Item — HN Reader

There's a lot of Google negativity here (perhaps not without reason), but when you view the AMP spec and what it tries to solve for, it feels like a smart move to help broaden the adoption of sensible but poorly understood optimizations: https://www.ampproject.org/docs/get_started/technical_overvi...

Those optimizations are worth looking over even if you don't plan on adopting AMP.

I do think that rather than requiring direct use of AMP for specialized search placement, it should really measure site performance and only ensure your site meets the same benchmark, no matter what you do to optimize.

Google may not be a perfect ally of the open web, but I like this approach much more than what I've seen from Facebook.

3 comments

Google has repeatedly said that they will not give preferential treatment for AMP pages. Almost every publication [1] and comment I've seen gets this wrong.

According to official comment, the ranking algorithm will prioritize page speed, and AMP is a good way to achieve that.

BloombergBusiness uses some questionable sentence structure in order to imply the opposite, but that's on them:

  AMP isn’t “a signal we use in ranking” pages, Besbris said. 
  He declined to comment about whether AMP pages would rank
  higher, though he said some of the signals Google uses for 
  search include whether a page is mobile friendly and how 
  rapidly it loads -- two problems that AMP seeks to tackle.

[1] e.g. http://adage.com/article/digital/google-amp-launch-looms-sea... See their retraction at the end of the article.

Some of those guidelines (avoid style recalculation and use only "GPU-accelerated" animations) are specific to Chrome (and to other browsers of today). Style recalculation is needlessly slow today due to the lack of parallelism and typed CSSOM. And there's no such thing as a "GPU-accelerated" animation, either in the spec or technically: all animations can be run on the GPU with minimal state changes. It's just that browsers found it easiest to only optimize a small subset of cases (in the case of CSS animations, really small--transform and opacity), so as to keep around their legacy, originally-CPU-based, painting infrastructure. It's good that they did that, because it let us get to some degree of graphics acceleration quicker, but we can do so much better.

I'd prefer to just improve the browsers instead of putting the burden on Web authors.

I think the browser specs are broken such there will always be pathological cases, and always cases where 'you're on the performance rails'. End users don't care.

This is no different on any other platform. If you program games directly to OpenGL, for example, you run into all kinds of different bottlenecks, both CPU and GPU. Depending on the pipeline of the various GPUS, and what kinds of hazards they have, there's stuff you have to avoid, or branching paths you have to handle to get good performance. If you use SQL databases, not all databases can handle all queries optimally.

I think it is asking too much of browsers to give them such a huge surface area spec as HTML and CSS, and then ask for them to optimize everything so there's no slow paths.

The practical reality is, there's always a subset of specs known to be fast and well supported and developers just need to know what that is.

> I think the browser specs are broken such there will always be pathological cases, and always cases where 'you're on the performance rails'. End users don't care.

In the case of GPU acceleration, the specs are not broken. There is no fundamental reason why animations on arbitrary properties cannot be GPU accelerated and some can be. Ask anyone who's worked with Scaleform whether rapidly changing vector graphics (which is all these animations are) has to be slow on mobile.

For style recalculation, maybe, maybe not; it's not clear to me that browsers are worse than native app frameworks here, except that we're missing Typed CSSOM, which is important spec work.

> This is no different on any other platform. If you program games directly to OpenGL, for example, you run into all kinds of different bottlenecks, both CPU and GPU. Depending on the pipeline of the various GPUS, and what kinds of hazards they have, there's stuff you have to avoid, or branching paths you have to handle to get good performance.

And game engine authors are fed up with it, which has led to Metal, DX12, and Vulkan. It's not a good way to treat developers; we should try to give them APIs in which, as much as possible, everything is fast. I think the Web APIs can be that, if implemented optimally.

> I think it is asking too much of browsers to give them such a huge surface area spec as HTML and CSS, and then ask for them to optimize everything so there's no slow paths.

I'm not saying that we have to pretend everything in HTML and CSS can be made equally fast. My point is that, in many areas, browsers have done a bad job of even trying to optimize broadly. Take animations, for example: the only thing browsers optimize is two properties out of hundreds, transform and opacity. This is exceptionally problematic, given that there's no technical reason why this has to be the case. I just gave a talk about this a few days ago :)

I think you have a different idea of what gpu acceleration means here. When we say that animating transform and opacity is fast, it means that we can animate it without rasterizing content over and over again i.e. only use composition. This is independent of how rasterization takes place. Rasterization itself can be gpu accelerated, Chrome has started doing this on mobile[1].

Animating other CSS properties such as font-size require us to rasterize new content on every frame of animation. That is the inherent reason for why it's slow. Again we can use the GPU for rasterization but we're still going to do it every frame instead of caching the result in a texture that's then composited over and over again.

[1]: https://www.chromium.org/developers/design-documents/chromiu...

I know how it works. I wrote much of the layout and graphics code for Servo and did the initial bringup of the compositor on Firefox Mobile. You shouldn't have to rasterize new content on every frame when you animate font-size (except for individual glyphs, but that's still quick, just a few ms, if you parallelize it—and even with techniques like SDFs and/or GPU vector graphics tricks like [1] you may not even need to do anything on the CPU). If you animate, say, margin-left, you should in most cases be doing essentially no work on the CPU, and you should be able to submit one draw call to repaint the page since all of the resources (images, glyphs, alpha masks, SVGs) should be cached in an atlas. It should be 1-2ms. Even animating something like border-top-width should be no resource changes and one draw call, exactly as fast as your compositor should do it.

Optimally implemented, I believe there should be no difference between "rasterization" and "compositing". You're painting the same number of pixels, paying the same fragment shading and rop cost, either way. Caching fully rendered Web content in textures assuming that the cost of rasterizing that content is high isn't working very well, and I think it's not worth it.

[1]: http://wdobbie.com/post/gpu-text-rendering-with-vector-textu...

Does using a font-atlas really deliver the same quality as fully hinted true-type fonts? Also, this demo doesn't really have any state changes in it. Wouldn't a more realistic example be of a UI that contains mainly different font weights and sizes, to better gauge the effects of all of the pipeline state changes.

I agree that the browser should be more like a game engine, and less like an X11 buffered window system, in terms of just rasterizing faster enough to render 60fps. But it seems like to me that the CSS spec contains a number of features (rounded corners, soft shadows, etc) that by themselves can be rendered fast on a GPU, but cobbled together in a complex scene graph might result in stalls.

> Does using a font-atlas really deliver the same quality as fully hinted true-type fonts?

Hinting really isn't important on mobile or HiDPI. In fact, no version of OS X or iOS does it. (I don't know about Android, but I wouldn't be surprised if it doesn't on HiDPI screens.)

What's more interesting is antialiasing quality, especially subpixel AA. That's something I think needs more investigation. But I'm cautiously optimistic; there's been some really exciting work in GPU AA and vector graphics lately :)

> Wouldn't a more realistic example be of a UI that contains mainly different font weights and sizes, to better gauge the effects of all of the pipeline state changes.

Don't change state then. :)

State changes really shouldn't be necessary. If you set things up properly, you should be able to render arbitrarily many glyphs with one draw call, bound only by your texture atlas size.

> But it seems like to me that the CSS spec contains a number of features (rounded corners, soft shadows, etc) that by themselves can be rendered fast on a GPU, but cobbled together in a complex scene graph might result in stalls.

They typically don't. The key is to render critical resources like that to a texture atlas and to batch like resources together as you do so. (For example, batch all box shadow pieces together into one draw call, batch all rounded corners into another, etc.) This effectively places a small fixed upper bound on the number of draw calls you issue. Then you can rerender the page for each animation frame with a very small number of draw calls (frequently just one) and a simple blitting shader. If you get your draw call/state change overhead down, essentially nothing on the Web comes close to taxing a modern GPU; GPUs are incredibly fast at rendering batches.

My talk goes into more details, if you're curious: https://air.mozilla.org/bay-area-rust-meetup-february-2016/

You know, I think it would be great if web browsers fixed things. AMP is fixing a very real problem that users have today.

If and when browsers change (including those used by a lot of people that only update once a year) AMP can just change its guidelines. These are things people have to do today anyway to get fast sites. AMP just packages up in an easy to consume package.

Sure, I'd love browser improvements too, but at the end of the day, you can't automatically optimize everything from the browser. The browser can't magically fix a 1MB JS file in <head>, or serving 2000px wide images to iPhones.

>I'd prefer to just improve the browsers instead of putting the burden on Web authors.

A cynical answer is that Google released this because web authors haven't done a good enough job making fast pages.

> Sure, I'd love browser improvements too, but at the end of the day, you can't automatically optimize everything from the browser. The browser can't magically fix a 1MB JS file in <head>, or serving 2000px wide images to iPhones.

Sure, I agree that many of the optimizations suggested are good practice.

(Note, though, that serving 2000px wide images to iPhones is fixable in the browser, with downscale on decode.) :)

> A cynical answer is that Google released this because web authors haven't done a good enough job making fast pages.

It's not cynical—that's the exact motivation of AMP. My point is that it cuts both ways: we need to keep improving the browser, as there are still massive opportunities for performance improvements.

> (Note, though, that serving 2000px wide images to iPhones is fixable in the browser, with downscale on decode.) :)

From a rendering perspective, yes. From a "make this page load faster", no, because the network download time is 10x-100x larger than the processing time.

All CSS must be inline and size-bound

Does this mean that only inline styling is supported? <div style="..."> Or just that styling should be included on the page in a <style> tag.