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Make canvas line show

Ok, here is something simple, I hope. I've a div container in which I can click and what I'm trying to do is to create two perpendicular lines which cross each other where I've clicked. So far I've written those:
#fr{
float: right;
margin-top: 5%;
height: 720px;
width: 1280px;
position: relative;
background-image: url(blueboard.jpg);
border: 1px solid black;
clear:none;
}
canvas{
border:1px solid red;
float: right;
height: 720px;
width: 1280px;
clear:none;
}//css part, I actually place the canvas on top of my div
//and on html...
<canvas id="line"></canvas>
//js
function saveOO(e){
var xo, yo;
xo=e.clientX;
yo=e.clientY;
...
document.getElementById("saved").innerHTML="The (0;0) = " +"("+xo+";"+yo+")";
document.getElementById("ball").style.left=xo+'px';
document.getElementById("ball").style.top=yo+'px';
xylines(xo, yo);
...;
}
function lines(xo, yo){
var xo, yo, xl, xline, yl, yline, Dx, Dy, a, b, c, d, e;
xo=xo;
yo=yo;
a=$("#fr").position();
b=$("#fr").width();
c=$("#fr").height();
Dy=a.top+100;
Dx=a.left;
d=Dx+b;
e=Dy+c;
xline = document.getElementById("line");
xl=xline.getContext("2d");
xl.beginPath();
xl.moveTo(Dx,yo);
xl.lineTo(d,yo);
xl.lineWidth = 15;
xl.stroke();
yline = document.getElementById("line");
yl=yline.getContext("2d");
yl.beginPath();
yl.moveTo(xo,Dy);
yl.lineTo(xo,e);
yl.lineWidth = 15;
yl.stroke();}
I have, as well, checked whether all variables assign a value and everything is good with that. The crossing point should be exactly where the blue ball is, it also positions on the place where it's clicked. As you can see on the image no lines show, even if I remove the blue background. Please, help me, maybe something is missing. I'm looking forward to your answers.
:)
P.S. Dy is Y of the top left corner, Dx respectively X of the top left corner

Update 2
A slightly amended fiddle where the lines span the entire width/height of the canvas:
https://jsfiddle.net/0y37qwvw/5/
This is by using 0 as the starting point for each and canvas.width/canvas.height as the ending point.
Update
Here is a fiddle demonstrating the use of a canvas overlay and responding to a click events.
https://jsfiddle.net/0y37qwvw/4/
The important thing is to get the relative x and y co-ordinates right, which I have done using event.offsetX and event.offsetY and a fallback for when they are not implemented:
document.getElementById("canvas-overlay").addEventListener("click", function( event ) {
var x, y, clientRect;
clientRect = event.target.getBoundingClientRect();
x = (typeof event.offsetX !== 'undefined' ? event.offsetX : (event.clientX - clientRect.left));
y = (typeof event.offsetY !== 'undefined' ? event.offsetY : (event.clientY - clientRect.top));
lines(x, y, 50, 50);
}, false);
Original answer
Your code is incomplete, so it is hard to be sure what the exact problems are.
One problem though is that you have not directly set the width and height of the canvas element, which will result in the canvas being scaled.
You can do this on the canvas element:
<canvas id="line" height="720" width="1280"></canvas>
Demonstrated at:
https://jsfiddle.net/0y37qwvw/1/
You could also set the width and height programmatically:
var canvas = document.getElementById("line");
canvas.width = 1280;
canvas.height = 720;
https://jsfiddle.net/0y37qwvw/3/
Compare to what happens if the width and height are only set by CSS:
https://jsfiddle.net/0aph7yno/
If you still can't get it to work, set up a plunker/fiddle with the broken code.

Here is some code I have written, I tried to use as much as OOP style so it's easier to expand it. But still simple and clear.
http://jsfiddle.net/eeqhc2tn/2/
var canvas = document.getElementById('can');
var ctx = canvas.getContext('2d');
var drawThese = [];
canvas.width = 500;
canvas.height = 500;
render();
//Line Code
function Line(sx, sy, ex, ey) {
this.sx = sx;
this.sy = sy;
this.ex = ex;
this.ey = ey;
}
Line.prototype.draw = function () {
ctx.beginPath();
ctx.moveTo(this.sx, this.sy);
ctx.lineTo(this.ex, this.ey);
ctx.stroke();
};
Line.drawCrossLines = function (x, y) {
var horizontal = new Line(0, y, canvas.width, y);
var vertical = new Line(x, 0, x, canvas.height);
drawThese.push(horizontal);
drawThese.push(vertical);
}
canvas.addEventListener('click', function (e) {
Line.drawCrossLines(e.offsetX, e.offsetY);
});
//Circle code
function Circle(x, y, r) {
this.x = x;
this.y = y;
this.r = r;
}
Circle.prototype.draw = function () {
ctx.beginPath();
ctx.arc(this.x, this.y, this.r, 0, 2 * Math.PI);
ctx.fill();
};
//Moving Circle Code that extends Circle
function MovingCircle() {
Circle.call(this,0,0,10);
}
MovingCircle.prototype = Object.create(Circle.prototype);
MovingCircle.prototype.constructor = MovingCircle;
MovingCircle.prototype.move = function (x, y) {
this.x = x;
this.y = y;
}
var pointer = new MovingCircle();
drawThese.push(pointer);
canvas.addEventListener('mousemove',function(e){
pointer.move(e.offsetX, e.offsetY);
});
//Rendering and animation code
function render() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawThese.forEach(function (e) {
e.draw();
});
requestAnimationFrame(render);
}

I've found a working solution on my own, of course inspired by rpn. If you would like to make same or similar thing to what I this topic is about, a system including a container, canvas and a mouse event (click, in this case) you will have to follow this steps.
1. You cannot draw directly to a div, you've to create something like an invisible overlay for canvas and to place it perfectly over the div.
2. An important part is getting the proper coordinates, take into account that there are some tad but important differences between the various coords get methods. (`clientX/Y`, `offsetX/Y` and so on). It matters a lot.
3. Last but not at least, you should carefully consider how you get container's dimensions, as you'll need them later. Remember! We are in a container, a.k.a. working with an area which is just part of the whole window (your browser).
At first I was receiving my coordinates with clientX/Y but maybe due to some mismatches between the get method for coordinates and the one for div's dimensions I was hammered by bugs. To solve this, I've created a method from which I take mouse click coordinates with offsetX/Y. This way you have to think of you container as if it is a separate coordinate system, different from your window's(which by default is general). This means that now the top left corner of this div has x:y = (0;0);
function getcooords(){
xo = e.offsetX;
yo = e.offsetY;
DrawLines(x0, y0); //invoke func DrawLines
}
Now we go to the moment where we should draw our lines.
function DrawLines(x0,y0){
//your variables here...
w=$("#yourcontainer").width();
h=$("#yourcontainer").height();
Dy=0;
Dx=0;
}
That's the second step, Dx and Dy are the top and left properties of the div. Hence, from the what I've just said above, they will be equal to 0, both. Width and height of the container I take simply with jq but you can do it on another preferred way.
Generally speaking, that's the core of your drawing algorithm after we've taken needed dimensions and coordinates:
xl.beginPath();
xl.moveTo(b,yo);//start point of line
xl.lineTo(Dx,yo);//end point of line
xl.stroke(); //DRAW IT :)
Now, I've forgot to tell you that you have to define your lines at first, where should they be, what properties, styles should they have, etc..:
var xline = document.getElementById("line");
xl=xline.getContext("2d");
Remember! If you would like to delete, to erase the what you've drawn you'd have to define your lines FIRST and delete them after their definition. I'm saying definition, not drawing and you can draw the next 1, 2, 3... n lines and delete them over and over again if you follow this principle.
That's it guys, I hope I've explained it well, sorry for my English, probably I've made some tad mistakes but I hope you understand me. If you have any questions, please feel free to ask me, I'll try to do my best in order to help you.
:)

Moving image in canvas with mouse

I have this canvas where I use 2 pictures, one is the main picture and the second picture is used as a clipping mask.
I need to be able to move the main picture and have the code already implemented, but when we click in the picture to drag, the image always assumes the initial position, and also when we drag the image it doesn't move along with the mouse, there's some kind of increasing delay. I tried to turn around this, but I'm not that good with math to come up with the right formula.
This is the code I use to capture the mouse moving:
$(window).mousemove(function(event) {
if( isDragging == true )
{
var cWidth = $("#stcanvas").width();
moveXAmount = (event.pageX / $(window).width())*cWidth;
moveXAmount = moveXAmount - (cWidth/2);
var cHeight = $("#stcanvas").height();
moveYAmount = (event.pageY / $(window).height())*cHeight;
moveYAmount = moveYAmount - (cHeight/2);
buildcanvas();
}
});
Any idea how can this be solved?
Here is a fiddle: http://jsfiddle.net/rVx5G/10/

It looks like you need to handle the delta in mouse movements instead of moving relative to window. Here is a jsfiddle. The change is:
var prevX = 0;
var prevY = 0;
$(window).mousemove(function(event) {
if( isDragging == true )
{
if( prevX>0 || prevY>0)
{
moveXAmount += event.pageX - prevX;
moveYAmount += event.pageY - prevY;
buildcanvas();
}
prevX = event.pageX;
prevY = event.pageY;
}
});
Does that achieve what you wanted?

Change this line like below for auto size
ctx.clearRect(0, 0, mask_image.width, mask_image.height);
function make_pic(ctx) {
// Mask for clipping
mask_image = new Image();
mask_image.src = 'mask.png';
ctx.clearRect(0, 0, mask_image.width, mask_image.height);
ctx.drawImage(mask_image, 0, 0);
ctx.save();
....

cancelAnimationFrame for Animation on Javascript

Hello I'm trying to create a rectangle that grows from the side of the canvas until it fills the whole canvas, once it has done that shrink back to is original state, the approach I'm taking is using requestAnimationFrame /cancelAnimationFrame for some reason I'm not sure cancelAnimationFrame does not seem to work my code is the following one :
<script>
function grRectangle(){
var canvas = document.getElementById("paper");
var context= canvas.getContext("2d");
//var forpi = Math.PI * 2;
//context.fillStyle = "black";
context.fillRect(0,0,canvas.width,canvas.height);
var posX = 200;
var posY = 100;
var color = 0;
function draw(){
context.fillStyle = 'hsl('+ color++ + ',100%,50%)';
context.beginPath();
context.rect(0,0,posX,posY);
context.fill();
posX = posX + 0.9;
posY = posY + 0.9;
if(posX < canvas.width ){
requestAnimationFrame(draw);
} if (posX >= canvas.width){
posX = posX - 0.9;
posY = posY - 0.9;
cancelAnimationFrame(draw);
}
}
draw();
};
</script>
<body onload= "grRectangle();" >
<h1>Growing Rectangle</h1>
<canvas id = "paper" width="800" height="600">
</canvas>
Any help is kindly appreciatted

It seems to me like the code you wrote doesn't actually need a cancelAnimationFrame. I am not sure what you think it does exactly, but it seems like you misunderstood it.
The cancelAnimationFrame method is used to prevent a previous call to requestAnimationFrame from getting executed, as long as this didn't happen yet. There are really few situations where you need this.
In your case I would put that growth-per-frame constant of 0.9 into a variable. When the rectangle size reaches the upper bound, just change it to -0.9 and it will get smaller again. When it reaches the lower bound, change it again to 0.9 and it will grow again.
You will, however, not see that shrinking, because you aren't erasing your canvas. Every frame is drawn on top of the previous one. You will have to erase your canvas at the beginning of your drawing loop. To do that, move the code which fills the canvas with a black rectangle into the drawing loop (remember to set the fill-style to black).

HTML5 canvas character jump

I try to make an animation of character by reading this tutorial:
http://mrbool.com/html5-canvas-moving-a-character-with-sprites/26239 .
It's quite ease to make the character go left ('go right' is already done). But how to make the character jump (with animation)?
I was thinking about something like this:
case 38:
if (y + dy > HEIGHT){
y += dy
}
break;
...but it just move character up (without animation). Can someone help me? Some code example will be useful.

You get the jumping behavior like this (using the same code on the tutorial)
JSFiddle
var canvas;// the canvas element which will draw on
var ctx;// the "context" of the canvas that will be used (2D or 3D)
var dx = 50;// the rate of change (speed) horizontal object
var x = 30;// horizontal position of the object (with initial value)
var y = 150;// vertical position of the object (with initial value)
var limit = 10; //jump limit
var jump_y = y;
var WIDTH = 1000;// width of the rectangular area
var HEIGHT = 340;// height of the rectangular area
var tile1 = new Image ();// Image to be loaded and drawn on canvas
var posicao = 0;// display the current position of the character
var NUM_POSICOES = 6;// Number of images that make up the movement
var goingDown = false;
var jumping;
function KeyDown(evt){
switch (evt.keyCode) {
case 39: /* Arrow to the right */
if (x + dx < WIDTH){
x += dx;
posicao++;
if(posicao == NUM_POSICOES)
posicao = 1;
Update();
}
break;
case 38:
jumping = setInterval(Jump, 100);
}
}
function Draw() {
ctx.font="20px Georgia";
ctx.beginPath();
ctx.fillStyle = "red";
ctx.beginPath();
ctx.rect(x, y, 10, 10);
ctx.closePath();
ctx.fill();
console.log(posicao);
}
function LimparTela() {
ctx.fillStyle = "rgb(233,233,233)";
ctx.beginPath();
ctx.rect(0, 0, WIDTH, HEIGHT);
ctx.closePath();
ctx.fill();
}
function Update() {
LimparTela();
Draw();
}
var Jump = function(){
if(y > limit && !goingDown){
y-=10;
console.log('jumping: ' + y);
} else{
goingDown = true;
y +=10;
if(y > jump_y){
clearInterval(jumping);
goingDown = false;
}
}
}
function Start() {
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
return setInterval(Update, 100);
}
window.addEventListener('keydown', KeyDown);
Start();

There's no one right answer to this question, and unless you find a game-design library, there's no simple one, either. Your problem is that you're moving the character instantaneously in response to input, but a jump requires movement over time. You'll have to either find a moving sprites library - I don't have one in particular to recommend, but I'm sure Google has several - or set up something yourself that runs every so many milliseconds and updates the character's position and some sort of velocity variable.
Edit: Looking at that tutorial, the simplest solution that comes to mind is to put your animation code inside of Update(), like so:
function Update() {
LimparTela();
Animate();
Draw();
}
Inside of Animate(), you should keep track of the character's height and vertical momentum. If the momentum is positive, increase the y position a little, otherwise decrease it a little. Either way, reduce momentum a bit. Add something to keep the character from going through the floor, and have the up key set the character's momentum to be positive if he's on the floor.
Note that this is an incredibly bare-bones solution, but for a basic tutorial it'll do the job.

html 5 canvas javascript rain animation(how to implement efficiently and easily!)

I tried both of these in canvas and nothing showed, also I doubt it is even efficient :/. I am trying to make rain that comes down the screen.. Wondering what is the most efficient way of doing this. I am a beginner at animation and would really appreciate help.
I suspect that creating a rain object would be best, each with the quality of coming down the screen then coming to the top and then an array with them...maybe with random x values withing the canvas width and y values of 0 but I don't know how to implement that. Please help!
xofRain = 20;
startY = 0;
ctx.beginPath();
ctx.moveTo(xofRain, startY);
ctx.lineTo(xofRain, startY + 20);
ctx.closePath();
ctx.fillStyle = "black";
ctx.fill();
function rain(xofRain){
startY = canvas.height();
ctx.moveTo(xofRain, startY);
ctx.beginPath();
ctx.lineTo(xofRain, startY + 3);
ctx.closePath();
ctx.fillStyle = "blue";
ctx.fill();
}

Here comes your answer, this snow rain is created using pure HTML5 Canvas, the technique used to achieve this animation is called "Double Buffer Animation". First it is good to know what is Double Buffer animation technique.
Double Buffer Technique: This is an advanced technique to make animation clear and with less flickers in it. In this technique 2 Canvas is used, one is displayed on webpage to show the result and second one is used to create animation screens in backed process.
How this will help full, suppose we have to create a animation with very high number of move, as in our Snow Fall example, there are number of Flakes are moving with there own speed, so keep them moving, we have to change position of each flake and update it on the canvas, this is quite heavy process to deal with.
So Now instead of updating each Flake directly on our page canvas, we will create a buffer Canvas, where all these changes take place and we just capture a Picture from Buffer canvas after 30ms and display it on our real canvas.
This way our animation will be clear and without flickers. So here is a live example of it.
http://aspspider.info/erishaan8/html5rain/
Here is the code of it:
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>HTML5 Rain</title>
<!--[if IE]>
<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<style>
article, aside, figure, footer, header, hgroup,
menu, nav, section { display: block; }
</style>
<script type="text/javascript">
var canvas = null;
var context = null;
var bufferCanvas = null;
var bufferCanvasCtx = null;
var flakeArray = [];
var flakeTimer = null;
var maxFlakes = 200; // Here you may set max flackes to be created
function init() {
//Canvas on Page
canvas = document.getElementById('canvasRain');
context = canvas.getContext("2d");
//Buffer Canvas
bufferCanvas = document.createElement("canvas");
bufferCanvasCtx = bufferCanvas.getContext("2d");
bufferCanvasCtx.canvas.width = context.canvas.width;
bufferCanvasCtx.canvas.height = context.canvas.height;
flakeTimer = setInterval(addFlake, 200);
Draw();
setInterval(animate, 30);
}
function animate() {
Update();
Draw();
}
function addFlake() {
flakeArray[flakeArray.length] = new Flake();
if (flakeArray.length == maxFlakes)
clearInterval(flakeTimer);
}
function blank() {
bufferCanvasCtx.fillStyle = "rgba(0,0,0,0.8)";
bufferCanvasCtx.fillRect(0, 0, bufferCanvasCtx.canvas.width, bufferCanvasCtx.canvas.height);
}
function Update() {
for (var i = 0; i < flakeArray.length; i++) {
if (flakeArray[i].y < context.canvas.height) {
flakeArray[i].y += flakeArray[i].speed;
if (flakeArray[i].y > context.canvas.height)
flakeArray[i].y = -5;
flakeArray[i].x += flakeArray[i].drift;
if (flakeArray[i].x > context.canvas.width)
flakeArray[i].x = 0;
}
}
}
function Flake() {
this.x = Math.round(Math.random() * context.canvas.width);
this.y = -10;
this.drift = Math.random();
this.speed = Math.round(Math.random() * 5) + 1;
this.width = (Math.random() * 3) + 2;
this.height = this.width;
}
function Draw() {
context.save();
blank();
for (var i = 0; i < flakeArray.length; i++) {
bufferCanvasCtx.fillStyle = "white";
bufferCanvasCtx.fillRect(flakeArray[i].x, flakeArray[i].y, flakeArray[i].width, flakeArray[i].height);
}
context.drawImage(bufferCanvas, 0, 0, bufferCanvas.width, bufferCanvas.height);
context.restore();
}
</script>
</head>
<body onload="init()">
<canvas id="canvasRain" width="800px" height="800px">Canvas Not Supported</canvas>
</body>
</html>
Also if you find this help full, accept as Answer and make it up. o_O
Cheers!!!

I'm not sure what "most efficient" is. If it was me I'd do it in WebGL but whether or not that's efficient is not clear to me.
In either case I'd try to use a stateless formula. Creating and updating state for every raindrop is arguably slow.
const ctx = document.querySelector("canvas").getContext("2d");
const numRain = 200;
function render(time) {
time *= 0.001; // convert to seconds
resizeCanvasToDisplaySize(ctx.canvas);
const width = ctx.canvas.width;
const height = ctx.canvas.height;
ctx.fillStyle = "black";
ctx.fillRect(0, 0, width, height);
resetPseudoRandom();
const speed = time * 500;
ctx.fillStyle = "#68F";
for (let i = 0; i < numRain; ++i) {
const x = pseudoRandomInt(width);
const y = (pseudoRandomInt(height) + speed) % height;
ctx.fillRect(x, y, 3, 8);
}
requestAnimationFrame(render);
}
requestAnimationFrame(render);
let randomSeed_ = 0;
const RANDOM_RANGE_ = Math.pow(2, 32);
function pseudoRandom() {
return (randomSeed_ =
(134775813 * randomSeed_ + 1) %
RANDOM_RANGE_) / RANDOM_RANGE_;
};
function resetPseudoRandom() {
randomSeed_ = 0;
};
function pseudoRandomInt(n) {
return pseudoRandom() * n | 0;
}
function resizeCanvasToDisplaySize(canvas) {
const width = canvas.clientWidth;
const height = canvas.clientHeight;
if (canvas.width !== width || canvas.height !== height) {
canvas.width = width;
canvas.height = height;
}
}
body { margin: 0; }
canvas { width: 100vw; height: 100vh; display: block; }
<canvas></canvas>
Note that I could have used ctx.moveTo(x, y); ctx.lineTo(x, y + 8); for each line and then at the end of the loop called ctx.stroke(). I didn't do that because I'm assuming it would be less efficient than using ctx.fillRect. In order for the canvas to draw lines it actually has to allocate a dynamic path (you call ctx.beginPath). It then has to record all the lines you add. Then it has to expand those lines into vertices of various kinds to rasterize the lines. You can basically see the various algorithms it uses here. Conversely none of that has to happen with ctx.fillRect. No allocations have to happen (not saying they don't happen, just saying they don't have to). The canvas can just use a single pre-allocated quad and draw it on the GPU by passing the correct matrix to draw whatever rectangle you ask of it. Of course they're might be more overhead calling ctx.fillRect 200 times rather than ctx.moveTo, ctx.lineTo 200s + ctx.stroke once but really that's up to the browser.
The rain above may or may not be a good enough rain effect. That wasn't my point in posting really. The point is efficiency. Pretty much all games that have some kind of rain effect do some kind of stateless formula for their rain. A different formula would generate different or less repetitive rain. The point is it being stateless.