In this case, VSCode is probably using the most reasonable approach to blinking a cursor: a `step` timing-function with a CSS keyframe animation. This tells the browser to only change the opacity every 500ms. Meanwhile, Chrome hasn't yet optimised this completely yet, hence http://crbug.com/361587.

So currently, Chrome is doing the full rendering lifecycle (style, paint, layers) every 16ms when it should be only doing that work at a 500ms interval. I'm confident that the engineers working on Chrome's style components can sort this out, but it'll take a little bit of work. I think the added visibility on this topic will likely escalate the priority of the fix. :)

* Simple text editors, and basic ones built on [contenteditable] can, but those rarely scale to the feature set most want.

(I work on the Chrome team, though not on the rendering engine)

Only? It shouldn't be necessary to layout the entire window to redraw a cursor.

Also, if it did update every 500ms:

- it still would use about half a percent of CPU. On a machine whose CPU easily is >200 times as fast as those powering the first GUIs (and those _could_ blink the caret at less than 100% CPU) and that has a powerful GPU, that's bad (yes, those old-hat systems had far fewer pixels to update, but that's not a good excuse)

- implementing smoother blinking (rendering various shades of gray in-between) would mean going back to 13% CPU.

I would try and hack this by layering an empty textfield on top of the content, just to get a blinking caret. Or is it too hard to make that the right size and position it correctly?

Is there any reason that Electron couldn't provide an API that would expose the system caret in an OS-agnostic manner? Windows, for example, has an API[0] that can arbitrarily show the caret at a given point in the window. Sounds like something that would be useful to many apps and not get in the way for those that don't need it.

[0] https://msdn.microsoft.com/en-us/library/windows/desktop/ms6...

My favorite issues was that on one OS (windows I think) a panel would only be visible if pixel 0,0 was on the screen and nothing was on top of it. The panel could be 99% visible but not be shown at all if the upper left corner was under another panel.

(This is a perfect example of what I've been increasingly convinced of lately: that the whole "paint"/"compositing" distinction hurts the Web…)

Can you explain in simple terms why this is the case? Why on earth not?

Does that answer your question? :)

Reported almost 3 years ago and still not fixed...

I'm guessing the culprit for that is in this part of the bug report:

> Zooming into a single frame, we see that while we render only 2 fps, the main thread is performing some work at 60 fps (every 16 ms)

As for

> why they needed to implement it themselves and not let the OS handle the blinking cursor

They're not editing inside a text editor field anymore, they need to blink on html. I guess they're not using a deprecated <blink> tag is because it's not customizable in any way.

I'm sure other operating systems have this kind of facility - after all, how does the built in text edit control draw its caret?

[0] https://msdn.microsoft.com/en-us/library/windows/desktop/ms6...

The "built in text edit control" IS a native text field already.

No need to have an official OS caret function (especially if you're not a native text field, and caret aside, the rest of your text editing will be different/broken in subtle ways compared to the OS).

Certainly, on the original Mac OS (a system on which I worked on OS patches for detecting the location of the caret) the method that application used for drawing the caret varied widely. I've seen it implemented by drawing a line, by drawing a rectangle, either in one go or in two parts (that happened in applications that supported a split caret, even if the caret wasn't split), with various transfer modes. Slanted carets typically were application-specific, too.

Windows allows this. In a parent comment I posted a link to the API docs. All Windows requires is a window to hold the caret, it doesn't care what kind of window it is.

Probably because they are using electron.

I made a webpage based on a bootstrap template

On this webpage, I have 2 realtime components. one is a chart, based on dygraphs

the other component is a bootstrap progressbar.

the bootstrap progressbar is made by html divs:

https://www.w3schools.com/Bootstrap/bootstrap_progressbars.a...

Both components are updated in realtime by a websocket.

I noticed that the chart by itself is very fast. But as soon as the progressbar is added, the entire webpage and even the entire machine becomes very slow. I guess this is because every bit of progressbar update, the browser rerender the entire page, as the progressbar is a div.

I don't know how to solve this. I thought about using react for its virtual dom. but if eventually I need to update the dom, the speed seems to be the same.

Lodash has a debounce function which is useful to throttle UI features hooked to incoming data. https://css-tricks.com/debouncing-throttling-explained-examp...

You never really want the UI repaint to be dictated by data, it's better to use timers.