That's because transparency limits how you can batch draws on the GPU. With opaque draws, you can use the depth buffer and draw in any order you like e.g. maximizing batching. With transparency, you need to draw things in the right order for blending to work (painters order).
Chromium in particular tries to minimize the total number of layers. It renders each layer into a pixel map, then for each frame it composites all of the visible layers into the final image.
That works really well in practice because you often have lots of layers that move around but don't actually change their pixels. So those don't need to be rendered (rasterized) every frame, just composited.
If you have a bunch of box shadows without transparency, Chromium will rasterize the whole thing once as a single layer.
If you have a bunch of box shadows with transparency, Chromium might create a separate layer for each one. That's probably suboptimal in this particular case, but imagine if your partially transparent box shadows had to also slide around the page independently.
Games draw every single object on the screen every frame. They don't lag, quite the opposite in fact!
Start with a buffer that's fully transparent (α=0.0)
for each face from front to back:
for each pixel of the face:
draw the pixel, blending 1.0-buffer.α of the new pixel into whatever's already in the buffer
(if buffer.α == 1.0 you can just skip it entirely, just like for depth buffering)
go back and double check your math relating to transparent objects behind other transparent objects
It is generally good to render opaque geometry back to front to reduce overdraw, but not going so far as sorting the objects. We would do stuff like render the hands first in an FPS or render the skybox last in most games.
Now for the transparent layer: First occlusion is handled by the z-buffer as usual. If you render from front to back I assume you render to another buffer first and then composite to the framebuffer? If you render from back to front you don't need alpha in your framebuffer and can assume each rendered pixel is opaque, not needing that composite.
There's also order independent transparency stuff though which IIRC does need another buffer, which requires a composite but then saves you having to sort the objects.
It isn't like the Ps2 era when geometry time was a real concern on render times. Even a modern low end GPU could process a few hundred million polygons a second without sweating it, now getting the result son screen is a very different issue.
If you're doing non-overlapping stuff, you'd actually expect (almost) no slowdown from transparency, since you'd have to touch every pixel once anyway, and the only thing that changed is the shader formula.
A non-transparent draw over another draw allows in best case to cull all overlapping drawing operations, in worst case means you only have to use as much bandwidth as the individual draws.
With transparency, especially if you can't somehow combine the operations together (from my understanding, very hard problem), it means you also need to read back the entire region you're overlapping with transparency - so every transparent draw involves at least twice the final framebuffer size bitmap going-over memory bus.
Now consider that many mobile devices had not enough memory bandwidth to do a full redraw (i.e. blit the full framebuffer image twice) of the screen in time to maintain 60fps and it becomes a considerable problem.
> Layering. That is an important word.
Layering is also the key to the (silly but also sometimes good-looking) effects from my text shadow project from 14yrs ago: https://paulirish.github.io/mothereffingtextshadow/
It's almost like this post has many layers to it, and that it's not really about box shadows.
Switched to Chrome - suddenly everything is butter smooth.
Congrats on an article very well done!
Which isn't to demerit the hackish creativity of taking one thing and running with it! But if you wanted to do a ball painting effect like that outside this "what if" context, it would be technically irresponsible to do it with box-shadows.
AVS and Milkdrop could probably run on a toaster today, I'd guess even WebGL would be enough on a smartphone, laptop or similar device with some kind of GPU.
Meanwhile, YTM costs 13€ a month, doesn't have an equalizer, no cross-device sync despite cloud everything... no nothing. Not even gapless album playback.
Once upon a time, I signed up to Spotify in order to have a good conscience, because I grew old and didn't want to keep collecting audio files...
Then Spotify became worse and worse.
For now YTM seems like a better deal, but I still can't even find a free solution to migrate my playlists.
Basically, everything went to shit. The only advantage is not having to illegaly download new music after browsing Discogs.
The disadvantage is, apart from the odd good recommendation, my interest in discovering new music has vanished.
Even new music found on Discogs.
But why bother saving songs to playlists when it's all transient anyway?
That was my main last straw with Spotify — too many good music disappearing from playlists, and steadily worsening recommendations. With rabbit-holes of totally trash AI-generated "music" in between, that didn't stop unless actively skipping.
And YTMs not gonna end any better, I feel.
Just a reminder that all music is transient. And maybe to seek regaining enthusiasm by playing music myself, or going out.
Streaming really has killed "listening to music" and being excited about it for me, and I don't feel it's purely because of old age.
Going to revive my Mp3 collection soon from a backup and download my ~25 records worth listening since 2012 then from Bandcamp instead.
Any references to learn more about these hacks?
A modern 3D accelerated article (using SDF as another commenter suspected) https://mortoray.com/quickly-drawing-a-rounded-rectangle-wit...
Have to add work by Evan Wallace here too as he is a legend.
https://madebyevan.com/shaders/fast-rounded-rectangle-shadow... https://madebyevan.com/webgl-path-tracing/
So hard.
Basically the same reason pet veterinaries and teachers and nurses and musicians and artists still attract plenty of candidates despite a comparatively low pay.
(Playing games is more fun than working with CRUD apps. But writing games and writing CRUD apps seem about equal in their probability distributions of fun.)
Why would I know it? It's CSS!
For me it's not that it's freezing, it's that the page scroll stops responding.
I can get the tab back by cutting the URL, closing the tab, opening a new tab, pasting the URL, then scrolling to where I want to keep reading from.
It seems to render everything fine if you don't mind scroll stopping (ahem).