Mouse position is only read on the first frame - javascript

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.

Related

How can I add a scroll to zoom feature to a bitmap in easelJS?

I am evaluating whether I want to use EaselJS to make a JS image viewer/editor. One necessary feature is the scroll to zoom feature. This means when you have your mouse over a bitmap and you move the scroll wheel, the image scales properly.
I am using the EaselJS drag and drop demo to try scroll to zoom out (https://www.createjs.com/demos/easeljs/draganddrop). I am having trouble finding the event that fires when you move the scroll wheel.
This is the event I tried to add the following event to the bitmap:
bitmap.on("mousewheel", function (evt) {
this.scale = this.scale * 2;
update = true;
});
I also tried the following without success:
bitmap.on("wheel", function (evt) {
this.scale = this.scale * 2;
update = true;
});
and
bitmap.on("scroll", function (evt) {
this.scale = this.scale * 2;
update = true;
});
Here is the demo code in full:
var canvas, stage;
var mouseTarget; // the display object currently under the mouse, or being dragged
var dragStarted; // indicates whether we are currently in a drag operation
var offset;
var update = true;
function init() {
examples.showDistractor();
// create stage and point it to the canvas:
canvas = document.getElementById("testCanvas");
stage = new createjs.Stage(canvas);
// enable touch interactions if supported on the current device:
createjs.Touch.enable(stage);
// enabled mouse over / out events
stage.enableMouseOver(10);
stage.mouseMoveOutside = true; // keep tracking the mouse even when it leaves the canvas
// load the source image:
var image = new Image();
image.src = "../_assets/art/daisy.png";
image.onload = handleImageLoad;
}
function stop() {
createjs.Ticker.removeEventListener("tick", tick);
}
function handleImageLoad(event) {
var image = event.target;
var bitmap;
var container = new createjs.Container();
stage.addChild(container);
// create and populate the screen with random daisies:
for (var i = 0; i < 100; i++) {
bitmap = new createjs.Bitmap(image);
container.addChild(bitmap);
bitmap.x = canvas.width * Math.random() | 0;
bitmap.y = canvas.height * Math.random() | 0;
bitmap.rotation = 360 * Math.random() | 0;
bitmap.regX = bitmap.image.width / 2 | 0;
bitmap.regY = bitmap.image.height / 2 | 0;
bitmap.scale = bitmap.originalScale = Math.random() * 0.4 + 0.6;
bitmap.name = "bmp_" + i;
bitmap.cursor = "pointer";
// using "on" binds the listener to the scope of the currentTarget by default
// in this case that means it executes in the scope of the button.
bitmap.on("mousedown", function (evt) {
this.parent.addChild(this);
this.offset = {x: this.x - evt.stageX, y: this.y - evt.stageY};
});
// the pressmove event is dispatched when the mouse moves after a mousedown on the target until the mouse is released.
bitmap.on("pressmove", function (evt) {
this.x = evt.stageX + this.offset.x;
this.y = evt.stageY + this.offset.y;
// indicate that the stage should be updated on the next tick:
update = true;
});
bitmap.on("rollover", function (evt) {
this.scale = this.originalScale * 1.2;
update = true;
});
bitmap.on("rollout", function (evt) {
this.scale = this.originalScale;
update = true;
});
bitmap.on("mousewheel", function (evt) {
this.scale = this.scale * 2;
update = true;
});
}
examples.hideDistractor();
createjs.Ticker.addEventListener("tick", tick);
}
function tick(event) {
// this set makes it so the stage only re-renders when an event handler indicates a change has happened.
if (update) {
update = false; // only update once
stage.update(event);
}
}
I am expecting the image to scale by a factor of 2 whenever I scroll while the mouse is over a bitmap. Please let me know if anyone has any ideas on how to do this properly.
document.getElementById('canvas').addEventListener('wheel', moverContenido.bind(this));
var i = 0;
function moverContenido(accion) {
if(accion.wheelDelta > 0 || accion.detail > 0) {
i++;
} else if(accion.wheelDelta < 0 || accion.detail < 0) {
i--;
}
}

Trigger an event to call a function that's inside of a closure

I'm working on a project based on a nice little sample canvas drawing app someone else on the project downloaded and modified. We need to allow the user to click a button elsewhere on the page (not part of the canvas), and have it run a function that came with the sample app. However, the function is inside of a closure. Since I can't call the function directly (right? the closure prevents this? I don't often work with closures), I thought I'd be able to accomplish this by triggering a mouse event at the location the user would click to accomplish the same thing. It's not working, and I don't know why not.
I posted a greatly simplified version at this fiddle. Simple HTML code:
<div id="canvasDiv"></div>
<div id="buttonDiv">
<button>why can't I send a click to the canvas?</button>
</div>
And the simplified version of the downloaded sample app, plus my attempt to use jQuery's .trigger method to trigger the event:
var WM = {};
WM.drawingApp = function(options) {
"use strict";
var canvas, context,
// Add mouse and touch event listeners to the canvas
createUserEvents = function() {
var getElementPos = function(element) {
// straight-forward stuff removed for brevity's sake
return pos;
};
var press = function(e) {
// Mouse down location
var sizeHotspotStartX, toolIndex,
mouseX = (e.changedTouches ? e.changedTouches[0].pageX : e.pageX),
mouseY = (e.changedTouches ? e.changedTouches[0].pageY : e.pageY);
var elementPos = getElementPos(document.getElementById(options.canvasElementId || 'canvasDiv'));
mouseX -= elementPos.x;
mouseY -= elementPos.y;
announce(mouseX, mouseY);
};
var announce = function(x,y) { alert('press at: ' + x + ', ' + y); }
// Add mouse event listeners to canvas element
canvas.addEventListener("mousedown", press, false);
},
// Creates a canvas element, etc
init = function() {
// Create the canvas
canvas = document.createElement('canvas');
canvas.setAttribute('width', 100);
canvas.setAttribute('height', 100);
canvas.setAttribute('id', 'canvas');
document.getElementById(options.canvasElementId || 'canvasDiv').appendChild(canvas);
context = canvas.getContext("2d"); // Grab the 2d canvas context
createUserEvents();
};
init();
return {};
};
jQuery(document).ready(function() {
jQuery('#buttonDiv').on('click', 'button', function() {
var down = jQuery.Event("mousedown", {
pageX: 50,
pageY: 50
});
jQuery('#canvasDiv canvas').trigger(down);
});
});
As you can see by running the fiddle, if you click inside the box, you get an alert announcing where you clicked. But if you click the button, you don't get an alert. While writing this question, it occurred to me that maybe jQuery's .trigger method isn't a sufficient way to send the click. Its documentation page specifically says that .trigger "does not perfectly replicate a naturally-occurring event". We're open to solutions that don't involve jQuery.
You can define a variable var press; outside of WM, inside of WM, remove var before press and set press = function() {}. You should then be able to call press(down) at click of button
var press;
press = function(e) {
console.log(e);
// Mouse down location
var sizeHotspotStartX, toolIndex,
mouseX = (e.changedTouches ? e.changedTouches[0].pageX : e.pageX),
mouseY = (e.changedTouches ? e.changedTouches[0].pageY : e.pageY);
var elementPos = getElementPos(
document.getElementById(options.canvasElementId
|| 'canvasDiv')
);
mouseX -= elementPos.x;
mouseY -= elementPos.y;
announce(mouseX, mouseY);
};
jQuery(document).ready(function() {
jQuery('#buttonDiv').on('click', 'button', function() {
var down = jQuery.Event("mousedown", {
pageX: 50,
pageY: 50
});
press(down); // call `press` at `button` click
//jQuery('#canvasDiv canvas').trigger(down);
});
});
// based on http://www.williammalone.com/projects/html5-canvas-javascript-drawing-app-with-bucket-tool/
var press;
var WM = {};
WM.drawingApp = function(options) {
"use strict";
var canvas, context,
// Add mouse and touch event listeners to the canvas
createUserEvents = function() {
var getElementPos = function(element) {
var parentOffset, pos;
if (!element) {
pos = {
x: 0,
y: 0
};
} else {
pos = {
x: element.offsetLeft,
y: element.offsetTop
};
if (element.offsetParent) {
parentOffset = getElementPos(element.offsetParent);
pos.x += parentOffset.x;
pos.y += parentOffset.y;
}
}
return pos;
};
press = function(e) {
console.log(e)
// Mouse down location
var sizeHotspotStartX, toolIndex,
mouseX = (e.changedTouches ? e.changedTouches[0].pageX : e.pageX),
mouseY = (e.changedTouches ? e.changedTouches[0].pageY : e.pageY);
var elementPos = getElementPos(document.getElementById(options.canvasElementId || 'canvasDiv'));
mouseX -= elementPos.x;
mouseY -= elementPos.y;
announce(mouseX, mouseY);
};
var announce = function(x,y) { alert('press at: ' + x + ', ' + y); }
// Add mouse event listeners to canvas element
canvas.addEventListener("mousedown", press, false);
},
// Creates a canvas element, loads images, adds events, and draws the canvas for the first time.
init = function() {
// Create the canvas (Neccessary for IE because it doesn't know what a canvas element is)
canvas = document.createElement('canvas');
canvas.setAttribute('width', 100);
canvas.setAttribute('height', 100);
canvas.setAttribute('id', 'canvas');
document.getElementById(options.canvasElementId || 'canvasDiv').appendChild(canvas);
context = canvas.getContext("2d"); // Grab the 2d canvas context
createUserEvents();
};
init();
return {};
};
jQuery(document).ready(function() {
jQuery('#buttonDiv').on('click', 'button', function() {
var down = jQuery.Event("mousedown", {
pageX: 50,
pageY: 50
});
press(down)
//jQuery('#canvasDiv canvas').trigger(down);
});
});
var drawingApp = WM.drawingApp({
canvasElementId: "canvasDiv"
});
#canvasDiv canvas {
border: solid black 1px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js">
</script>
<div id="canvasDiv"></div>
<div id="buttonDiv">
<button>why can't I send a click to the canvas?</button>
</div>
jsfiddle https://jsfiddle.net/gkvdha3h/5/

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.

Clicakble planets

Im trying to make planets that give an alert message when clicked.
Problem is, onmousedown only works on canvas, as far I tested.
Code for planets:
var planets = [];
for (var b=0;b<3;b++) {
planets.push(planet(0,360,Math.random()*600,Math.random()*600));
}
function planet(I,shiips,xpos,ypos){
I = I||{};
I.ships = shiips;
I.x=xpos;
I.y=ypos;
return I;
}
code for click detection; tests both for planet object and the image
update = function(){
planetImage.onmousedown=function(){alert("works!")};
planets[0].onmousedown=function(){alert("works!")};
}
setInterval(update,100);
Im using canvas to draw the images, if that hhelps.
I found the following code that gives mouse position, but it doesnt work for me:
(function() {
var mousePos;
window.onmousemove = handleMouseMove;
setInterval(getMousePosition, 100); // setInterval repeats every X ms
function handleMouseMove(event) {
event = event || window.event; // IE-ism
mousePos = {
x: event.clientX,
y: event.clientY
};
}
function getMousePosition() {
var pos = mousePos;
if (!pos) {
// We haven't seen any movement yet
}
else {
// Use pos.x and pox.y
}
}
})();
Im trying to keep it simple, I don't really like jquery or anything complicated.
Once again: the problem is onmousedown only works on the canvas object, i.e.
canvas.onmousedown=function(){alert("works!")};
I got it working now with this code:
update = function(){
canvas.onmousedown=function(){
var e = window.event;
var posX = e.clientX;
var posY = e.clientY;
alert("X position: "+ posX + " Y position: " + posY);
};
setInterval(update,100);

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.

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