A flowing WebGL gradient, deconstructed | Hacker News Reader

A flowing WebGL gradient, deconstructed

alexharri.com

222 pointsalexharri41 comments

>> The mix function is an interpolation function that linearly interpolates between the two input colors using a blend factor between and ( in our case).

>> A mix function for two colors works the same way, except we mix the color components. To mix two RGB colors, for example, we’d mix the red, green, and blue channels.

Colorspace alert! mix != lerp in sRGB

Quite right! I think if the values were linearized (~gamma 0.5) lerp might be mostly ok though, right?

And what about doing rgb->hsv, then lerp, then hsv->rgb? I'm unclear whether that also needs linearization, or whether the gamma can maybe just be done to the 'v' component before lerping?

Color is a surprisingly deep and fascinating topic, that's for sure! :)

Mixing of colors in an "objective" way like blur (lens focus) is a physical phenomenon, and should be done in linear color space.

Subjective things, like color similarity and perception of brightness should be evaluated in perceptual color spaces. This includes sRGB (it's not very good at it, but it's trying).

Gradients are weirdly in the middle. Smoothness and matching of colors are very subjective, but color interpolation is mathematically dubious in most perceptual color spaces, because √(avg(a+b)) ≠ avg(√(a) + √(b))

Perceptual colors -- both sRGB and HSB -- are nonlinear, so you can't expect linear combinations to produce meaningful results (they often "interpolate through mud").

If you just want optical phenomena, you can just convert to luminescence -- WegGL and other modern graphics APIs actually does this internally when you load or render textures, so all shaders are handling optically-linear data, which is why the shader-produced images in the post look better than the javascript gradients.

Googled "luminescence" and OpenGL -- don't seem to return relevant results. Could you point to where it's described?

replace/luminescence/luminance (thanks autocorrect).

Legacy OpenGL APIs used to assume sRGB, so you had to specify GL_LUMINANCE for non-color 'intensity' maps (which couldn't be blitted to FBOs, e.g.).

Modern OpenGL assumes linear color, so instead you have to specify sRGB on texture load to direct the driver to do colorspace conversion (e.g. GL_SRGB8 for typical RRGGBB byte triples).

More info: https://www.khronos.org/opengl/wiki/Image_Format

Luminance[1], not luminescence[2].

[1] https://en.wikipedia.org/wiki/Luminance

[2] https://en.wikipedia.org/wiki/Luminescence

Lol autocorrecttt ty

To be fair, lerp still mixes colors, it just mixes ugly colors.

(1,0,0) and (0,0,1) are each twice as bright, in terms of photons, as (0.5,0,0.5).

If you quickly apply gamma=2 so the midpoint is (0.707,0,0.707) your gradient will look much better. Although other commenters suggested mixing in more complicated colour spaces.

I agree with the colorspace alert. Lerping red and blue in OKLAB or OKLCH colorspace produces a much nicer effect. Also, the article details linear interpolation, but I think there's a lot of fun to be had by introducing some easing functionality into the interpolation[1] - it's not difficult to achieve in code, even in shader code?

I do disagree with the article about the need to do such work in the WebGL space. Modern CPUs are insanely fast nowadays, and browsers have put in a lot of work over the past few years to make the Canvas 2D API as performant as possible - including moving as much work as possible into the GPU behind the scenes. With a bit of effort, gradients can be animated in 2D canvases in many interesting ways![2][3]

[1] - Easing a linear gradient in different color spaces: https://scrawl-v8.rikweb.org.uk/demo/canvas-003.html

[2] - Animated gradient effect: https://codepen.io/kaliedarik/pen/poRLBLp

[3] - Animating a gradient over a live video feed: https://codepen.io/kaliedarik/pen/MWMQyJZ

WebGL/OpenGL doesn't use sRGB in the shaders. If you load an sRGB texture, or render to an sRGB surface, the API automatically applies the gamma- (or inverse gamma) curve, so the shader only ever sees the linear values.

Correct, it uses just numbers without any specific information about a colorspace being involved. Decoding and encoding sRGB happen during (texture) read and write stages.

Very cool, but by css-rotating (skewY(-6deg)) the canvas at the last moment, you introduced aliasing on the border between the canvas and the rest of the page which kills the vibe. The browser can't automatically blend the canvas with the rest of the page. It's noticeable even on a brand new retina display. Maybe you could keep your canvas square and introduce the skew in the shader.

Guess it depends on the browser as it looks sharp and free of aliasing for me, including when zooming in (Opera on Android)

  - Safari: decent but still obviously present
  - Chrome: quite bad looking
  - Firefox: something in between

(tested on macOS)

The funny thing is, as far as I know, skewY is a virtual draw command in the WebKit family of rendering engines.

It's "in the shader" already. For whatever reason, your browser's compositor is failing to anti-alias the rendering bounds of the canvas.

I don't know why, though. I don't see the issue in Safari on my system.

As a workaround, you can add a transparent border (border: 2px solid transparent) around the skewed element to have antialiasing (at least on chrome)

The linked source code [0] doesn't seem to have any license attached to it. So how could I actually use this? Is it published as a package somewhere, like npm?

0. https://github.com/alexharri/website/blob/eb9551dd7312685704...

Hmm, good point. I’m abroad this week and don’t have a laptop, but I’ll look at adding an MIT licence to the shader itself when I’m home. (I don’t want the post contents to be MIT licensed, but the website code and examples should be)

Thanks for raising this

This effect kinda reminds me of the PSP menu background

We need more articles as polished as this one. WebGL is a topic I wanted to get into for a while now but it's really difficult to find good content about it. Please keep sharing more experiments!

Could not agree more. Heard good things about https://webgl2fundamentals.org/, but I think it directly jumps into code without any background as such. At least that is what I felt. Not sure whether this is the only way to go about teaching WebGL.

Thanks for sharing this one. I was looking for more material too!

Jesus christ, this is such a polished article. Writing it must have taken at least 5 times as long as the shader!

Have reblogged it and will refer back to it if ever I have some time to learn how to write them :)

Thanks a lot! Yeah tons of work went into this post, I’ve been working on it since November. The shader itself was about 2-3 weeks of evenings to get the effect 90% of the way

This is so cool. These flowing gradients have a mesmerizing effect (almost like watching a lava lamp), and seem like a great way to add visual interest to a page. I'll have to play around with this and see if I can incorporate these flowing gradients into some of my web projects. Awesome job detailing the design process for this post.

The whole time I was expecting just a 2d height field ("terrain") with animated noise as z, overlooked from an angle by an isometric camera, it could imo produce a same effect in a much simpler way (and without need for expensive blur), right?

The blur here isn't expensive (as discussed in the article itself).

Chances are sampling a 2D height field and projecting, etc. would be more expensive.

Nice, it's a bit like an extremely modern version of the oldskool plasma effect!

This looks very smooth. Would this be in 10 bit colour if the display supports it? I can't see any banding even when zoomed in Safari or Brave on a MBP with HDR display.

Looks pretty nice. I think there'd be a way of computing the blurriness without the iterative approach and without the aliasing produced in the process.

This is an exemplary post and what I come to HN for.

Great post Alex, the gradients are lovely, I'm just starting to play around with webgl so the timing is perfect ...

This is a great read. Very instructional. Build from simple concepts and explain clearly. Kudos for the work.

Reminds me of the JetBrains installer--not a bad reminder, I like the animations.

This is an excellent article. Thanks for this.

Fantastic post, very well written.

Amazing writeup, very inspiring!

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