---
title: Drag image on HTML Canvas with JavaScript
slug: drag-image-on-html-canvas-with-javascript
published_at: 2021-04-02 17:00:02 +0000
updated_at: 2026-03-04 20:14:19 +0000
summary:
description: Learn how to drag image on HTML Canvas with JavaScript. We're building on the last episode where we used the bitmoji API to add stickers to a thumbnail canvas. In this episode, we listen for mouse events on the canvas and redraw based on where the sticker is dragged. Code: https://github.com/cjavdev/video_automation Twitter: https://twitter.com/cjav_dev Feedback: https://forms.gle/Q31hhjJGsMrvY4mL6 It turns out there's a really excellent tool called TubeBuddy that already exists and does most of what I was planning to build. I've started using TubeBuddy in the past few months and really like it. If you use this link to buy a license, I'll get a small cut for being an affiliate: https://www.tubebuddy.com/cjavdev.
tags: [Drag image on HTML Canvas with JavaScript, Drag image on HTML Canvas, drag image on canvas, html canvas, javascript, HTML Canvas with JavaScript, canvas mouse events]
views: 14337
author: CJ Avilla
url: https://www.cjav.dev/videos/drag-image-on-html-canvas-with-javascript
youtube_url: https://www.youtube.com/watch?v=6dpxrBTESvQ
youtube_id: 6dpxrBTESvQ
embed_url: https://www.youtube.com/embed/6dpxrBTESvQ
thumbnail_url: https://i.ytimg.com/vi/6dpxrBTESvQ/hqdefault.jpg
type: video
---
# Drag image on HTML Canvas with JavaScript
*Published: April 02, 2021*
*Views: 14337*
## Watch
[Watch on YouTube](https://www.youtube.com/watch?v=6dpxrBTESvQ)
[](https://www.youtube.com/watch?v=6dpxrBTESvQ)
## Description
Learn how to drag image on HTML Canvas with JavaScript. We're building on the last episode where we used the bitmoji API to add stickers to a thumbnail canvas. In this episode, we listen for mouse events on the canvas and redraw based on where the sticker is dragged.
Code: https://github.com/cjavdev/video_automation
Twitter: https://twitter.com/cjav_dev
Feedback: https://forms.gle/Q31hhjJGsMrvY4mL6
It turns out there's a really excellent tool called TubeBuddy that already exists and does most of what I was planning to build. I've started using TubeBuddy in the past few months and really like it. If you use this link to buy a license, I'll get a small cut for being an affiliate: https://www.tubebuddy.com/cjavdev.
## Transcript
hey what's up friends in this episode we're going to talk about how to move an image around an html canvas so that we can continue working on our thumbnail builder or generator for uh working with youtube so in the previous episode we talked all about how to get this bitmoji sticker picker set up if you haven't seen that episode it's pretty fun um and it's actually surprisingly simple when you click on a sticker here we are rendering it into our svg page it's just this is kind of funny because um the more stickers we click it's just adding new ones it's not actually clearing them out but what i wanted to do in this in this episode is like show how we can maybe click on a photo and then drag it so that we can place it where we want it again with the idea that like we're going to make a tool so that we can easily generate thumbnails that are synced to youtube so by default we don't want it always in this top right corner and in fact we want it probably down over here in this kit in the case of this style of thumbnail so let's go implement that now so if you recall at the very top this is our bitmoji sticker picker thing and then we have a generate png button so when we click on generate png that actually generates our ultimate png file that can be uploaded directly to the youtube api with the um yeah with with the youtube data v3 api which we covered in a previous episode so if you want to check that out we have also got content about how to upload thumbnails to youtube using ruby on rails um okay so what i wanted to do today was just talk about how this works so we've got our snap kit that's initialized and we have when the sticker pick callback runs we are creating a new image we are setting that image's source tag equal to the url the bitmoji url for that i needed to add this cross origin equal anonymous so that when we rendered it into the html canvas context it did not consider it tainted because other if you don't pass this cross origin then it expects that images are directly um from the same domain so by saying cross-origin anonymous and thankfully bitmoji does allow cores requests or whatever so we're able to then convert this to a png so what we want to do now is like instead of sticking this thing at zero zero just in the top left corner let's try to make it right in the middle um so i've got the sticker image i think we also want like where where the current x and y of the image are so we'll say like current x and current y and initially let's just set these to the center of the canvas so canvas dot width divided by 2 and canvas dot height divided by 2. and let's see if that will drop it in the middle can or let's see current x and current y let's see all right so now if we add a whoops we have to go back to the flow here the oauth flow i think it the the sessions are pretty short um okay so then if we click on the that it ends up being sort of centered but i think it's because the top left corner like this is a square sticker picture right the top left corner i believe is maybe centered in the middle of the of the canvas but the image is not so i think we need to account for like the height and width of the image so we're let's just say that we want to put the image at current x minus sticker image dot width divided by 2 and the current y is going to be minus sticker image dot height divided by 2. let's see if that gets us a little closer to the middle and then we say hey hey hey all right so that's sort of smack in the middle that looks pretty good so the next thing that we want to do is use some of the functions that are available on the canvas for mouse events so let's register some mouse events on the can on the canvas so we're gonna have canvas dot on mouse down that'll be a function and then we'll have canvas dot on mouse out i think is another function and canvas on mouse up um on mouse up let's just see if these work also so we'll say like console.log mouse down and then we'll say like e dot layer x and e dot layer y i i think we want to use the layers x and y so it's relative to the i believe that's relative to the canvas i'm not actually sure up and then out if you know uh what the difference is between like the mouse events layer x page x and uh there's a whole bunch of different like x and y coordinates that you get from a mouse event i would love to know so leave a comment down in the description if you have um if you have some deep knowledge about how mouse events work okay so we are we are rendering these right so like uh if we mouse out then it you'll see in the console down here right that the mouse out event is happening and if we mouse down we see mouse down we can drag around and then mouse up that happens and then we have mouse out cool so what i want to do is i want to i want to make a new a new variable called draggable and we'll set it to false initially and then we we need to like detect if uh the click was on the image or just like even if it was just close to it and then if for if we mouse up or if we mouse out we want to set draggable back to false okay so when we're detecting if the click was on the image how is this going to work so we want to see if the images click so this layer x in layer y was on the image so we kind of need to see like was it inside of the bounds so if e dot layer x is less than or equal to something and e dot layer x was greater than or equal to something then we'll say draggable is equal to true and we'll just console.log like clicked image otherwise we'll say else like console.log didn't click didn't click the image and uh so what is this actually going to look like so um if if where we click on the page is less than um what is going to be the far right bound is going to be the right edge of the sticker and the right edge of the sticker is going to be like current x plus sticker image dot width over 2 right and then so that's going to be the far right edge of the image the far left edge of the image is going to be current x minus sticker image dot width divided by two because that that'll kind of like give us the two edges the two edges of the image right so let's see if this works so if we pick our image here and let's just say good vibes and then if we click on it it says clicked image that's pretty cool if we click over here didn't click image this is going to say clicked image if we click above or below because we're not looking at y bounds we're just looking at x bounds but the same now we can like kind of copy our logic here and then just say instead of x we can say um uh layer x to layer y and in fact like uh we'll just change x for y in this in this row here um all right so and then instead of width this needs to be height all right so let's see if that worked so we need to add an image to the page again or an image back to our svg all right didn't click the image so i'm looking down here in the console for um for this console.logs so clicked the image didn't click the image clicked the image okay this is great so the next step is that like now we know whether or not um we're draggable so we can just check this like draggable variable right um let me just clean this up a little bit too so we've got our stuff that makes it a little bit visible so uh okay so um we're detecting if the image was clicked and if so we're setting it to drag we're setting draggable to true and if it's draggable then what we want to do is like move to a new current x and current y i believe right so how is this going to work so i think then also like we need to redraw the image at the new current x and the new current y um so i think we might need to say mouse move on mouse move so canvas dot on mouse move is another event and if we're moving around so if draggable so if we're moving and and we're draggable meaning that we clicked down on the image then we need to update current x and current y so current x should be equal to like e dot layer x and current y should be equal to e dot layer y i think all right let's see let's see if this works so we want uh actually how is this how is this going to work so then now that we have the new current x and current y every single like on some interval we need to like re-render the image right we need to like redraw the image so instead of just drawing it once on load here i think i want to do this like um in an interval so set interval so this runs several times and then we'll just say like do this every 200 milliseconds or something and because we're using current x and current y i think this should work just fine so we're gonna um every 200 milliseconds we will redraw the image so let's refresh this so we'll pick a sticker and drop that smack in the middle oh look at that okay so i've clicked and i'm dragging it around and then if i let go i can click and drag it again from the same spot okay this is super cool but do you notice a problem there's a lot of that's a lot of i love use okay so the problem is that like it's not as we're moving the image around it's leaving the old images that were printed but it's not removing them um so it's also probably like this draw image thing is never like clearing it out it's just like constantly drawing new ones uh probably way too much so that's a little bit messy um all right so let's see what we what we actually need to do so in addition to drawing the image we kind of need to like um reset the canvas and resetting the canvas really has to do with this initial load so um drawing this image here so const reset canvas is uh is a function that we will just we'll just do this thing so we'll just call draw image from from the svg so this is the old like this is basically like the background um so we'll let's just try this out so let's see what happens so if we add a an image here oh my gosh look at that so cool all right so then after we've got it in the right position if we say generate png boom all right cool so that is how you move an image around on on a canvas so it required a couple different things this is just like a quick recap we added a new variable called draggable which we set to true only if we detected a mouse down event that was on the image which we figured out based on where we placed the image initially and based on the size of the image and then the current x and current y is sort of like the constantly moving center of the image and then on mouse move we updated that x and y and then on mouse up or mouse out then we just like set it to draggable false so in fact like if we if we um if we drag the image and go out of the frame notice that it just does the mouse out like that and and it makes it no longer draggable anymore so that that totally works um and that's that's pretty cool all right so hopefully this was useful if you found it uh if you found this helpful uh and you're curious about more more episodes like this covering different javascript things or messing around with video messing around with apis this is a great place to be and uh yeah you might consider subscribing and turning on those notifications so that you know when new new content comes out right now publishing at a weekly cadence all right thanks everyone and we'll see you next time [Music]
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