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Making a drawing app inside a bootstrap modal

I am trying to make a drawing app inside a bootstrap modal.
So far I have achieved this jsfiddle
Here's my code
var canvasDiv = document.getElementById('canvasDiv');
canvas = document.createElement('canvas');
canvas.setAttribute('width', 570);
canvas.setAttribute('height', 300);
canvas.setAttribute('id', 'canvas');
canvasDiv.appendChild(canvas);
if(typeof G_vmlCanvasManager != 'undefined') {
canvas = G_vmlCanvasManager.initElement(canvas);
}
context = canvas.getContext("2d");
$('#canvas').mousedown(function(e){
var mouseX = e.pageX - this.offsetLeft;
var mouseY = e.pageY - this.offsetTop;
paint = true;
addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop);
redraw();
});
$('#canvas').mousemove(function(e){
if(paint){
addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop, true);
redraw();
}
});
$('#canvas').mouseup(function(e){
paint = false;
});
$('#canvas').mouseleave(function(e){
paint = false;
});
var clickX = new Array();
var clickY = new Array();
var clickDrag = new Array();
var paint;
function addClick(x, y, dragging)
{
clickX.push(x);
clickY.push(y);
clickDrag.push(dragging);
}
function redraw(){
context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears the canvas
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clickX.length; i++) {
context.beginPath();
if(clickDrag[i] && i){
context.moveTo(clickX[i-1], clickY[i-1]);
}else{
context.moveTo(clickX[i]-1, clickY[i]);
}
context.lineTo(clickX[i], clickY[i]);
context.closePath();
context.stroke();
}
}
But when the mouse is clicked, the drawing is being made way off from where the mouse pointer is. Check the fiddle to get an understanding of what I mean.
Also I would like to know how to make the canvas take the height and width of the modal and not pass in static width and height like this canvas.setAttribute('width', 570);

1.offsetleft is relative to parent element https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/offsetLeft , so you need $.offset
2.height and width is according to parent after it shows
result see https://jsfiddle.net/hj898aqb/1/

Conflict with two functions in javascript for canvas drawing

There are two different functions are used to draw the free drawing and line drawing on a canvas. But when a function is called other function not working properly. If the line drawing function called first, and when we press the button to draw free it also draws the line. In the opposite case the continuous line get drawn.The two function are given below.
For free drawing
function free(){
var canvas=document.getElementById('canvas');
var radius=10;
var dragging1=false;
context.lineWidth=2*radius;
var putPoint=function(e) {
if(dragging1){
context.lineTo(e.clientX,e.clientY);
context.stroke();
context.beginPath();
context.arc(e.clientX,e.clientY,radius,0,Math.PI*2);
context.fill();
context.beginPath();
context.moveTo(e.clientX,e.clientY);
}//end of if
}
var engage = function(e) {
dragging1=true;
putPoint(e);
}
var disengage = function() {
dragging1=false;
context.beginPath();
}
canvas.addEventListener('mousedown',engage);
canvas.addEventListener('mousemove',putPoint);
canvas.addEventListener('mouseup',disengage);
}
For Line Drwawing
function line(){
var canvas,
context,
dragging = false,
dragStartLocation,
snapshot;
function getCanvasCoordinates(event) {
var x = event.clientX - canvas.getBoundingClientRect().left,
y = event.clientY - canvas.getBoundingClientRect().top;
return {x: x, y: y};
}
function takeSnapshot() {
snapshot = context.getImageData(0, 0, canvas.width, canvas.height);
}
function restoreSnapshot() {
context.putImageData(snapshot, 0, 0);
}
function drawLine(position) {
context.beginPath();
context.moveTo(dragStartLocation.x, dragStartLocation.y);
context.lineTo(position.x, position.y);
context.stroke();
}
function dragStart(event) {
dragging = true;
dragStartLocation = getCanvasCoordinates(event);
takeSnapshot();
}
function drag(event) {
var position;
if (dragging === true) {
restoreSnapshot();
position = getCanvasCoordinates(event);
drawLine(position);
}
}
function dragStop(event) {
dragging = false;
restoreSnapshot();
var position = getCanvasCoordinates(event);
drawLine(position);
}
function init() {
canvas = document.getElementById("canvas");
context = canvas.getContext('2d');
context.strokeStyle = 'purple';
context.lineWidth = 6;
context.lineCap = 'round';
canvas.addEventListener('mousedown', dragStart, false);
canvas.addEventListener('mousemove', drag, false);
canvas.addEventListener('mouseup', dragStop, false);
}
init()
}
How can i solve this? Iam stuck at this point.

In this case please create two functions that removes the event listeners in the other function. That means create to function
function removeLineListeners(){
canvas.removeEventListener('mousedown', dragStart);
canvas.removeEventListener('mousemove', drag);
canvas.removeEventListener('mouseup', dragStop);
}
and
function removeFreeListeners(){
canvas.removeEventListener('mousedown',engage,false);
canvas.removeEventListener('mousemove',putPoint,false);
canvas.removeEventListener('mouseup',disengage,false);
}
So when when add removeLineListeners() to the starting of the free and
removeFreeListeners() to the strting of Line function. This worked for me

Resize and move rectangles drawn on canvas

I am allowing the user to draw rectangles on an image. At the same time , the user should be able to resize or move any of the rectangles at any point of time.
With some help, i have been able to draw the rectangles but i am unable to come up with resizing and moving part of it.
The rectangles that are being drawn do not overlap one another and the same has to be validated while resizing and moving too.
I am using javascript and jquery.
This is a demo of what i have done so far :
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var canvasOffset = $("#canvas").offset();
var offsetX = canvasOffset.left;
var offsetY = canvasOffset.top;
var startX;
var startY;
var isDown = false;
ctx.strokeStyle = "lightgray";
ctx.lineWidth = 3;
function handleMouseDown(e) {
mouseX = parseInt(e.clientX - offsetX);
mouseY = parseInt(e.clientY - offsetY);
// Put your mousedown stuff here
startX = mouseX;
startY = mouseY;
isDown = true;
}
function handleMouseUp(e) {
mouseX = parseInt(e.clientX - offsetX);
mouseY = parseInt(e.clientY - offsetY);
$("#uplog").html("Up: " + mouseX + " / " + mouseY);
// Put your mouseup stuff here
isDown = false;
}
function handleMouseMove(e) {
mouseX = parseInt(e.clientX - offsetX);
mouseY = parseInt(e.clientY - offsetY);
// Put your mousemove stuff here
if (!isDown) {
return;
}
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawRectangle(mouseX, mouseY);
}
function drawRectangle(mouseX, mouseY) {
var width = mouseX - startX;
var height = mouseY - startY;
ctx.beginPath();
ctx.rect(startX, startY, width, height);
ctx.stroke();
}
$("#canvas").mousedown(function (e) {
handleMouseDown(e);
});
$("#canvas").mousemove(function (e) {
handleMouseMove(e);
});
$("#canvas").mouseup(function (e) {
handleMouseUp(e);
});
as i am running short of time and i am not able to figure out how this can be done.

AFAK, HTML canvas element is simply an array of pixels.
Then drawing/moving/resizing rectangles is, simply again, to keep redrawing canvas.
So first, drawn objects need to be stored (maybe in array).
Second, corresponding mouse events are necessary.
Last, canvas redrawing is required.
Like:
var boxes = [];
var tmpBox = null;
document.getElementById("canvas").onmousedown = function(e) {...};
document.getElementById("canvas").onmouseup = function(e) {...};
document.getElementById("canvas").onmouseout = function(e) {...};
document.getElementById("canvas").onmousemove = function(e) {...};
Here is JSFiddle for demo: https://jsfiddle.net/wiany11/p7hxjmsj/14/

These 2 tutorials explain what you want:
http://simonsarris.com/blog/510-making-html5-canvas-useful
http://simonsarris.com/blog/225-canvas-selecting-resizing-shape
In short you should store the borders of the rectangles yourself and detect when the user clicks in the rectangle or on the border.
First you create an array to store your rectangles in
var rectangles = [];
Then you make a method to call every time you want to draw all your rectangles
function drawRectangles() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for(var i = 0; i < rectangles.length; i++) {
var rect = rectangles[i];
ctx.beginPath();
ctx.rect(rect.startX, rect.startY, rect.endX, rect.endY);
ctx.stroke();
ctx.closePath();
}
}
In your mouseUp you then push the rectangles you have created to the array
function handleMouseUp() {
...
// store the rectangle as an object in your array
var rectangle = {startX: startX, endX: mouseX, startY: startY, endY: mouseY};
rectangles.push(rectangle);
drawRectangles();
}
In your other handlers you can then detect if you click in a rectangle of when your mouse will move in one

You can't just draw objects onto the canvas if you want to move them. You need to create instances of your shape objects and manage those (hit-testing and rendering as required). It is not very complex, but requires a lot more code than you have so far.
Try this tutorial: http://simonsarris.com/blog/510-making-html5-canvas-useful

how can I put multiple objects on the same canvas?

i'm creating a web page where you dynamically draw multiple rectangles. I can draw the single object, but once I tried to draw another one, the previous one is gone away. I tried to save the state using save() and restore(), and it seems that I can't put it here. Isn't it logical that save method is put in the mouseup and restore method is called in the mousedown event? Any help or advice will be appreciated.
const canvas = document.getElementById("circle"),
ctx = canvas.getContext("2d"),
circle = {},
drag = false,
circleMade = false,
mouseMoved = false;
function draw() {
ctx.beginPath();
ctx.arc(circle.X, circle.Y, circle.radius, 0, 2.0 * Math.PI);
ctx.stroke();
}
function mouseDown(e) {
ctx.restore();
circle.startX = e.pageX - this.offsetLeft;
circle.startY = e.pageY - this.offsetTop;
circle.X = circle.startX;
circle.Y = circle.startY;
if (!circleMade) {
circle.radius = 0;
}
drag = true;
}
function mouseUp() {
drag = false;
circleMade = true;
if (!mouseMoved) {
circle = {};
circleMade = false;
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
mouseMoved = false;
ctx.save();
}
function mouseMove(e) {
if (drag) {
mouseMoved = true;
circle.X = e.pageX - this.offsetLeft;
circle.Y = e.pageY - this.offsetTop;
if (!circleMade) {
circle.radius = Math.sqrt(Math.pow((circle.X - circle.startX), 2) + Math.pow((circle.Y - circle.startY), 2));
}
ctx.clearRect(0, 0, canvas.width, canvas.height);
draw();
}
}
function init() {
canvas.addEventListener('mousedown', mouseDown, false);
canvas.addEventListener('mouseup', mouseUp, false);
canvas.addEventListener('mousemove', mouseMove, false);
}
init();

you need to save the information about what you are drawing in a separate object, every time you make a draw to the canvas you will wipe and redraw the new object.
so when you clearRect and then draw you are clearing and then drawing a fresh one but the old ones are being left behind. A good example:
var SavedCircles = [];
var circleInfo = function()
{
this.x = 0;
this.y = 0;
this.startX = 0;
this.startY = 0;
this.radius = 0;
}
circle = {};
function draw()
{
for(var x=0;x<SavedCircles.length;x++)
{
ctx.beginPath();
ctx.arc(SavedCircles[x].X, SavedCircles[x].Y, SavedCircles[x].radius, 0, 2.0 * Math.PI);
ctx.stroke();
}
}
function mouseDown()
{
circle = new circleInfo();
}
function mouseUp()
{
SavedCircles.push(circle);
}
function mouseMove()
{
draw();
}
so you can get rid of save and restore, also its much faster to clear a canvas simply by:
canvas.width = canvas.width;
this should help you keep all circles ever drawn. fill in the rest with your code.

Html5-canvas- How to remove space between the point I click and the draw point

please see the image below for better understanding what I mean :
http://8pic.ir/images/c6kzf0n0eu1v81sv3lit.jpg
as you can see, I scrolled down and when I click on canvas to point a position , it gives space between the point I click and the point it draw the line .
this is my code:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw,ch;
var $canvas=$("#canvas");
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var nameimageis =1;
// set some canvas styles
ctx.strokeStyle='black';
// an array to hold user's click-points that define the clipping area
var points=[];
// load the image
var img=new Image();
img.crossOrigin='anonymous';
img.onload=start;
img.src="http://localhost/image/D0D70A02A7_166.18K_{}_6458.JPG";
function start(){
// resize canvas to fit the img
cw=canvas.width=img.width;
ch=canvas.height=img.height;
// draw the image at 25% opacity
drawImage(1);
// listen for mousedown and button clicks
$('#canvas').mousedown(function(e){handleMouseDown(e);});
$('#reset').click(function(){ points.length=0; drawImage(1); });
}
rightclick = function(e) {
e.preventDefault();
if(!e.offsetX) {
e.offsetX = (e.pageX - $(e.target).offset().left);
e.offsetY = (e.pageY - $(e.target).offset().top);
}
var x = e.offsetX, y = e.offsetY;
for (var i = 0; i < points.length; i+=2) {
dis = Math.sqrt(Math.pow(x - points[i], 2) + Math.pow(y - points[i+1], 2));
if ( dis < 6 ) {
points.splice(i, 2);
draw();
record();
return false;
}
}
return false;
};
function handleMouseDown(e){
// tell the browser that we're handling this event
e.preventDefault();
e.stopPropagation();
// calculate mouseX & mouseY
mx=parseInt(e.clientX-offsetX);
my=parseInt(e.clientY-offsetY);
// push the clicked point to the points[] array
points.push({x:mx,y:my});
// show the user an outline of their current clipping path
outlineIt();
// if the user clicked back in the original circle
// then complete the clip
/*if(points.length>1){
var dx=mx-points[0].x;
var dy=my-points[0].y;
if(dx*dx+dy*dy<10*10){
clipIt();
}
}*/
}
// redraw the image at the specified opacity
function drawImage(alpha){
ctx.clearRect(0,0,cw,ch);
ctx.globalAlpha=alpha;
ctx.drawImage(img,0,0);
ctx.globalAlpha=1.00;
}
// show the current potential clipping path
function outlineIt(){
drawImage(1);
ctx.beginPath();
ctx.moveTo(points[0].x,points[0].y);
for(var i=0;i<points.length;i++){
ctx.lineTo(points[i].x,points[i].y);
}
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.arc(points[0].x,points[0].y,10,0,Math.PI*2);
ctx.closePath();
ctx.stroke();
}
How can I remove this space and point the right position every where I clicked?

It's because you are using e.clientY in function handleMouseDown. clientX/Y is relative to the viewport, not the document. Try use e.pageX/Y, which are relative to the document content.
More details in this question.