CSS Painting API

56 90s_dev 24 5/26/2025, 8:59:06 PM developer.mozilla.org ↗

Comments (24)

jauco · 32d ago

The most fun I had with this was to make initial versions of apps look alpha using https://github.com/pshihn/rough-paint

90s_dev · 32d ago

Amazing example and show-case, great job. Reminded me of my pinstripes:

https://os.90s.dev/#sys/apps/paint.app.js

https://github.com/sdegutis/os.90s.dev/blob/31bf4ec46e02367b...

But yours is much fancier and cooler.

pjmlp · 31d ago

This is part of Project Houdini from Google, it has been years out there without being picked up by other browsers.

https://developer.chrome.com/docs/css-ui/houdini

Anyone remembers the CSS rendering extensions on IE 5?

That's right, the more things change, the more they stay the same.

goranmoomin · 32d ago

If I'm understanding correctly, isn't this introducing a critical dependency on JavaScript during rendering? I get that people might want to draw stuff with code, but why would people use this (and introduce render performance problems inadvertently) instead of using the HTML5 Canvas API?

AgentME · 32d ago

The HTML5 Canvas API can only be used in the main javascript thread, so whenever the page's javascript thread is busy with anything then the browser has to wait on that to finish before being able to have it update anything it rendered. The Paint Worklets allow the browser to run some page javascript just for rendering in one or more separate threads.

MortyWaves · 32d ago

But why can the canvas still only be accessed in the main thread? Why introduce a whole other API as a workaround for this?

Also, as far as I have seen, people have been using WebAssembly for complex stuff and marshalling it to the main thread for the canvas.

AgentME · 31d ago

The worklet API gives the browser the ability to spawn as many threads for the task as it wants when it wants, without needing to communicate and wait on the page's code in the main javascript thread each time.

yladiz · 32d ago

It doesn’t refute your point, because a worklet is a worker and thus not in the main thread, but the canvas API is usable outside of the main thread as well, via OffscreenCanvas or something like transferring to a worker.

90s_dev · 32d ago

We came full circle. We started out overriding draw(), then HTML + CSS took over, and now we're back to overriding draw(). This was a huge inspiration for 90s.dev

reverseblade2 · 32d ago

Here’s a cross browser example I built for my personal site. See the curve: http://onur.works

chrismorgan · 31d ago

That’s badly broken in a variety of ways at a variety of window sizes in both Firefox and Chromium, though worse in Firefox where it goes from being unpleasant to downright unusable at some sizes; and at larger resolutions in Firefox it’s not even managing 3fps. What are you doing? You’re meddling with scrolling, too. :-(

reverseblade2 · 31d ago

I am not seeing any issues on Chrome. To be fair, I mostly cared about Safari and Chrome than Firefox.

Scrolling is about scroll snapping feature.

tyleo · 31d ago

Also broken on iOS. Goes off my viewport horizontally. Scroll doesn’t work as expected.

reverseblade2 · 31d ago

There is scroll snapping. Yes it slightly exceeds the horizontal. My point was about the CSS Painting API though :)

reverseblade2 · 31d ago

Solved the horizontal viewport.

paulryanrogers · 32d ago

Why? Nothing in that article makes the use case clear. Perhaps I just lack imagination?

c-smile · 32d ago

Consider <textarea> that has resizing handle on the corner (try to reply to this message to see it alive). And now try to imagine how would you render those diagonal lines in HTML/CSS ?

While in Sciter, that has such immediate mode rendering form the very beginning, you can simply draw them as:

   resizableElement.paintForeground = function(gfx) { // draw on top of background & content

      let box = this.getBoundingClientRect();
      gfx.moveTo(...); gfx.lineTo(...);
      gfx.moveTo(...); gfx.lineTo(...);
      ...
   }

Easy, right? And does not need to modify DOM and place artificial positioned elements.

andrewingram · 32d ago

A few years ago I tried to use it to implement mesh gradients. It didn’t go well, mainly because you can’t draw individual pixels without cheating with lots of 1x1px rectangles. But it was a fun experiment.

90s_dev · 32d ago

Near the top:

> to set complex custom backgrounds on an element

Basically the same reasons you might need draw() in traditional GUIs.

Do this in CSS: https://camo.githubusercontent.com/b6c45f60f6e450574c4087589...

(image taken from the other guy's comment's gh repo)

dwoldrich · 32d ago

Reusable dynamic canvas code as background image? ¯\_(ツ)_/¯

https://developer.mozilla.org/en-US/docs/Web/API/CSS_Paintin...

hyperhello · 32d ago

But you can do this now with Canvas.toDataURL(). Do we need to support another drawing surface API?

90s_dev · 32d ago

Using toDataURL() has a lot of overhead that this doesn't use. Also this runs in worklets.

Seb-C · 32d ago

Blob URLs should work without much overhead.

esprehn · 32d ago

That won't handle resizing properly. This API lets you hook directly into the painting phase of rendering in the browser so you can both draw the correct size without forcing layout and handle resizing. It also gives the browser the flexibility to not paint the off screen content at all.

Ask HN: How do you learn Spanish guitar?

The 90% Gravity Problem: Why We Tend to Quit Right Before the Finish Line

Ask HN: Startup shutting down, should we open source?

Ask HN: Anyone using augmented reality, VR, glasses, helmets etc. in industry?

Ask HN: Why aren't AIs being used as app beta testers yet?

I built an app to backup Live Photos from iPhone to external hard drives

Ask HN: How would expose a scam involving a powerful figure?

Tell HN: Beware confidentiality agreements that act as lifetime non competes

Ask HN: Why does my Node.js multiplayer game lag at 500 players with low CPU?

Ask HN: How to get rid of Gemini?

Ask HN: What are your peronsal data backup and sync setups?

Ask HN: Alternatives to Cloudflare for DNS?

Strategy or Just a Dream?

Ask HN: Is anyone else just done with the industry?

Tell HN: Meta developer account suspended

Ask HN: Anyone interested in taking over my indie app?

The scam that is Visa Account Updater

Ask HN: If you translate with LLMs, GT or DeepL–what features are missing?

Ask HN: How to regain the ability to read with focus and learn

Ask HN: Why doesn't HN have notifications for replies?

Ask HN: How do you keep your SWE skills sharp outside of work?

184,000 Ray AI Dashboards Exposed Online Without Authentication

Ask HN: How Do You Actually Use Claude Code Effectively?

Ask HN: Laid-off devs who left tech?

Ask HN: Why can't AI fix all open source issues on GitHub?

A literary magazine accessible only via telnet

Ask HN: Why do LLMs call Trump "former president" despite current knowledge?

Are we overfitting our code to trends instead of problems?

CSS Painting API

Comments (24)