Develop Reference

passing through and outputting value to console but not drawing on the canvas

There are a few similar questions but none of the answers fix my issue. I am simulating a solar system using canvas. The animation function calls a function to update the positions and then these positions are shown on screen in the form of circles. I have tried not calling the function animate and simply drawing the bodies using the initial conditions and this works fine however when trying to draw them via the animate function nothing is drawn - no even the sun - even though the functions have been passed through.
Why are they not drawing on the canvas?
here is the code (i have removed the for loop which would draw all the planets to only draw the earth just for development purposes, i have also not copied in all the global variables at the top as they take up a lot of space):
var massList = [massMecury, massVenus, massEarth, massMars, massJupiter, massSaturn, massUranus, massNeptune];
var xPosList = [initialMecuryXPos, initialVenusXPos, initialEarthXPos, initialMarsXPos, initialJupiterXPos, initialSaturnXPos, initialUranusXPos, initialNeptuneXPos];
var yPosList = [initialMecuryYPos, initialVenusYPos, initialEarthYPos, initialMarsYPos, initialJupiterYPos, initialSaturnYPos, initialUranusYPos, initialNeptuneYPos];
var xVelList = [initialMecuryXVel, initialVenusXVel, initialEarthXVel, initialMarsXVel, initialJupiterXVel, initialSaturnXVel, initialUranusXVel, initialNeptuneXVel];
var yVelList = [initialMecuryYVel, initialVenusYVel, initialEarthYVel, initialMarsYVel, initialJupiterYVel, initialSaturnYVel, initialUranusYVel, initialNeptuneYVel];
//position and velocity scales so they fit on the screen
var posScale = 1.7E10;
//var velScale = 3E9;
var pauseButtonPressed = false;
function axis (){
var canvas = document.getElementById("solarsys");
c=canvas.getContext('2d');
//moves the origin to the centre of the page
c.translate(400, 275);
//makes the y axis grow up and shrink down
c.scale(1,-1);
//c.fillRect(-innerWidth/2,-innerHeight/2,innerWidth,innerHeight); if want a black background
}
function calAcc(i) {
//calculates distance between the earth and the sun
var r = Math.sqrt((xPosList[i]*xPosList[i]) + (yPosList[i]*yPosList[i]));
//calculates the angle of displacement between the earth and sun
var theta = Math.atan(yPosList[i]/xPosList[i]);
//calculate the force on the earth using F = Gm1m2/r^2
//force is towards the centre of the sun
var F = (G*massSun*massList[i])/(r*r);
//correct the angle based on which quadrant it is in
theta=Math.abs(theta);
if (xPosList[i] < 0 && yPosList[i] < 0){
theta = theta;
} else if (xPosList[i] > 0 && yPosList[i] < 0){
theta = Math.PI-theta;
} else if (xPosList[i] > 0 && yPosList[i] > 0){
theta = theta-Math.PI;
} else{
theta = (2*Math.PI)-theta;
}
var fX = Math.cos(theta)*F;
var fY = Math.sin(theta)*F;
//calculate earths acceleration using Newton 2nd a = F / m
var aX = (fX/massList[i]);
var aY = (fY/massList[i]);
return [aX, aY];
}
function leapfrog(i) {
var dt = 5000;
var a = calAcc(i);
xVelList[i] = xVelList[i] + (a[0]*dt);
yVelList[i] = yVelList[i] + (a[1]*dt);
xPosList[i] = xPosList[i] + (xVelList[i]*dt);
yPosList[i] = yPosList[i] + (yVelList[i]*dt);
}
function drawBody(i) {
c.beginPath();
c.arc(xPosList[i]/posScale, yPosList[i]/posScale, 1, 0, twoPi, false);
c.stroke();
c.closePath();
console.log('body drawn');
}
function drawSun(){
//draw a yellow circle - the sun
c.beginPath();
c.arc(0, 0, 2, 0, twoPi, false);
c.fillStyle = '#ffcc00';
c.fill();
c.stroke();
c.closePath();
}
function animate() {
var i = 2;
//for (var i=0; i< xPosList.length; i++){
leapfrog(i);
drawBody(i);
drawSun();
console.log(xPosList);
//clears canvas each new loop
c.clearRect(-innerWidth/2,-innerHeight/2,innerWidth,innerHeight);
}
window.onload=function() {
axis();
var looper=setInterval(animate,1);}

You have several problems to fix:
You have a setInterval which is executed with pauses of 1 milliseconds. This seems to be too quick and I absolutely do not see any guarantee that your browser will be able to draw the things to be drawn.
In your animate function you draw things, but instantly remove them. You need to clear the canvas first and only then draw things on the canvas.
Your code is very difficult to read, consider refactoring it

How would one go about making this grid clickable?

I've created the grid below using a canvas as well as lines going through it, how would one go about making this grid clickable?
The ideal result would be when I click one of the boxes it turns yellow, and a value inside an array would be changed from 0 to 1. I'm fairly certain I know how to set up a 2D array but that is the general idea. Thanks for any help.
var cellCount=20;
var currentGrid = new Array(cellCount).fill().map(() => new Array(cellCount).fill(0));
var nextGrid = new Array(cellCount).fill().map(() => new Array(cellCount).fill(0));
for(var i=0;i<20;i++){
for(var j=0;j<20;j++){
currentGrid[i][j]=0;
nextGrid[i][j]=0;
}
}
var canvas=document.getElementById('grid');
var ctx=canvas.getContext('2d');
function drawGrid(h,w,id){
for(var x=0;x<w;x++){
ctx.moveTo(0,x*20);
ctx.lineTo(h,x*20);
ctx.lineWidth=1;
ctx.strokeStyle='rgb(211,211,211)';
ctx.stroke();
}
for(var y=0;y<h;y++){
ctx.moveTo(y*20,0);
ctx.lineTo(y*20,w);
ctx.lineWidth=1;
ctx.strokeStyle='rgb(211,211,211)';
ctx.stroke();
}
}
function getPosition(event)
{
if (event.x != undefined && event.y != undefined)
{
x = event.x;
y = event.y;
}
}
canvas.addEventListener("mousedown", getPosition, false);
drawGrid(421,421,'grid');

Looking at the code you provided, it appears there is no loop, meaning there will be no other updates to the grid visually. Also, the draw function appears that it would draw offscreen, as you are multiplying your values by 20, which should probably be cellCount.
First I would recommend setting up a 'game loop'. A pattern that involves updating and drawing in a loop:
function loop(tick) {
update(tick);
draw(tick);
requestAnimationFrame(loop);
}
// start the loop
requestAnimationFrame(loop);
Then you'll need to define the update and draw function. In this example you may not have anything to update yet, but you might in the future. The draw function would first erase the background and then draw the grid:
function draw(tick) {
// clear background
ctx.clearRect(0, 0, canvas.width, canvas.height);
// draw the grid
drawGrid(numCols, numRows);
}
Now you'll need to define numCols and numRows which is simply the width or height divided by the cellSize. This tells you how many cells in the height and width of the canvas. I see you have cellCount instead of cellSize, but cellSize can be calculated the opposite way by taking canvas height (or width) and dividing it by cellCount (assuming the canvas is square).
var numCols = Math.floor(canvas.width / cellSize);
var numRows = Math.floor(canvas.height / cellSize);
As for the click handler; you'll want to figure out which cell they clicked in by dividing the x and y you've captured by the cellSize.
// assuming x and y are the coordinates on the canvas where the user clicked
var cellX = Math.floor(x / cellSize);
var cellY = Math.floor(y / cellSize);
// now set the cell
nextGrid[cellY][cellX] = 1;

Make multiple canvas or overlay drawings on the same canvas html5

I need your advice, I have a html with canvas, in this html you can add circles and then link these to make a figure, I also want to insert a search where you can find the different figures and focussed on it, so I don't know if it'll be better : to overlay the figures or use different canvas for each figure.
(I'm not implement the search function yet.)
What do you think?
Here is the functions that makes de draws
//this function puts the circles on a <table>, and then the other function takes the img coordinates and link it making a figure.
function position(year, mon)
{
$('#' + year + ' .' + mon).prepend('<img class="black_point" src="./images/circle.png"/>');
}
var table = document.getElementById("tabla");
var images = table.getElementsByTagName("img");
var canvas = document.getElementById("miCanvas");
var ctx = canvas.getContext("2d");
var x,y; // Remember coordinates
canvas.width = table.offsetWidth;
canvas.height = table.offsetHeight;
function connect(image, index) { //this function link the images
var tabBcr = table.getBoundingClientRect();
var imgBcr = image.getBoundingClientRect();
x = imgBcr.left + (imgBcr.width / 2) - tabBcr.left;
y = imgBcr.top + (imgBcr.height / 2) - tabBcr.top;
index === 0 ? ctx.moveTo(x, y) : ctx.lineTo(x, y);
}
//this function add a new canvas
function figure(){
/*$('#miCanvas').prepend('<canvas id="myCanvas">Su navegador no soporta Canvas.</canvas>');
//this is the property who overlay the figures
cxt.globalCompositeOperation="source-over";/*
//which it will be better to implement a search function?
}
// new path here
ctx.beginPath();
for(var i=0; i<images.length; i++){
connect( images[i], i); // provide index so we can sep. move/line
}
// then at the end:
ctx.fill();

Use 1 html canvas to hold all your connected circles.
This simplifies the event handling when focusing / blurring your figures.
You can test if the mouse is inside one of your circles like this:
// given a circle defined by centerX, centerY, radius
var dx = mouseX - centerX;
var dy = mouseY - centerY;
var isInside = dx*dx+dy*dy <= radius*radius;
Here's an outline of how to focus on a figure:
Create a javascript object defining each circle. If a set of objects makes up a figure, then add a group property to each circle-object representing which group that circle is a member of.
Put all your circle-objects in an array.
In your mouse event handlers, iterate through the circle-objects-array and find which circle is under the mouse. That circle's group has been focused.

Get coordinates of two different places on HTML canvas

Aim of my code:
Draw a small rectangle on a HTML canvas whenever a user clicks the canvas. The rectangle should have a small number representing the number of rectangles made by the user.
The user should be able to connect any two rectangles using a straight line. (Preferably by just pressing left mouse button, and taking the mouse from first rectangle to second rectangle)
Approach and my attempt
As you can see in this jsFiddle , I have been able to achieve the first part of above very well. On clicking on the canvas, a rectangle with a number inside of it is made. But I am really clueless about the second part.
How do I make the user connect any two made rectangles? I want the connection to be made only if a rectangle is there ( So I would need to store coordinates of every rectangle that has been made, that's okay as I can use an array for that ).
Basically, I just want to check if the mousedown was at one place and mouseup at the other.
How do I get these two different coordinates ( one of mousedown and other of mouseup ) , and draw a line between them?
I have given the Fiddle above but still here's my jquery:
$(function () {
var x, y;
var globalCounter = 0;
$('#mycanvas').on("click", function (event) {
x = event.clientX + document.body.scrollLeft + document.documentElement.scrollLeft;
x -= mycanvas.offsetLeft;
y = event.clientY + document.body.scrollTop + document.documentElement.scrollTop;
y -= mycanvas.offsetLeft;
// alert("x:"+x+"y: "+y);
drawRectangle(x, y);
});
function drawRectangle(x, y) {
var acanvas = document.getElementById("mycanvas");
var context = acanvas.getContext("2d");
context.strokeRect(x, y, 25, 25);
globalCounter++;
writeNo(x, y, globalCounter);
}
function writeNo(x, y, n) {
var acanvas = document.getElementById("mycanvas");
var context = acanvas.getContext("2d");
context.font = "bold 14px sans-serif";
context.fillText(n, x + 8, y + 12.5);
}
});
The main question is therefore: connecting the two made rectangles by mousedrag
How do I achieve this?
Thank You.

How about this: http://jsfiddle.net/4jqptynt/4/
Ok, first I did a little refactoring for your code to make things easier. Just stuff like putting the code that gets the canvas coordinates into it's own function, and caching some variables (like the canvas context) in the outer function's scope. Oh, and defining your rectangle dimensions as constants because we'll be using the same numbers in a couple of different places.
As you said, the first thing we need is to keep track of the existing rectangles using an array rects (easy enough to do within drawRectangle). Then we need a function to check if a particular pair of coordinates are within some rectangle:
function inRectangle(x, y) {
for (var i = 0, l = rects.length; i < l; i++) {
if ((x - rects[i].x) <= RECT_X && (y - rects[i].y) <= RECT_Y &&
(x - rects[i].x) >= 0 && (y - rects[i].y) >= 0) {
return i;
}
}
}
where RECT_X & RECT_Y define the sides of the rectangle. If the coordinates do exist within some rectangle then this will return the index of that rectangle within the rects array.
Then it's a case of checking whether or not a mousedown occurred within a rectangle, noting that inRectangle will only return a number if the mousedown event was within a rectangle:
$acanvas.on("mousedown", function (event) {
var coords = getCoords(event),
rect = inRectangle(coords.x, coords.y);
if (typeof rect === "number") {
dragStart = rect + 1;
} else {
drawRectangle(coords.x, coords.y);
}
});
if so, make a note of which rectangle using dragStart, if not draw a rectangle as before.
Then to complete the drag, we need to attach a handler to mouseup:
$acanvas.on("mouseup", function (event) {
if (!dragStart) { return; }
var coords = getCoords(event),
rect = inRectangle(coords.x, coords.y);
if (typeof rect === "number") {
drawConnection(dragStart - 1, rect);
}
dragStart = 0;
});
If no drag was started, then it does nothing. If it's coordinates aren't within a rectangle, then it does nothing but reset dragStart. If however, it is within a rectangle, then it draws a connecting line:
function drawConnection(rect1, rect2) {
context.strokeStyle = "black";
context.lineWidth = 1;
context.beginPath();
context.moveTo(rects[rect1].x + RECT_X/2, rects[rect1].y + RECT_Y/2);
context.lineTo(rects[rect2].x + RECT_X/2, rects[rect2].y + RECT_Y/2);
context.stroke();
context.closePath();
}

Canvas - bullets to mouse point

So I'm trying to implement shooting, and what I want to do is take the players x and y and use that as the base point where the projectile derives from and then it basically goes to the point pressed in the canvas. The projectile is deriving from the player, but instead of going to the cursor point it strangely ALWAYS goes right, but will go right+up or right+down depending on which direction was pressed; I've looked on-line and can't seem to find the answer.
Inside my javascript here is the shoot function:
function shoot(event){
bullets[bulletCount] = new Array(4);
bullets[bulletCount][0] = x;
bullets[bulletCount][1] = y;
bullets[bulletCount][2] = window.event.clientX;
bullets[bulletCount][3] = window.event.clientY;
bulletCount++;
}
In my javascript here is the bullet part in the update method:
for(var b = 0; b < bullets.length; b++){
if(bullets[b][0] < bullets[b][2]) bullets[b][0] += 5;
if(bullets[b][0] > bullets[b][2]) bullets[b][0] -= 5;
if(bullets[b][1] < bullets[b][3]) bullets[b][1] += 5;
if(bullets[b][1] > bullets[b][3]) bullets[b][1] -= 5;
ctx.fillRect(bullets[b][0],bullets[b][1], 8, 8);
}
and in my index.html page:
<canvas id="gameBoard" onClick="shoot(event)" width="500" height="500" tabindex="1"></canvas>
EDIT: fixed the problem, for anyone else who suffers this problem inside the shoot function change from what was originally up there to this:
function shoot(event){
var rect = canvas.getBoundingClientRect();
bullets[bulletCount] = new Array(4);
bullets[bulletCount][0] = x;
bullets[bulletCount][1] = y;
bullets[bulletCount][2] = event.clientX - rect.left;
bullets[bulletCount][3] = event.clientY - rect.top;
bulletCount++;
}

The problem lies within these two lines:
bullets[bulletCount][2] = window.event.clientX;
bullets[bulletCount][3] = window.event.clientY;
It is because that the location you save for the click is not the real location.
You see, event.clientX/Y give you the mouse coordinates relative to the top left corner of the window, but you only want the coordinates relative to the top left corner of your canvas element.
To fix this, first get to know another way to get the mouse coordinates, which is event.pageX/Y.
This will not give you the coordinates relative to the canvas, however you need this instead of event.clientX/Y because it will give you the mouse coordinates relative to the top left corner of the page, not the window, which means it doesn't matter if the user scrolls somewhere, the coordinates are always true to the page.
So, now that you're using event.pageX/Y, how to make it relative to the canvas? Well, we can just take these coordinates and subtract the top left corner coordinates of the canvas:
bullets[bulletCount][2] = window.event.pageX - canvas.offsetLeft;
bullets[bulletCount][3] = window.event.pageY - canvas.offsetTop;
Assuming that your canvas element is saved in a variable named canvas
Hope that solves it :D

var bullets = [];
var bullet_speed = 10;
call this in your init() fucntion: which could have your setInterval.
window.addEventListener('click', shoot, false);
call this in your draw function:
for (var i = 0; i < bullets.length; i++){
bullets[i].x += bullets[i].xChange;
bullets[i].y += bullets[i].yChange;
context.fillStyle ='black';
context.fillRect(bullets[i].x,bullets[i].y,4,4)
}
function shoot(event){
x = event.offsetX
y = event.offsetY
d = Math.sqrt(Math.pow(Math.abs(player.x-x),2)+Math.pow(Math.abs(player.y-y),2))
bullet = {
x : player.x,
y : player.y,
xChange : (x-player.x)/(d/bullet_speed),
yChange : (y-player.y)/(d/bullet_speed),
};
bullets.push(bullet);
}