Use something like Node.appendChild( child ) for adding it to the DOM: var canv = document.createElement(‘canvas’); canv.id = ‘someId’; document.body.appendChild(canv); // adds the canvas to the body element document.getElementById(‘someBox’).appendChild(canv); // adds the canvas to #someBox Or you can use element.innerHTML: document.body.innerHTML += ‘<canvas id=”someId”></canvas>’; // the += means we add this to the inner HTML … Read more
Projects with a large amount of data may favor canvas. SVG approaches typically create a DOM node per point (unless you make paths), which can lead to: An explosion in the size of your DOM tree Performance problems Using a path, you can get around this problem, but then you lose interactivity. Say you’re building … Read more
From the documentation, these are the parameters for drawImage: drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh); So, to crop the outer 10 pixels from the source image (Assuming it’s 100 * 50), and then to scale that up to 160*60: ctx.drawImage(image, 10, 10, // Start at 10 pixels from the left and the … Read more
Do not use new Date() This API has several flaws and is only useful for getting the current date + time. Not for measuring timespans. The Date-API uses the operating system’s internal clock, which is constantly updated and synchronized with NTP time servers. This means, that the speed / frequency of this clock is sometimes … Read more
you have to set the color for the text. Something like this: const canvasObj = document.getElementById(‘canvas’) const context = canvasObj.getContext(‘2d’) context.font = “bold 24px verdana, sans-serif “; var welcomeMessage = “Welcome to the store!”; context.textAlign = “start”; context.textBaseline = “bottom”; context.fillStyle = “#ff0000”; //<======= here context.fillText(welcomeMessage, 10, 50); context.font = “bold 14px verdana, sans-serif”; var … Read more
I would suggest Smoothie Charts. It’s very simple to use, easily and widely configurable, and does a great job of streaming real time data. There’s a builder that lets you explore the options and generate code. Disclaimer: I am a contributor to the library.
The second argument of the function is the quality. It ranges from 0.0 to 1.0 canvas.toDataURL(type,quality); Here you have extended information And I don’t think it’s possible to know the quality of the image once is converted. As you can see on this feedle the only information you get when printing the value on the … Read more
From a JQuery bug tracker page – a nice polyfill is this: var offX = (e.offsetX || e.pageX – $(e.target).offset().left); .. where e is the event returned from a jquery event. Obviously, only if you’ve got Jquery already on your project, otherwise will have to do the offset() stuff manually.
There is no built-in method to change background color, but you can use CSS. JSFiddle. ctx.style.backgroundColor=”rgba(255,0,0,255)”; EDIT If you want to fill exact area of chart and no whole div, you can write your own chart.js plugin. Try it on JSFiddle. Chart.pluginService.register({ beforeDraw: function (chart, easing) { if (chart.config.options.chartArea && chart.config.options.chartArea.backgroundColor) { var ctx = … Read more
ctx.canvas should return the canvas DOM node, from which you can get height and width. I tried it with https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Basic_usage Firefox was able to return ctx.canvas, as well as ctx.canvas.width and ctx.canvas.height. Also confirmed in Chrome.