Develop Reference

Colliding with objects(walls) [duplicate]

This question already has answers here:
JavaScript: Collision detection
(10 answers)
Closed 2 years ago.
What a good practice to detect collision of 2 objects(walls). Yes, not just detection, but further displacement so that objects do not enter each other. That is, so that when they collide, they rest against each other, but do not enter.
CODE
class WallObj {
constructor(obj) {//x, y, w, h, bern ,thru) {
this.x = obj.x
this.y = obj.y
this.w = obj.w
this.h = obj.h
this.bern = obj.bern
this.thru = obj.thru
this.hide = obj.hide
this.id = obj.id
}
collusionWall(startPosition, endPosition) {
var xS = startPosition[0]
var x = endPosition[0]
if (xS - x > 0)
if (x)
// if wall behind point
if (this.x < startPosition[0])
return endPosition
else if (this.x + this.w < x)
return endPosition
return endPosition
// return [this.x, endPosition[1]]
}
}

a naive approach would be to check x and y :
let ctx = mycan.getContext("2d");
let objects = [];
class player
{
constructor()
{
this.position = {x:50,y:50};
this.color = "blue";
this.size = 32;
this.stop= false;
this.prevpos=this.position;
window.addEventListener("keydown",(e)=>{
if(this.stop) this.position=this.prevpos;
else this.displacement(e);
});
}
displacement(e)
{
this.prevpos = this.position;
this.position.x+=(e.key=="ArrowRight");
this.position.x-=(e.key=="ArrowLeft");
this.position.y+=(e.key=="ArrowDown");
this.position.y-=(e.key=="ArrowUp");
}
draw()
{
ctx.fillStyle = this.color; ctx.fillRect(this.position.x,this.position.y,this.size,this.size);
}
};
class wall
{
constructor(posx,posy)
{
this.position = {x:posx,y:posy};
this.color = "red";
this.size = 32;
}
draw(){
ctx.fillStyle = this.color;
ctx.fillRect(this.position.x,this.position.y,this.size,this.size);
}
};
for(let i = 0; i<mycan.width;i+=32)
{
objects.push(new wall(i,0));
objects.push(new wall(i,mycan.height-32));
}
for(let j = 0; j<mycan.height;j+=32)
{
objects.push(new wall(0,j));
objects.push(new wall(mycan.width-32,j));
}
let playr=new player;
let collision = (colider)=>{
let colx = false;
let coly = false;
/*******************************************************
here we check if the top left point from our current
wall object is inferior to the top left point of our
player and if the top rignt point of the wall object is
superior to the player top left point.
we need to repeat this for the player top right point
(so we compare the player top right point is superior
to the wall top left point and inferior to the wall
top right point)
then we repeat this for y
*******************************************************/
for(let object of objects)
{
colx = (
(
(object.position.x<=colider.position.x) &&
(
(object.position.x+object.size)>=
(colider.position.x)
)
)||(
(
(colider.position.x+colider.size)>=object.position.x) &&
(
(colider.position.x+object.size)<=(object.position.x+object.size)
)
)
)
coly = (
(
(object.position.y<=colider.position.y) &&
(
(object.position.y+object.size)>=
(colider.position.y)
)
)||(
(
(colider.position.y+colider.size)>=object.position.y) &&
(
(colider.position.y+object.size)<=(object.position.y+object.size)
)
)
)
if(colx&&coly) return true;
}
return false;
};
setInterval(()=>{
ctx.clearRect(0,0,mycan.width,mycan.height);
playr.stop = collision(playr);
playr.draw();
for(let obj of objects)
obj.draw();
},1000/30);
<canvas id="mycan" width=400 height=250></canvas>
à better approach would be to cut your 2d world into zones where the density of objects that can collide is more or less important (a quadtree).
like so :
and an easier way would be to look if the colided object is in a sphere (this would mean that walls have a spheric collision and could hardly be represented as a square) but we could just say that the player is a sphere and check if something has entered his radius.
https://studiofreya.com/3d-math-and-physics/sphere-vs-aabb-collision-detection-test/

Issues with keyIsDown() in p5js

I'm trying to make a basic 2d game with p5js and p5.play. An issue that seems to cause issues every time I try to do anything is the keyIsDown function. Is there a way to determine if a key is down before pressing it? If I used
upKey = keyIsDown(UP_ARROW);
upKey will show as undefined until I press the up arrow. Is there any way to assign the respective boolean values to these types of things prior to pressing them?
As of now, my game will not properly work until I have pressed every involed key one time.

The keyIsDown() function checks if the key is currently down, i.e. pressed. It can be used if you have an object that moves, and you want several keys to be able to affect its behaviour simultaneously, such as moving a sprite diagonally.
Note that the arrow keys will also cause pages to scroll so you may want to use other keys for your game.. but if you want to use arrow keys this is the code snippet from the reference page
let x = 100;
let y = 100;
function setup() {
createCanvas(512, 512);
}
function draw() {
if (keyIsDown(LEFT_ARROW)) {
x -= 5;
}
if (keyIsDown(RIGHT_ARROW)) {
x += 5;
}
if (keyIsDown(UP_ARROW)) {
y -= 5;
}
if (keyIsDown(DOWN_ARROW)) {
y += 5;
}
clear();
fill(255, 0, 0);
ellipse(x, y, 50, 50);
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.7.3/p5.min.js"></script>
To implement similar logic without the use of arrow keys you will need to determine the key code of the keys you want to use.
Here is an example that uses awsd keys and also logs out the key code of the currently pressed key.
let x = 50;
let y = 50;
function setup() {
createCanvas(512, 512);
}
function keyPressed(){
console.log(keyCode);
}
function draw() {
if (keyIsDown(65)) {
x -= 5;
if (x < 0) x = 0;
}
if (keyIsDown(68)) {
x += 5;
if (x > width) x = width;
}
if (keyIsDown(87)) {
y -= 5;
if (y < 0) y = 0;
}
if (keyIsDown(83)) {
y += 5;
if ( y > height) y = height;
}
clear();
fill(255, 0, 0);
ellipse(x, y, 50, 50);
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.7.3/p5.min.js"></script>

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.

Why do my laser rays flicker?

I'm trying my hands at some simple game programming in Javascript and have come to realize I need to change the way I handle sprites. The only question is, "how"?
I have a hero that moves around with the arrow keys and fires laser rays with WASD. This is how I define rays:
function Ray (x, y, width, height, direction, index) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
this.direction = direction;
this.index = index;
this.speed = 512;
this.disabled = false;
}
The index just indicates where in an array of rays (heh) it is being stored. I currently have a hard-coded limit of 5 simultaneous rays, although the other restrictions (screen size, ray size, speed, hero size etc) shouldn't allow for more than 4:
var rays = [];
var numberOfRays = 0;
var rayLimit = 5;
var shotClock = 300;
And so, in the update() function that gets called by the game loop, I have listeners for the WASD keys. They look like this:
// D
if (68 in keysDown && numberOfRays <= rayLimit && Date.now() - lastShootTime > shotClock) {
lastShootTime = Date.now();
var newRayIndex = findFreeRay();
rays[newRayIndex] = new Ray(hero.x + hero.width + 12, hero.y + hero.height / 2, rayImage.width, rayImage.height, 'right', newRayIndex);
numberOfRays++;
}
(findFreeRay() just returns the lowest unused or disabled (off the screen) index in rays[])
Earlier in the update() method (I have also tried putting it later) I have the logic for updating ray movement:
rays.forEach(function(ray) {
if (ray != null && !ray.disabled) {
switch(ray.direction) {
case 'right':
ray.x += ray.speed * modifier;
break;
case 'left':
ray.x -= ray.speed * modifier;
break;
case 'up':
ray.y -= ray.speed * modifier;
break;
case 'down':
ray.y += ray.speed * modifier;
break;
}
}
});
Finally, there is the image for the ray (actually, one for horizontal rays and another one for vertical rays). Currently, I am using one Image object of each globally, that the existing rays share. But I have also tried, without much luck, to create individual image objects for every ray.
// Ray images
var rayReady = false;
var rayImage = new Image();
rayImage.onload = function() {
rayReady = true;
};
rayImage.src = "images/ray.png";
var rayVertReady = false;
var rayVertImage = new Image();
rayVertImage.onload = function() {
rayVertReady = true;
};
rayVertImage.src = "images/ray_vert.png";
And here is how they get drawn:
if (rayReady && rayVertReady && numberOfRays > 0) {
rays.forEach(function(ray) {
if (ray.x > canvas.width
|| ray.x + ray.width < 0
|| ray.y > canvas.height
|| ray.y + ray.height < 0) {
numberOfRays--;
ray.disabled = true;
}
else if (ray.direction == 'right' || ray.direction == 'left'){
ctx.drawImage(rayImage, ray.x, ray.y);
}
else {
ctx.drawImage(rayVertImage, ray.x, ray.y);
}
});
}
The problem
After shooting only a few rays, new ones start to either flicker and disappear, or stay invisible altogether. They actually exist as gameplay objects though, as they can hit targets.
What likely causes this flickering?
(credit to Matt Hackett for the base of this code)
fiddle: http://jsfiddle.net/Vr3MW/

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.