Develop Reference

Get mouse position on responsive canvas on mousemove [duplicate]

This question already has answers here:
Real mouse position in canvas
(5 answers)
Closed 4 years ago.
I have a responsive canvas with and it draw a square on mousemove, however I cannot target the mouse position of the canvas, however it works if the canvas is not responsive. how can I target the position of the mouse? Thank you in advance.
https://jsfiddle.net/Paul017/yz028mwe/3/
This is the code.
HTML:
<h4>Drag the mouse to create a rectangle</h4>
<canvas id="canvas" width=300 height=300></canvas>
CSS:
body{ background-color: ivory; }
#canvas{border:1px solid red; width:100%}
JS:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.strokeStyle = "rgba(255, 235, 59, 0.5)";
ctx.fillStyle = "red";
ctx.fill();
ctx.lineWidth = 1;
var $canvas = $("#canvas");
var canvasOffset = $canvas.offset();
var offsetX = canvasOffset.left;
var offsetY = canvasOffset.top;
var scrollX = $canvas.scrollLeft();
var scrollY = $canvas.scrollTop();
var isDown = false;
var startX;
var startY;
function handleMouseDown(e) {
e.preventDefault();
e.stopPropagation();
startX = parseInt(e.clientX - offsetX);
startY = parseInt(e.clientY - offsetY);
// set a flag indicating the drag has begun
isDown = true;
}
function handleMouseUp(e) {
e.preventDefault();
e.stopPropagation();
isDown = false;
}
function handleMouseOut(e) {
e.preventDefault();
e.stopPropagation();
isDown = false;
}
function handleMouseMove(e) {
e.preventDefault();
e.stopPropagation();
// if we're not dragging, just return
if (!isDown) {
return;
}
// get the current mouse position
mouseX = parseInt(e.clientX - offsetX);
mouseY = parseInt(e.clientY - offsetY);
ctx.clearRect(0, 0, canvas.width, canvas.height);
var width = mouseX - startX;
var height = mouseY - startY;
ctx.strokeRect(startX, startY, width, height);
}

You can use the selectionStart or selectionEnd property of target method.
You can get target every position with:
e.target.selectionStart
or e.target.selectionEnd
In your code:
function handleMouseMove(e) {
console.log('target event ', e.target);
console.log('selectionStart', e.target.selectionStart);
console.log('selectionEnd', e.target.selectionEnd)
e.preventDefault();
e.stopPropagation();
// if we're not dragging, just return
if (!isDown) {
return;
}
// get the current mouse position
mouseX = parseInt(e.clientX - offsetX);
mouseY = parseInt(e.clientY - offsetY);
ctx.clearRect(0, 0, canvas.width, canvas.height);
var width = mouseX - startX;
var height = mouseY - startY;
ctx.strokeRect(startX, startY, width, height);
}
If the console log show undefined, try to console log you e.target. You will find the selectionStart and selectionEnd method.
Let me know if you need something else.

I have already figured it out by using these mouse positions code to target the x and y location in a responsive canvas
e.offsetX * canvas.width / canvas.clientWidth | 0
e.offsetY * canvas.width / canvas.clientWidth | 0
https://jsfiddle.net/Paul017/yz028mwe/28/

Mouse cursor doesn't match with canvas

I have question: when I'm drawing a line in canvas, it seems the mouse position doesn't match with the canvas position, so whenever I draw, there is some distance between my cursor and the drawing line .. please help me with this problem, here is my code :
$(document).ready(function(){
context = document.getElementById('canvasInAPerfectWorld').getContext("2d");
$('#canvasInAPerfectWorld').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();
});
$('#canvasInAPerfectWorld').mousemove(function(e){
if(paint){
addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop, true);
redraw();
}
});
$('#canvasInAPerfectWorld').mouseup(function(e){
paint = false;
});
$('#canvasInAPerfectWorld').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 clear_canvas(){
//alert('masuk claear');
context.clearRect(0,0,context.canvas.width,context.canvas.height);
}
function redraw(){
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();
}
}

Inside your mouse event handlers, this refers to the window object and your this.offsetLeft is undefined.
You can use getBoundingClientRect to get the bounds of your canvas element:
// get a reference to your canvas element at the start of your app
var canvas=document.getElementById('canvasInAPerfectWorld');
// example mousedown handler
// get the current canvas offsets using getBoundingClientRect
var BB=canvas.getBoundingClientRect();
var offsetX=BB.left;
var offsetY=BB.top;
// calculate the current mouse position relative to the canvas
// using e.client and the offsets calculated above
var mouseX=parseInt(e.clientX-offsetX);
var mouseY=parseInt(e.clientY-offsetY);
If you canvas does not reposition relative to the viewport, you can get the offsets once at the start of your app so they don't need to be recalculated every time inside the mouse handler.

You could follow the solution in markE's answer (also found here).
Or you could do the following if your layout allows
Set canvas element to position relative
Use layerX and layerY to read the mouse position
This approach gives a little simpler code.
Both methods will be affected by padding and border thickness (they need to be subtracted if any is used). If you want border/padding it's better to wrap the canvas in a div and then style the div instead.
Example using relative positioned canvas
var c = document.querySelector("canvas"),
ctx = c.getContext("2d");
ctx.font = "bold 16px sans-serif";
c.onmousemove = function(e) {
var x = e.layerX,
y = e.layerY;
ctx.clearRect(0, 0, 300, 20);
ctx.fillText("x: " + x + ", y: " + y, 10, 16);
};
div {padding:20px}
canvas {background:#eee; position:relative}
<div><div><canvas></canvas></div></div>
Example using getBoundingClientRect()
var c = document.querySelector("canvas"),
ctx = c.getContext("2d");
ctx.font = "bold 16px sans-serif";
c.onmousemove = function(e) {
var rect = this.getBoundingClientRect(),
x = e.clientX - rect.left,
y = e.clientY - rect.top;
ctx.clearRect(0, 0, 300, 20);
ctx.fillText("x: " + x + ", y: " + y, 10, 16);
};
div {padding:20px}
canvas {background:#eee; position:relative}
<div><div><canvas></canvas></div></div>

Drawing circle/ellipse on HTML5 canvas using mouse events

I want something like ellipse option in paint for drawing on my canvas. I have achieved this partially. The problem is I am not able to get radius of circle; currently I have hard coded it to 15. Also I want to draw an ellipse (like in paint) not exact circle.
This is my code for drawing circle on canvas using mouse events. Please help me with code to achieve my above mentioned requirements.
function tool_circle() {
var tool = this;
this.started = false;
this.mousedown = function (ev) {
tool.started = true;
tool.x0 = ev._x;
tool.y0 = ev._y;
};
this.mousemove = function (ev) {
if (!tool.started) {
return;
}
context.fillStyle = 'red';
var distance = Math.sqrt(Math.pow(tool.x0 - ev._x, 2) + Math.pow(tool.y0 - ev._y));
context.beginPath();
context.arc(tool.x0, tool.y0,15, 0, Math.PI * 2, false);
context.stroke();
context.fill();
};
this.mouseup = function (ev) {
if (tool.started) {
tool.mousemove(ev);
tool.started = false;
img_update();
}
};
}

I would something similar as with markE's answer however, using Bezier curve will draw ellipses but it won't give you the exact radius that you probably would need.
For that a function to draw a manual ellipse is needed, and it's rather simple -
This function will take a corner start point and and end point and draw an ellipse exactly within that boundary:
Live demo
function drawEllipse(x1, y1, x2, y2) {
var radiusX = (x2 - x1) * 0.5, /// radius for x based on input
radiusY = (y2 - y1) * 0.5, /// radius for y based on input
centerX = x1 + radiusX, /// calc center
centerY = y1 + radiusY,
step = 0.01, /// resolution of ellipse
a = step, /// counter
pi2 = Math.PI * 2 - step; /// end angle
/// start a new path
ctx.beginPath();
/// set start point at angle 0
ctx.moveTo(centerX + radiusX * Math.cos(0),
centerY + radiusY * Math.sin(0));
/// create the ellipse
for(; a < pi2; a += step) {
ctx.lineTo(centerX + radiusX * Math.cos(a),
centerY + radiusY * Math.sin(a));
}
/// close it and stroke it for demo
ctx.closePath();
ctx.strokeStyle = '#000';
ctx.stroke();
}
The demo marks the rectangle area too to show that the ellipse is exactly within it.
Draw
To handle mouse operation that will let you draw the ellipse you can do:
var canvas = document.getElementById('myCanvas'),
ctx = canvas.getContext('2d'),
w = canvas.width,
h = canvas.height,
x1, /// start points
y1,
isDown = false; /// if mouse button is down
/// handle mouse down
canvas.onmousedown = function(e) {
/// get corrected mouse position and store as first point
var rect = canvas.getBoundingClientRect();
x1 = e.clientX - rect.left;
y1 = e.clientY - rect.top;
isDown = true;
}
/// clear isDown flag to stop drawing
canvas.onmouseup = function() {
isDown = false;
}
/// draw ellipse from start point
canvas.onmousemove = function(e) {
if (!isDown) return;
var rect = canvas.getBoundingClientRect(),
x2 = e.clientX - rect.left,
y2 = e.clientY - rect.top;
/// clear canvas
ctx.clearRect(0, 0, w, h);
/// draw ellipse
drawEllipse(x1, y1, x2, y2);
}
A tip can be to create a top canvas on top of your main canvas and do the drawing itself there. When mouse button is released then transfer the drawing to your main canvas. This way you don't have to redraw everything when drawing a new shape.
Hope this helps!

Here's an example of how to drag-draw an oval.
Demo: http://jsfiddle.net/m1erickson/3SFJy/
Example code using 2 Bezier curves to drag-draw an oval:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; padding:0px;}
#canvas{ border:1px solid blue; }
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var startX;
var startY;
var isDown=false;
function drawOval(x,y){
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.beginPath();
ctx.moveTo(startX, startY + (y-startY)/2);
ctx.bezierCurveTo(startX, startY, x, startY, x, startY + (y-startY)/2);
ctx.bezierCurveTo(x, y, startX, y, startX, startY + (y-startY)/2);
ctx.closePath();
ctx.stroke();
}
function handleMouseDown(e){
e.preventDefault();
e.stopPropagation();
startX=parseInt(e.clientX-offsetX);
startY=parseInt(e.clientY-offsetY);
isDown=true;
}
function handleMouseUp(e){
if(!isDown){ return; }
e.preventDefault();
e.stopPropagation();
isDown=false;
}
function handleMouseOut(e){
if(!isDown){ return; }
e.preventDefault();
e.stopPropagation();
isDown=false;
}
function handleMouseMove(e){
if(!isDown){ return; }
e.preventDefault();
e.stopPropagation();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
drawOval(mouseX,mouseY);
}
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouseout(function(e){handleMouseOut(e);});
}); // end $(function(){});
</script>
</head>
<body>
<h4>Drag to create a circle or oval</h4>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

Here's my way of drawing an ellipse onto a canvas with mouse drag.
It uses radius of 1, but dynamic scaling to get the ellipse effect :)
https://jsfiddle.net/richardcwc/wdf9cocz/
//Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
//Variables
var scribble_canvasx = $(canvas).offset().left;
var scribble_canvasy = $(canvas).offset().top;
var scribble_last_mousex = scribble_last_mousey = 0;
var scribble_mousex = scribble_mousey = 0;
var scribble_mousedown = false;
//Mousedown
$(canvas).on('mousedown', function(e) {
scribble_last_mousex = parseInt(e.clientX-scribble_canvasx);
scribble_last_mousey = parseInt(e.clientY-scribble_canvasy);
scribble_mousedown = true;
});
//Mouseup
$(canvas).on('mouseup', function(e) {
scribble_mousedown = false;
});
//Mousemove
$(canvas).on('mousemove', function(e) {
scribble_mousex = parseInt(e.clientX-scribble_canvasx);
scribble_mousey = parseInt(e.clientY-scribble_canvasy);
if(scribble_mousedown) {
ctx.clearRect(0,0,canvas.width,canvas.height); //clear canvas
//Save
ctx.save();
ctx.beginPath();
//Dynamic scaling
var scalex = 1*((scribble_mousex-scribble_last_mousex)/2);
var scaley = 1*((scribble_mousey-scribble_last_mousey)/2);
ctx.scale(scalex,scaley);
//Create ellipse
var centerx = (scribble_last_mousex/scalex)+1;
var centery = (scribble_last_mousey/scaley)+1;
ctx.arc(centerx, centery, 1, 0, 2*Math.PI);
//Restore and draw
ctx.restore();
ctx.strokeStyle = 'black';
ctx.lineWidth = 5;
ctx.stroke();
}
//Output
$('#output').html('current: '+scribble_mousex+', '+scribble_mousey+'<br/>last: '+scribble_last_mousex+', '+scribble_last_mousey+'<br/>mousedown: '+scribble_mousedown);
});
canvas {
cursor: crosshair;
border: 1px solid #000000;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="canvas" width="800" height="500"></canvas>
<div id="output"></div>

Multi canvas drawing issue

I am building a paint tool application.I am using two canvases. One for loading a background image and one for do the painting. Painting canvas is placed over the other one. I used two canvases because i don't want the eraser tool to take effect on the image. On my code y position drawn by the application is not always accurate. In most cases the line is drawn higher than the actual drawn path.
var baseCanvas,baseContext,canvasObj,context;
var lastX,lastY,mouseX,mouseY;
var isMouseDown = false;
var mode = "pen";
$(window).load(function()
{
baseCanvas = document.getElementById("imageCanvas");
baseContext = baseCanvas.getContext("2d");
baseContext.strokeStyle = 'Black';
baseContext.fillStyle = "skyBlue";
baseContext.lineWidth = 5;
baseContext.fillRect(0, 0, baseCanvas.width, baseCanvas.height);
canvasObj = document.getElementById("drawingCanvas");
context = canvasObj.getContext("2d");
context.strokeStyle = 'Black';
context.lineCap = "round";
context.lineJoin = "round";
context.lineWidth = 2;
function handleMouseDown(e) {
mouseX = parseInt(e.clientX - $('#drawingCanvas').offset().left);
mouseY = parseInt(e.clientY - $('#drawingCanvas').offset().top);
lastX = mouseX;
lastY = mouseY;
isMouseDown = true;
}
function handleMouseUp(e) {
mouseX = parseInt(e.clientX - $('#drawingCanvas').offset().left);
mouseY = parseInt(e.clientY - $('#drawingCanvas').offset().top);
isMouseDown = false;
}
function handleMouseOut(e) {
mouseX = parseInt(e.clientX - $('#drawingCanvas').offset().left);
mouseY = parseInt(e.clientY - $('#drawingCanvas').offset().top);
isMouseDown = false;
}
function handleMouseMove(e) {
mouseX = parseInt(e.clientX - $('#drawingCanvas').offset().left);
mouseY = parseInt(e.clientY - $('#drawingCanvas').offset().top);
if (isMouseDown) {
context.beginPath();
if (mode == 'pen') {
context.globalCompositeOperation = "source-over";
context.moveTo(lastX, lastY);
context.lineTo(mouseX, mouseY);
context.stroke();
} else {
context.globalCompositeOperation = "destination-out";
context.arc(lastX, lastY, 5, 0, Math.PI * 2, false);
context.fill();
}
lastX = mouseX;
lastY = mouseY;
}
}
$(document).on('mousedown',$("#drawingCanvas"),function (e) {
handleMouseDown(e);
});
$(document).on('mousemove',$("#drawingCanvas"),function (e) {
handleMouseMove(e);
});
$(document).on('mouseup',$("#drawingCanvas"),function (e) {
handleMouseUp(e);
});
$(document).on('mouseout',$("#drawingCanvas"),function (e) {
handleMouseOut(e);
});
});
function setCanvas(imageFile)
{
var base_image = new Image();
base_image.src = window.URL.createObjectURL(imageFile[0]);
baseContext.save();
baseContext.clearRect(0, 0, baseCanvas.width, baseCanvas.height);
baseContext.beginPath();
base_image.onload = function()
{
baseContext.drawImage(base_image,0,0, $('#imageCanvas').width(), $('#imageCanvas').height());
baseContext.restore();
}
}

If you scroll the browser window, you need to adjust for that scrolling.
Here's how:
var scrollAdjustment=$("html,body").scrollTop();
mouseY+=scrollAdjustment;
And if you scroll horizontally, you would need to adjust for horizontal scrolling too.
BTW, since the canvas offset doesn't change, you could pre-calculate the canvas offsets one time instead of calculating it each time in your event handlers.
In your setup up top:
var canvasOffset=$("#drawingCanvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
And in your event handlers:
var scrollAdjustment=$("html,body").scrollTop();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY+scrollAdjustment);

Provided you are using the clientX, clientY properties of your mouse events, and that you hooked the events on the window, you should getBoundingClientRect on your canvas to know its top and left position, then substract them.
https://developer.mozilla.org/en-US/docs/Web/API/element.getBoundingClientRect
Rq : You might think also about hooking the events on the canvas.

Drawing a rectangle on Canvas

I am trying to create a simple canvas program where the user can consistently create new shapes. This one is just a basic rectangle creator (I am hoping to expand it more to circles, lines, and maybe even other stuff). Right now though I have created something that is working in a really weird way.
<html>
<head>
<meta chartset="utf-8">
<title>Dragging a square</title>
<script type="text/javascript">
var canvas, context, startX, endX, startY, endY;
var mouseIsDown = 0;
function init() {
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
canvas.addEventListener("mousedown", mouseDown, false);
canvas.addEventListener("mousemove", mouseXY, false);
document.body.addEventListener("mouseup", mouseUp, false);
}
function mouseUp() {
mouseIsDown = 0;
//mouseXY();
}
function mouseDown() {
mouseIsDown = 1;
startX = event.clientX;
startY = event.clientY;
mouseXY();
}
function mouseXY(eve) {
if (!eve) {
var eve = event;
}
endX = event.pageX - canvas.offsetLeft;
endY = event.pageY - canvas.offsetTop;
drawSquare();
}
function drawSquare() {
// creating a square
var width = Math.abs(startX - endX);
var height = Math.abs(startY - endY);
context.beginPath();
context.rect(startX, startY, width, height);
context.fillStyle = "yellow";
context.fill();
context.lineWidth = 7;
context.strokeStyle = 'black';
context.stroke();
}
</script>
</head>
<body onload="init()">
<canvas id="canvas" width="400" height="400" style="border: 1px solid black; cursor: pointer;"></canvas>
</body>
</html>
Sorry about the slightly weird formatting when I copy and pasted my code. I think the problem is my mouseXY function. What I want is the user to click somewhere on the canvas a drag the mouse to create a rectangle, when the user lets go that is the end of that operation and they can create a whole new rectangle right after. At this point the program kind of just lets me click and create a new rectangle but if I let go of the mouse button it doesn't stop, in fact I have to click again to make it stop which then creates a new rectangle. I am still very new to this and I am having a lot of trouble with this, I will continue to work on this and if I figure it out I will let the site know. Thank you and have a great day!
Well I got this to work (thanks to #Ken) but now I am trying to solve a new problem. I want to be able to put multiple rectangles on the canvas. I created a function that represents the Rectangle and then created a draw function within the rectangle function to draw out a rectangle. I created a new function called addShape() that ideally creates the rectangle object and pushes into an array called square and drawShapes() that is supposed to erase everything on the canvas and redraws everything. Here is what I have so far:
<html>
<head>
<meta chartset="utf-8">
<title>Dragging a square</title>
<script type="text/javascript">
function Rectangle(canvas, x, y, width, height,color) {
//this.context = canvas.getContext("2d");
this.x = x;
this.y = y;
this.width = width;
this.height = height;
this.color = color;
this.draw = function() {
this.context.globalAlpha = 0.85;
this.context.beginPath();
this.context.rect(this.x, this.y, this.width, this.height);
this.context.fillStyle = this.color;
this.context.strokeStyle = "black";
this.context.lineWidth = 1;
this.context.fill();
this.context.stroke();
};
};
// hold the canvas and context variable, as well as the
// starting point of X and Y and the end ones
var canvas, context, startX, endX, startY, endY;
var mouseIsDown = 0;
// An array that holds all the squares
var squares = [];
window.onload = function() {
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
canvas.addEventListener("mousedown", mouseDown, false);
canvas.addEventListener("mousemove", mouseXY, false);
canvas.addEventListener("mouseup", mouseUp, false);
}
function mouseUp(eve) {
if (mouseIsDown !== 0) {
mouseIsDown = 0;
var pos = getMousePos(canvas, eve);
endX = pos.x;
endY = pos.y;
//Square(); //update on mouse-up
addShape(); // Update on mouse-up
}
}
function mouseDown(eve) {
mouseIsDown = 1;
var pos = getMousePos(canvas, eve);
startX = endX = pos.x;
startY = endY = pos.y;
// Square(); //update
addShape();
}
function mouseXY(eve) {
if (mouseIsDown !== 0) {
var pos = getMousePos(canvas, eve);
endX = pos.x;
endY = pos.y;
//Square();
addShape();
}
}
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
function addShape() {
var w = endX - startX;
var h = endY - startY;
var offsetX = (w < 0) ? w : 0;
var offsetY = (h < 0) ? h : 0;
var width = Math.abs(w);
var height = Math.abs(h);
var s = new Rectangle(startX + offsetX, startY + offsetY, width, height, "yellow");
squares.push(s);
// Update the display
drawShapes();
}
function drawShapes() {
context.clearRect(0,0,canvas.width,canvas.height);
for (var i = 0; i < squares.length; i++) {
var shape = squares[i];
shape.draw();
};
}
function clearCanvas() {
squares = [];
drawShapes();
}
</script>
</head>
<body onload="addShape()">
<canvas id="canvas" width="400" height="400" style="border: 1px solid black; cursor: pointer;"></canvas><br>
<button onclick="clearCanvas()">Clear Canvas</button>
</body>
</html>
I am pretty sure I broke the original code... thank you for any help!

You need to modify a couple of things in the code: (edit: there are many issues with this code. I went through some of them inline here, but haven't tested. If you put it in a fiddle it's easier for us to check)..
Fiddle
When mouse down occur initialize both start and end points. Call a common draw function that is not dependent on the event itself:
function mouseDown(eve) {
mouseIsDown = 1;
var pos = getMousePos(canvas, eve);
startX = endX = pos.x;
startY = endY = pos.y;
drawSquare(); //update
}
At mouse up, only register if isMouseDown is true, else this function will handle all incoming up-events (as you have attatched it to document, which is correct - window could have been used too):
function mouseUp(eve) {
if (mouseIsDown !== 0) {
mouseIsDown = 0;
var pos = getMousePos(canvas, eve);
endX = pos.x;
endY = pos.y;
drawSquare(); //update on mouse-up
}
}
Only draw if mouseisdown is true:
function mouseXY(eve) {
if (mouseIsDown !== 0) {
var pos = getMousePos(canvas, eve);
endX = pos.x;
endY = pos.y;
drawSquare();
}
}
In addition you will need to clear the previous area of the rectangle before drawing a new or else it won't show when you draw a bigger rectangle and then move the mouse back to draw a smaller one.
For simplicity you can do:
function drawSquare() {
// creating a square
var width = Math.abs(startX - endX);
var height = Math.abs(startY - endY);
context.clearRect(0, 0, context.width, context.height);
//or use fillRect if you use a bg color
context.beginPath();
context.rect(startX, startY, width, height);
context.fillStyle = "yellow";
context.fill();
context.lineWidth = 7;
context.strokeStyle = 'black';
context.stroke();
}
Use this for mouse position:
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}