Develop Reference

trying to make a drawn line move like a laser in javascript

I made this red line in JavaScript that goes to closest target (balloon 1 to 3) to the player but I need to make it so that it moves like a laser starting from player position into the target position. I thought about multiple ways of implementing this with no luck.
function Tick() {
// Erase the sprite from its current location.
eraseSprite();
for (var i = 0; i < lasers.length; i++) {
lasers[i].x += lasers[i].direction.x * laserSpeed;
lasers[i].y += lasers[i].direction.y * laserSpeed;
//Hit detection here
}
function detectCharClosest() {
var ballon1char = {
x: balloon1X,
y: balloon1Y
};
var ballon2char = {
x: balloon2X,
y: balloon2Y
};
var ballon3char = {
x: balloon3X,
y: balloon3Y,
};
ballon1char.distanceFromPlayer = Math.sqrt((CharX - balloon1X) ** 2 + (CharY - balloon1Y) ** 2);
ballon2char.distanceFromPlayer = Math.sqrt((CharX - balloon2X) ** 2 + (CharY - balloon2Y) ** 2);
ballon3char.distanceFromPlayer = Math.sqrt((CharX - balloon3X) ** 2 + (CharY - balloon3Y) ** 2);
var minDistance = Math.min(
ballon1char.distanceFromPlayer,
ballon2char.distanceFromPlayer,
ballon3char.distanceFromPlayer);
console.log(ballon1char);
console.log(ballon2char);
console.log(ballon3char);
for (let i = 0; i < 3; i++) {
if (minDistance == ballon1char.distanceFromPlayer)
return ballon1char
if (minDistance == ballon2char.distanceFromPlayer)
return ballon2char
if (minDistance == ballon3char.distanceFromPlayer)
return ballon3char
}
}
function loadComplete() {
console.log("Load is complete.");
canvas = document.getElementById("theCanvas");
ctx = canvas.getContext("2d");
myInterval = self.setInterval(function () { Tick() }, INTERVAL);
myInterval = self.setInterval(function () { laserTicker(detectCharClosest()) }, 2000);
function laserTicker(balloon) {
//gets the closest ballon to go to
laserDo(balloon);
}
function laserDo(balloon) {
ctx.beginPath();
ctx.lineWidth = 2;
ctx.strokeStyle = "#F44336"; // "red";
ctx.moveTo(CharX + 16, CharY + 16);
ctx.lineTo(balloon.x, balloon.y);
// lasers.push({x: })
ctx.stroke();
}
I didn't put all of my code here so If something doesn't make sense please tell me. I'm still new to JavaScript and learning it. One way I thought I could make this work was by taking the distance between the player and the target and dividing it by the speed on the x and y axis then changing having it start from the player position and keeps on adding up on both axis until it reaches the target. That didn't work out though. If you have any suggestions then please tell me.
Thanks

Controlling state

getMouseXY = function(e) {
tempX = e.pageX
tempY = e.pageY
if (tempX < 0){tempX = 0}
if (tempY < 0){tempY = 0}
document.getElementById("circle1").style.top = (tempY - 25) + "px";
document.getElementById("circle1").style.left = (tempX - 25) + "px";
return true
}
document.onmousemove = getMouseXY;
trackCircle = function() {
document.getElementById("circle1").style.top = "10px";
document.getElementById("circle1").style.left = "10px";
}
document.getElementById("circle1").addEventListener("click", trackCircle);
<div id="circle1" style="width:50px;height:50px;background-color:orange;border-radius:50px;position:absolute;"></div>
The idea is the circle tracks your mouse wherever it goes, until you click, then it goes back to its resting spot. The problem is, when I move the mouse again it undoes the resting position, and returns to tracking the document.onmousemove The plan is for it to only resume tracking, once in rest, after you re-hover "circle1" ... and then resumes tracking with document.onmousemove
I know I could call something like this instead of document.onmousemove:
document.getElementById("circle1").addEventListener('mousemove', getMouseXY);
But the "is the mouse hovering over this specific element?" event is to imprecise and you end up losing your tracking a lot when you move the mouse around quickly.
Seems like I need to build some kind of state machine where its either trackingON or trackingOFF. Where trackingOFF is triggered by clicking the circle and trackingON is triggered by hovering the circle (but then the actual tracking uses document.onmousemove

You need a flag to specify that "I have clicked, stop tracking my mouse" to be set when you click and a check to say "I have moved my mouse over the circle, resume tracking me"
Here is the updated fiddle: http://jsfiddle.net/ub9v9p0j/8/
and the actual code:
var stopTracking = false;
getMouseXY = function(e) {
tempX = e.pageX
tempY = e.pageY
var circle = document.querySelector('#circle1');
var r = circle.offsetWidth / 2;
if (tempX < 0){tempX = 0}
if (tempY < 0){tempY = 0}
if (stopTracking) {
if (Math.pow(tempX - circle.offsetLeft - r, 2) + Math.pow(tempY - circle.offsetTop - r, 2) < r * r) {
stopTracking = false;
} else {
return;
}
}
document.getElementById("circle1").style.top = (tempY - 25) + "px";
document.getElementById("circle1").style.left = (tempX - 25) + "px";
return true
}
document.onmousemove = getMouseXY;
trackCircle = function() {
document.getElementById("circle1").style.top = "10px";
document.getElementById("circle1").style.left = "10px";
stopTracking = true;
}
document.getElementById("circle1").addEventListener("click", trackCircle);

Mouse position is only read on the first frame

i have been having trouble with reading a mouse position on a canvas. The code is working (semi) correctly as it reads the position when clicking he canvas in IE but only on one frame, in chrome it is just displaying the value as 0.
Here is the full code:
<script>
var blip = new Audio("blip.mp3");
blip.load();
var levelUp = new Audio("levelUp.mp3");
levelUp.load();
var canvas = document.getElementById('game');
var context = canvas.getContext('2d');
context.font = '18pt Calibri';
context.fillStyle = 'white';
//load and draw background image
var bgReady = false;
var background = new Image();
background.src = 'images/background.jpg';
background.onload = function(){
bgReady = true;
}
var startMessage = 'Click the canvas to start';
//load plane image
var planeReady = false;
var planeImage = new Image();
planeImage.src = 'images/plane.png';
planeImage.onload = function() {
planeReady = true;
}
//load missile image
var missileReady = false;
var missileImage = new Image();
missileImage.src = 'images/missile-flipped.gif';
missileImage.onload = function() {
missileReady = true;
}
//initialise lives and score
var score = 0;
var lives = 3;
var missilesLaunched = 0;
var missileSpeed = 5;
var level = 1;
var missileX = 960;
var missileY = Math.random() * 500;
if (missileY > 480) {
missileY = 480;
}
function getMousePos(canvas, event) {
return {
x: input.x - rect.left,
y: input.y - rect.top
};
}
function update_images(event) {
var pos = getMousePos(canvas.getBoundingClientRect(), mouseInput);
planeImage.y = pos.y;
missileX = missileX - missileSpeed;
if (missileX < - 70) {
missilesLaunched++;
missileX = 960;
missileY = Math.random() * 500;
if (missileY > 480) {
missileY = 480;
}
blip.play();
score = missilesLaunched;
if (score % 5 == 0) {
missileSpeed = missileSpeed + 2;
level++;
levelUp.play();
}
}
}
function reload_images() {
if (bgReady = true) {
context.drawImage(background, 0, 0);
}
if (planeReady = true) {
context.drawImage(planeImage, 10, planeImage.y);
}
if (missileReady = true) {
context.drawImage(missileImage, missileX, missileY);
}
context.fillText('Lives: ' + lives, 200, 30);
context.fillText('Score: ' + score, 650, 30);
context.fillText('Level: ' + missileSpeed, 420, 30);
context.fillText('Position: ' + missileImage.y, 420, 70);
}
function main(event) {
var mouseInput = { x: 0, y: 0 };
document.addEventListener("mousemove", function (event) {
mouseInput.x = event.clientX;
mouseInput.y = event.clientY;
});
update_images(event);
reload_images();
if (lives > 0) {
window.requestAnimationFrame(main);
}
else {
}
}
function start() {
context.drawImage(background, 0, 0);
context.fillText('Click the canvas to start', 350, 250);
function startMain(event) {
game.removeEventListener("click", startMain);
main(event);
}
canvas.addEventListener("mousedown", startMain);
}
start();
</script>

Joe, you should actually be capturing the mouse position every time you click...
...but you're actually also starting a new game (without stopping the old one), every time you click, too.
First problem: starting game engine several times to draw on the same instance of the canvas
Solution:
In your start function, you need to remove the mousedown event listener, after you've triggered it.
function start () {
// ... other setup
function startMain (event) {
canvas.removeEventListener("click", startMain);
main(event);
}
canvas.addEventListener("click", startMain);
}
Now it will only listen for the first click, before starting, and will only start once.
Second Problem: mouse doesn't update as expected
Solution: two issues here...
...first, you are passing event into main on first call...
...after that, you're passing main into requestAnimationFrame.
requestAnimationFrame won't call it with an event, it will call it with the number of microseconds (or ms or some other unit as a fractional precision of ms) since the page was loaded.
So the first time you got main({ type: "mousedown", ... });.
The next time you get main(4378.002358007);
So lets refactor the startMain we had above, so that main never ever collects an event, just a time.
function startMain ( ) {
canvas.removeEventListener("click", startMain);
requestAnimationFrame(main);
}
The next problem is that even if you were getting just events, you're only ever capturing a click event (which as we mentioned earlier, fires a new copy of the game logic).
Your solution is to separate the code which catches mouse events from the code which reads mouse position.
var mouseInput = { x: 0, y: 0 };
document.addEventListener("mousemove", function (event) {
mouseInput.x = event.clientX;
mouseInput.y = event.clientY;
});
function getMousePos (rect, input) {
return {
x : input.x - rect.left,
y : input.y - rect.top
};
}
// currently in updateImages (should not be there, but... a different story)
var pos = getMousePos(canvas.getBoundingClientRect(), mouseInput);
You've got other problems, too...
You're calling getMousePos and passing in game at the moment. I don't see where game is defined in your JS, so either you're making game somewhere else (begging for bugs), or it's undefined, and your app blows up right there.
You should really be building this with your console / dev-tools open, in a hands-on fashion, and cleaning bugs in each section, as you go.

Raphael transform object diagonally and infinite setIntervals

I'm working on a small animation where the user drags a circle and the circle returns back to the starting point. I figured out a way to have the circle return to the starting point. The only problem is that it will hit one of the sides of the frame before returning. Is it possible for it to go straight back (follow the path of a line drawn between the shape and starting point).
The other problem is that my setInterval doesn't want to stop. If you try pulling it a second time it would pull it back before you release your mouse. It also seems to speed up after every time. I have tried using a while loop with a timer but the results weren't as good. Is this fixable?
var paper = Raphael(0, 0, 320, 200);
//var path = paper.path("M10 10L40 40").attr({stoke:'#000000'});
//var pathArray = path.attr("path");
var circle = paper.circle(50, 50, 20);
var newX;
var newY;
circle.attr("fill", "#f00");
circle.attr("stroke", "#fff");
var start = function () {
this.attr({cx: 50, cy: 50});
this.cx = this.attr("cx"),
this.cy = this.attr("cy");
},
move = function (dx, dy) {
var X = this.cx + dx,
Y = this.cy + dy;
this.attr({cx: X, cy: Y});
},
up = function () {
setInterval(function () {
if(circle.attr('cx') > 50){
circle.attr({cx : (circle.attr('cx') - 1)});
} else if (circle.attr('cx') < 50){
circle.attr({cx : (circle.attr('cx') + 1)});
}
if(circle.attr('cy') > 50){
circle.attr({cy : (circle.attr('cy') - 1)});
} else if (circle.attr('cy') < 50){
circle.attr({cy : (circle.attr('cy') + 1)});
}
path.attr({path: pathArray});
},2);
};
circle.drag(move, start, up);
Here's the Jfiddle: http://jsfiddle.net/Uznp2/
Thanks alot :D

I modified the "up" function to the one below
up = function () {
//starting x, y of circle to go back to
var interval = 1000;
var startingPointX = 50;
var startingPointY = 50;
var centerX = this.getBBox().x + (this.attr("r")/2);
var centerY = this.getBBox().y + (this.attr("r")/2);
var transX = (centerX - startingPointX) * -1;
var transY = (centerY - startingPointY) * -1;
this.animate({transform: "...T"+transX+", "+transY}, interval);
};
and the "start" function as follows:
var start = function () {
this.cx = this.attr("cx"),
this.cy = this.attr("cy");
}
Is this the behavior you are looking for? Sorry if I misunderstood the question.

If the circle need to get back to its initial position post drag, we can achieve that via simple animation using transform attribute.
// Assuming that (50,50) is the location the circle prior to drag-move (as seen in the code provided)
// The animation is set to execute in 1000 milliseconds, using the easing function of 'easeIn'.
up = function () {
circle.animate({transform: 'T50,50'}, 1000, 'easeIn');
};
Hope this helps.

Collisions in simple javascript game

I'm writing a simple game in javascript and I'm wondering what the best way to handle collisions between the player and the world objects.
<script>
var isJumping = false;
var isFalling = false;
var w = 1;
var recwidth = 400;
var recheight = 400;
var xpos = 50;
var ypos = 279;
window.onload = function() {
var FPS = 30;
var ground = new myObject();
setInterval(function() {
clear();
draw();
ground.draw(0, 325);
ground.draw(125,325)
}, 1000/FPS);
};
function myObject(){
this.draw = function drawground(groundx, groundy){
var canvas = document.getElementById('canvas')
var context = canvas.getContext('2d');
//context.fillRect(xpos,ypos,100,100);
var img=new Image()
img.src="ground.png"
img.onload = function() {
context.drawImage(img,groundx,groundy)}
}
};
function jump()
{
var t=.1;
isJumping=true;
var jumpint= setInterval(function() {
yup = 12*t-(5*t*t);
ypos= ypos - yup;
t = t + .1
if(yup < 0)
{
isJumping = false;
isFalling = true;
clearInterval(jumpint);
jumpint = 0;
fall();
return;
}
}, 20);
}
function fall()
{
t=.10
var fallint= setInterval(function() {
ydown = (5*t*t);
ypos= ypos + ydown;
t = t + .1
if(ypos > 275)
{
isFalling == false;
clearInterval(fallint);
fallint = 0;
return;
}
}, 20);
}
function changex(x){
xpos = xpos + (x);
//clear();
//draw();
}
function changey(y){
ypos = ypos + (y);
//clear();
//draw();
}
function draw(){
var canvas = document.getElementById('canvas')
var context = canvas.getContext('2d');
var img=new Image()
img.src="character.png"
img.onload = function() {
context.drawImage(img,xpos,ypos)}
}
function clear(){
var canvas = document.getElementById('canvas')
var context = canvas.getContext('2d');
context.clearRect(0,0, canvas.width, canvas.height);
}
document.onkeydown = function(event) {
var keyCode;
if(event == null)
{
keyCode = window.event.keyCode;
}
else
{
keyCode = event.keyCode;
}
switch(keyCode)
{
// left
case 37:
//left
changex(-5);
break;
// up
case 38:
// action when pressing up key
jump();
break;
// right
case 39:
// action when pressing right key
changex(5);
break;
// down
case 40:
// action when pressing down key
changey(5);
break;
default:
break;
}
}
</script>
So, as you can see I'm creating two objects so far, and the player stops falling at any arbitrary point. I feel collisions at this stage wont be too difficult, but once I start adding more I feel it's going to get more difficult. I'm not going to be using the instance of the object with the same image for each instance of the object, so at some point I'm going to change the myobject function to be able to accept the image as a parameter, and then checking for collisions will be a bit more tricky. I also plan on making this into a side scroller, so once one end the map is hit it changes into the next area, which is going to cause performance issues. If I'm checking for collisions on every single object in the entire game every interval I imagine things are going to get slow. What is going to be the best way to limit the number of collisions checked? Obviously, if the object isn't on screen there is no need to check it, but is there a way to limit that. I'm thinking of making an array for every frame of the game, and filling that array with it's objects. Then, only check the array the of the frame the player is currently in. Is this feasible or still going to cause too many issues? Any help is greatly appreciated.

If you want pixel perfect collisions, I have some plain javascript code that worked for me with canvas2d rendering context.
function collide(sprite, sprite2, minOpacity=1) {
// Rectangular bounding box collision
if (sprite.x < sprite2.x + sprite2.width && sprite.x + sprite.width > sprite2.x && sprite.y < sprite2.y + sprite2.height && sprite.y + sprite.height > sprite2.y) {
// Finds the x and width of the overlapping area
var overlapX = (this.rect.x > other.rect.x) ? [this.rect.x, (other.rect.x + other.rect.width) - this.rect.x + 1] : [other.rect.x, (this.rect.x + this.rect.width) - other.rect.x + 1];
// Finds the y and height of the overlapping area
var overlapY = (this.rect.y + this.rect.height > other.rect.y + other.rect.height) ? [this.rect.y, (other.rect.y + other.rect.height) - this.rect.y + 1] : [other.rect.y, (this.rect.y + this.rect.height) - other.rect.y + 1];
// Creates a canvas to draw sprite.image to
var spriteImageCanvas = new OffscreenCanvas(overlapX[0] + overlapX[1], overlapY[0] + overlapY[1]);
var spriteImageCanvasContext = spriteImageCanvas.getContext("2d");
// Draws sprite.image to spriteImageCanvasContext
spriteImageCanvasContext.drawImage(this.image, sprite.x, sprite.y, sprite.width, sprite.height);
// Creates a canvas to draw sprite2.image to
var sprite2ImageCanvas = new OffscreenCanvas(overlapX[0] + overlapX[1], overlapY[0] + overlapY[1]);
var sprite2ImageCanvasContext = otherImageCanvas.getContext("2d");
// Draws sprite2.image to sprite2ImageCanvasContext
sprite2ImageCanvasContext.drawImage(sprite2.image, sprite2.x, sprite2.y, sprite2.width, sprite2.height);
// Loops through the x coordinates in the overlapping area
for (var x = overlapX[0]; x <= overlapX[0] + overlapX[1]; x++) {
// Loops through the y coordinates in the overlapping area
for (var y = overlapY[0]; y <= overlapY[0] + overlapY[1]; y++) {
if (/* Checks if the pixel at [x, y] in the sprite image has an opacity over minOpacity input */ thisImageCanvasContext.getImageData(x, y, 1, 1).data[3] >= minOpacity && /* Checks if the pixel at [x, y] in the sprite2 image has an opacity over minOpacity input */ otherImageCanvasContext.getImageData(x, y, 1, 1).data[3] >= minOpacity) {
return true;
};
};
};
};
}
Or if you just want rectangular collision, use the first if statement in the function.