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

How to start function at specific scroll position on page?

I'm experimenting with the following code where images flip through in a canvas.
If I put the canvas, let's say at the middle of my page, I was wondering if there's a way to only make the images flip through once the viewer gets to that specific section of the page.
Right now, from the looks of it, the images start flipping through right at the top of the page, immediately when you scroll down. By the time you get to the middle of the page where the actual canvas is, the images have already finished flipping through, and it's stopped on the last frame.
I assume I have to set the function to only trigger after the user scrolls to a specific number of pixels on the Y-axis? What's the best way to do so?
Please see code below.
Thanks!
var images = new Array();
var currentLocation = 0;
var totalImages = 200;
for (var i = 1; i < totalImages; i++) {
var img = new Image;
var slug = '000' + i;
img.src = 'https://s3.amazonaws.com/clearmotion/hero/high-min/frame' + slug.slice(-3) + '-low.jpg'
images.push(img);
}
var c = document.getElementById("background");
var ctx = c.getContext("2d");
var mouseWheel = function() {
var newLocation = null;
window.addEventListener('wheel', function(e) {
e.preventDefault(); // No scroll
// update our variable at high frequency
var delta = Math.max(-1, Math.min(1, e.deltaY));
if (delta == -1) currentLocation += 1;
if (delta == 1) currentLocation -= 1;
if (currentLocation < 0) currentLocation = 0;
if (currentLocation >= (totalImages - 1)) currentLocation = (totalImages - 1);
if (newLocation === null) { // if set, we already are waiting to draw
requestAnimationFrame(setImage);
}
newLocation = currentLocation;
});
function setImage() {
if (images[newLocation]) {
ctx.fillRect(0, 0, c.width, c.height);
ctx.drawImage(images[newLocation], 0, 0, 1000, 1000);
}
newLocation = null; // so the throttler knows we can draw again
}
}
images[0].onload = function() {
ctx.fillRect(0, 0, c.width, c.height);
ctx.drawImage(images[currentLocation], 0, 0, 1000, 1000);
mouseWheel();
};
<canvas id="background" width="1000" height="1000"></canvas>

You can actually start make the images flip through once the viewer gets to that specific section of the page by using The Intersection Observer API
So you have to detect when your element in the the viewport, the canvas in this case.
To do this you have multiple ways.
By using Observer API
const element = document.querySelector("#background")
const Ob = new IntersectionObserver((entries) => {
if (entries[0].intersectionRatio <= 0) {
// Not in the viewport
} else {
// In the viewport
// You're code here
}
});
Ob.observe(element);
Or if you want to do it in you're own.
You can use this and adapt it if needed
function elementInViewport(el) {
var top = el.offsetTop
var height = el.offsetHeight;
while(el.offsetParent) {
el = el.offsetParent;
top += el.offsetTop;
}
return (
top >= window.pageYOffset &&
(top + height) <= (window.pageYOffset + window.innerHeight)
);
}

different pages in a canvas game

The Problem
I am creating a game using the HTML5 Canvas, the game has a main menu, the main menu has multiple buttons for you to choose. I am finding it difficult and confusing how I would, for example if the user presses the 'Play' button, to show the game. Here is an image of the main menu:
The Question
The question is how would I get from this page to another in my game?
I think you get the idea. I deliberately created the menu using the canvas, I know I could of made the menu using HTML for example but I cant as this is an example for students of what Canvas can do, whats good and bad etc.
The Code
<html>
<head>
<title>Sean Coyne</title>
</head>
<body onload="start_game()">
<body>
<div style id="canvas">
<canvas id="myCanvas" style="border:5px solid #410b11" height="320" width="480">
<p>Your browser does not support HTML5!</p>
</canvas>
<script type="text/javascript">
//Referencing the canvas
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var width = canvas.getAttribute('width');
var height = canvas.getAttribute('height');
//Finding the position of the mouse
var mouseX;
var mouseY;
//Images
var bgImage = new Image();
var logoImage = new Image();
var playImage = new Image();
var instructImage = new Image();
var settingsImage = new Image();
var aboutImage = new Image();
var peaceImage = new Image();
var backgroundY = 0;
var speed = 1;
//Arrays below used for mouse over function
var buttonX = [130,110,130,160];
var buttonY = [100,140,180,220];
var buttonWidth = [96,260,182,160];
var buttonHeight = [40,40,40,40];
var peaceX = [0,0];
var peaceY = [0,0];
var peaceWidth = 35;
var peaceHeight = 35;
var peaceVisible = false;
var peaceSize = peaceWidth;
var peaceRotate = 0;
var frames = 30;
var timerId = 0;
var fadeId = 0;
var time = 0.0;
peaceImage.src = "Images/peace.png";
bgImage.onload = function(){
context.drawImage(bgImage, 0, backgroundY);
};
bgImage.src = "Images/background.png";
logoImage.onload = function(){
context.drawImage(logoImage, 50, -10);
}
logoImage.src = "Images/logo.png";
playImage.onload = function(){
context.drawImage(playImage, buttonX[0], buttonY[0]);
}
playImage.src = "Images/play.png";
instructImage.onload = function(){
context.drawImage(instructImage, buttonX[1], buttonY[1]);
}
instructImage.src = "Images/instructions.png";
settingsImage.onload = function(){
context.drawImage(settingsImage, buttonX[2], buttonY[2]);
}
settingsImage.src = "Images/settings.png";
aboutImage.onload = function(){
context.drawImage(aboutImage, buttonX[3], buttonY[3]);
}
aboutImage.src = "Images/about.png";
timerId = setInterval("update()", 1000/frames);
canvas.addEventListener("mousemove", checkPos);
canvas.addEventListener("mouseup", checkClick);
function update() {
clear();
move();
draw();
}
function clear() {
context.clearRect(0, 0, width, height);
}
function move(){
backgroundY -= speed;
if(backgroundY == -1 * height){
backgroundY = 0;
}
if(peaceSize == peaceWidth){
peaceRotate = -1;
}
if(peaceSize == 0){
peaceRotate = 1;
}
peaceSize += peaceRotate;
}
function draw(){
context.drawImage(bgImage, 0, backgroundY);
context.drawImage(logoImage, 50,-10);
context.drawImage(playImage, buttonX[1], buttonY[0]);
context.drawImage(instructImage, buttonX[2], buttonY[1]);
context.drawImage(settingsImage, buttonX[2], buttonY[2]);
context.drawImage(aboutImage, buttonX[3], buttonY[3]);
if(peaceVisible == true){
context.drawImage(peaceImage, peaceX[0] - (peaceSize/2), peaceY[0], peaceSize, peaceHeight);
context.drawImage(peaceImage, peaceX[2] - (peaceSize/2), peaceY[2], peaceSize, peaceHeight);
}
}
function checkPos(mouseEvent){
if(mouseEvent.pageX || mouseEvent.pageY == 0){
mouseX = mouseEvent.pageX - this.offsetLeft;
mouseY = mouseEvent.pageY - this.offsetTop;
}else if(mouseEvent.offsetX || mouseEvent.offsetY == 0){
mouseX = mouseEvent.offsetX;
mouseY = mouseEvent.offsetY;
}
for(i = 0; i < buttonX.length; i++){
if(mouseX > buttonX[i] && mouseX < buttonX[i] + buttonWidth[i]){
if(mouseY > buttonY[i] && mouseY < buttonY[i] + buttonHeight[i]){
peaceVisible = true;
peaceX[0] = buttonX[i] - (peaceWidth/2) - 2;
peaceY[0] = buttonY[i] + 2;
peaceX[1] = buttonX[i] + buttonWidth[i] + (peaceWidth/2);
peaceY[1] = buttonY[i] + 2;
}
}else{
peaceVisible = false;
}
}
}
function checkClick(mouseEvent){
for(i = 0; i < buttonX.length; i++){
if(mouseX > buttonX[i] && mouseX < buttonX[i] + buttonWidth[i]){
if(mouseY > buttonY[i] && mouseY < buttonY[i] + buttonHeight[i]){
fadeId = setInterval("fadeOut()", 1000/frames);
clearInterval(timerId);
canvas.removeEventListener("mousemove", checkPos);
canvas.removeEventListener("mouseup", checkClick);
}
}
}
}
function fadeOut(){
context.fillStyle = "rgba(0,0,0, 0.2)";
context.fillRect (0, 0, width, height);
time += 0.1;
if(time >= 2){
clearInterval(fadeId);
time = 0;
timerId = setInterval("update()", 1000/frames);
canvas.addEventListener("mousemove", checkPos);
canvas.addEventListener("mouseup", checkClick);
}
}
</script>
</body>
</html>

What I usually do is have a switch statement inside the draw loop, and a state variable which holds the current game state (menu, playing, etc...).
Then, based on the current game state you only draw the objects required for the current scene.
Something like this:
var STATES = {
Menu: 0,
PauseMenu: 1,
Playing: 2
};
var currentState = STATES.Menu;
...
function draw() {
switch(currentState) {
case STATES.Menu:
// Draw buttons, etc..
break;
case STATES.Playing:
// Draw the game screen, the player, etc...
break;
}
}
When the user presses the Play button the only thing you have to do is:
function onPlayButtonClick() {
currentState = STATES.Playing;
// Starting the next frame the new state will be "magically" drawn
}
If you don't like the switch statement, you can create a State class that has a draw method. Then you can simply create new states, each with it's own drawing method and in the main draw loop only call the draw method of the current state.
Same goes for the update function, each state has it's own update function (in the main menu you update buttons or animate things, while playing the game you update the game world and run your physics). So, based on the current state your update function is actually different. It's up to you how you structure your code and how you call different functions based on the current state.

In each text option, you should create a smaller Canvas, only with the option text and add a 'click' event with the callbacks.
Tip: You don't need another page, just erase the main canvas and draw what you want.

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.

Free memory on FPS system

I start on KineticJS (and on Canvas) and i'm creating a small game for learn...
Right now, I have just 2 layers :
First with a map composed by Kinetic.Image
Second with the last time who game as draw.
I want refresh display X time per second but after 20 or 30 times the game are really slow.. And it's the same when I flood event click ( who launch the draw function too)...
Moreover, i can see in the second layer : the old text are never clean, the new are added on top... :/
var stage;
var layers = {};
var CANEVAS_WIDTH = 800;
var CANEVAS_HEIGHT = 600;
var MAP_WIDTH = 10;
var MAP_HEIGHT = 10;
var MAPPING_WIDTH = 150;
var MAPPING_HEIGHT = 88;
var LEFT_X = 0;
var LEFT_Y = MAP_WIDTH*MAPPING_HEIGHT/2;
var TOP_X = MAP_WIDTH/2*MAPPING_WIDTH;
var TOP_Y = 0;
var VIEW_X = 0;
var VIEW_Y = 0;
var CURSOR_X = 6;
var CURSOR_Y = 0;
var images = {};
function loadImages(sources, callback)
{
var loadedImages = 0;
var numImages = 0;
// get num of sources
for (var src in sources)
numImages++;
for (var src in sources)
{
images[src] = new Image();
images[src].onload = function(){
if (++loadedImages >= numImages)
callback();
};
images[src].src = sources[src];
}
}
function getMouseInfo(mousePos)
{
var info = {screen_x : mousePos.x,
screen_y : mousePos.y,
mouse_x : mousePos.x+VIEW_X,
mouse_y : mousePos.y+VIEW_Y-LEFT_Y,
onMap : 0,
map_x : -1,
map_y : -1};
map_x = -(info.mouse_y - ((LEFT_Y * info.mouse_x) / TOP_X)) / MAPPING_HEIGHT;
map_y = -(-info.mouse_y - ((LEFT_Y * info.mouse_x) / TOP_X)) / MAPPING_HEIGHT;
if(map_x >= 0 && map_x < MAP_WIDTH && map_y >= 0 && map_y < MAP_HEIGHT)
{
info.map_y = parseInt(map_y);
info.map_x = parseInt(map_x);
info.onMap = 1;
}
return info;
}
function draw()
{
drawMap();
drawFPS();
stage.add(layers.mapLayer);
stage.add(layers.fpsLayer);
}
function drawFPS()
{
layers.fpsLayer.clear();
var fps = new Kinetic.Shape(function(){
var date = new Date();
var time = date.getTime();
var context = this.getContext();
context.beginPath();
context.font = "12pt Calibri";
context.fillStyle = "red";
context.fillText("FPS : "+time, 10, 20);
});
layers.fpsLayer.add(fps);
}
function drawMap()
{
var x=0,y=0;
layers.mapLayer.clear();
var s = new Kinetic.Shape(function(){
var context = this.getContext();
context.beginPath();
context.rect(0, 0, CANEVAS_WIDTH, CANEVAS_HEIGHT);
context.fillStyle = "#000";
context.fill();
context.closePath();
});
layers.mapLayer.add(s);
for(x=0; x<MAP_WIDTH; x++)
for(y=0;y<MAP_HEIGHT; y++)
{
var img = new Kinetic.Image({
image: ((x==CURSOR_X && y==CURSOR_Y)?images.testMapCursor:images.testMap)
});
img.x = x*MAPPING_WIDTH/2 + y*MAPPING_WIDTH/2 - VIEW_X;
img.y = (MAP_WIDTH-1)*MAPPING_HEIGHT/2 - x*MAPPING_HEIGHT/2 + y*MAPPING_HEIGHT/2 - VIEW_Y;
layers.mapLayer.add(img);
}
}
function changeCursorPosition(cursor_x, cursor_y)
{
CURSOR_X = cursor_x;
CURSOR_Y = cursor_y;
draw();
}
function initStage()
{
layers.mapLayer = new Kinetic.Layer();
layers.fpsLayer = new Kinetic.Layer();
draw();
}
/*
* INIT
*/
window.onload = function(){
stage = new Kinetic.Stage("container", <?=CANEVAS_WIDTH;?>, <?=CANEVAS_HEIGHT;?>);
stage.on("mousemove", function(){
var mouseInfo = getMouseInfo(stage.getMousePosition());
if(mouseInfo.onMap)
document.body.style.cursor = "pointer";
else
document.body.style.cursor = "default";
});
stage.on("mousedown", function(){
var mouseInfo = getMouseInfo(stage.getMousePosition());
if(mouseInfo.onMap)
changeCursorPosition(mouseInfo.map_x, mouseInfo.map_y);
});
var sources = {
testMap : "testMap.png",
testMapCursor : "testMapCursor.png"
};
loadImages(sources, initStage);
};
Sorry, my english are realy bad.
Thank all.

I know someone who is trying out KineticJS. I haven't used it myself, so I apologize that I cannot provide more specific help.
Unfortunately, it is very difficult to get good performance with canvas, and it depends greatly on the browser. Last I checked, Opera 12 and IE 9 performed significantly faster than other browsers, since their 2D rendering is 3D accelerated (using OpenGL and Direct3D, respectively)
I am not sure if this applies to KineticJS, but one technique you can use to improve performance with canvas is to use multiple canvas elements, and transform their positions rather than blitting on a single surface.
I've been pretty happy with the results I've gotten using Jeash, which is wired into NME's command-line tools. The development is similar to working with Flash, but it will create an HTML5 Canvas application using your code. The same application will also be able to publish to Windows, Mac, Linux, iOS, Android, webOS and Flash, as either native C++ and OpenGL, or as SWF bytecode. This gives you a lot of options for providing the best experience for each user.
http://www.haxenme.org