, true);
document.addEventListener('touchcancel', handleTouchEvent, true);
// will adjust ship's x to latest touch
function handleTouchEvent(e) {
if (e.touches.length === 0 ) return;
e.preventDefault();
e.stopPropagation();
var touch = e.touches[0];
ship.style.left = (touch.pageX - ship.width / 2) + 'px';
}
animation :
// animation loop
function animate() {
// move ship
shipBadY += 1;
shipBad.style.top = Math.ceil(shipBadY) + 'px';
// test collision
var isColliding = testCollide(shipBad);
collisionDisplay.style.display = isColliding ? 'block' : 'none';
}
collision :
// collision test when the enemy and the ship are images
function testCollide(enemi) {
var shipPosX = parseInt(ship.style.left) || 0 ;
var shipPosY = parseInt(ship.style.top) || 0 ;
var shipWidth = ship.width ;
var shipHeight = ship.height;
var badX = parseInt(enemi.style.left) || 0 ;
var badY = parseInt(enemi.style.top) || 0 ;
var badWidth = enemi.width;
var badHeight = enemi.height;
return bBoxIntersect(shipPosX, shipPosY, shipWidth, shipHeight,
badX, badY, badWidth, badHeight);
}
EDIT : in case you're not using images :
// collision test when the enemy and the ship are ** NOT ** images
function testCollide(o) {
var characterPosX = parseInt(character.style.left);
var characterPosY = parseInt(character.style.top);
var characterWidth = parseInt(character.style.width);
var characterHeight = parseInt(character.style.height);
var obstacleX = parseInt(o.style.left) || 0 ;
var obstacleY = parseInt(o.style.top) || 0 ;
var obstacleWidth = parseInt(o.style.width);
var obstacleHeight = parseInt(o.style.height);
return boundingBoxIntersect(characterPosX, characterPosY, characterWidth, characterHeight, obstacleX, obstacleY, obstacleWidth, obstacleHeight);
}
function bBoxIntersect(x1, y1, w1, h1, x2, y2, w2, h2) {
return !(x1 + w1 < x2 || x1 > x2 + w2 || y1 + h1 < y2 || y1 > y2 + w2);
}
mouse events :
// -----------------------------------------------------
// Handle mouse event for easy testing on Browser
document.addEventListener('mousemove', handleMouseEvent);
function handleMouseEvent(e) {
ship.style.left = (e.pageX - ship.width / 2) + 'px';
}