Draw a rectangle on a image inside a canvas using mousemove event in javascript
You probably need to first clear the entire canvas using clearRect
, then draw your imageObj
immediately and finally, draw the stroke. All of this happening inside the mouseMove
function so it basically keeps drawing these elements on a continuous basis.
Try this snippet below:
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var rect = {};
var drag = false;
var imageObj = null;
function init() {
imageObj = new Image();
imageObj.onload = function () { ctx.drawImage(imageObj, 0, 0); };
imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
canvas.addEventListener('mousedown', mouseDown, false);
canvas.addEventListener('mouseup', mouseUp, false);
canvas.addEventListener('mousemove', mouseMove, false);
}
function mouseDown(e) {
rect.startX = e.pageX - this.offsetLeft;
rect.startY = e.pageY - this.offsetTop;
drag = true;
}
function mouseUp() { drag = false; }
function mouseMove(e) {
if (drag) {
ctx.clearRect(0, 0, 500, 500);
ctx.drawImage(imageObj, 0, 0);
rect.w = (e.pageX - this.offsetLeft) - rect.startX;
rect.h = (e.pageY - this.offsetTop) - rect.startY;
ctx.strokeStyle = 'red';
ctx.strokeRect(rect.startX, rect.startY, rect.w, rect.h);
}
}
//
init();
<canvas id="canvas" width="500" height="500"></canvas>
Hope this is what you were looking for and helps you in some way.
P.S. I have intentionally applied the red
colour on the stroke. You can remove it of course.
Gajini
Updated on June 07, 2022Comments
-
Gajini almost 2 years
I am trying to draw a rectangle on an image that is inside canvas using mousemove event . But i am getting rectangle on the image with color filled in the rectangle because of clearRect . can anyone figure me out . how to draw a rectangle with just a border on the image . Below is the code that i followed to achieve it .
var canvas = document.getElementById('canvas'), ctx = canvas.getContext('2d'), rect = {}, drag = false; function init() { var imageObj = new Image(); imageObj.onload = function() { ctx.drawImage(imageObj, 0, 0); }; imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg'; canvas.addEventListener('mousedown', mouseDown, false); canvas.addEventListener('mouseup', mouseUp, false); canvas.addEventListener('mousemove', mouseMove, false); } function mouseDown(e) { rect.startX = e.pageX - this.offsetLeft; rect.startY = e.pageY - this.offsetTop; drag = true; } function mouseUp() { drag = false; } function mouseMove(e) { if (drag) { rect.w = (e.pageX - this.offsetLeft) - rect.startX; rect.h = (e.pageY - this.offsetTop) - rect.startY ; ctx.clearRect(rect.startX, rect.startY,rect.w,rect.h); draw(); } } function draw() { ctx.clearRect(rect.startX, rect.startY, rect.w, rect.h); ctx.strokeRect(rect.startX, rect.startY, rect.w, rect.h); }
<head> <meta charset="utf-8" /> <title>Draw a rectangle!</title> </head> <body onload="init();"> <canvas id="canvas" width="500" height="500"></canvas> </body>