Very slow operation in 11.2.0 and higher with large blocks, using "sizeToContent" and crippled cellHeight values

[IgorA100]

Subject of the issue

I need all the blocks to be placed close to each other (maximum distance should not exceed 2px) and "sizeToContent" should be used. For this I used cellHeight: '1px' || '2px' and everything worked fine for both small and large blocks. With other cellHeight values, the distance between the blocks vertically will be large.
Up to version 11.1.2 (inclusive) I had no problems with initialization:

Starting with version 11_2_0 and up to 11.4.0, terrible slowdowns begin during initialization. If I specify cellHeight: '50px' or I do not specify cellHeight, then everything will work quickly, but there will be a gap between the blocks vertically.

Your environment

• version of gridstack.js - 11.1.2 & 11.2.0 & 11.4.0
• which Chrome, Chromium/Windows 8.1, 10

Steps to reproduce

This behavior cannot be simulated on jsfiddle.net, because it requires a large browser window.
On the HTML page, create more than 15 image blocks of size 3840x2160
Expand the browser window to full screen.
and after the page loads, initialize:

window.onload = function() {
  const opts = {
    margin: '0px',
    cellHeight: '1px',
    sizeToContent: true,
    column: 48,
  };
  var objGridStack = GridStack.init({...opts});
};

Attached is an archive that you can deploy on your server and check the execution speed. In the index.html file, you can connect either 11.1.2 or 11.4.0
gs.zip

Expected behavior

The speed of initialization in 11.2.0 and subsequent versions should not be several (3-10) times lower than in 11.1.2
"addCSSRule" in GS works very slowly

[adumesny]

GS wasn't designed to use cellHeight:1px as ton of CSS will be created and collision isn't ideal, but large chunks of blocks for things to line up. maybe use another lib ?

that said, sounds like 11.2 changed the CSS creation and is now slow... I could take a look, but other issue might crop up that won't be fixed...

this is most likely caused by #2852
@lmartorella do you have a suggestion ? suppose we could make the change to #2854

[IgorA100]

GS wasn't designed to use cellHeight:1px

But what to do with this? #2979
What if you want to avoid empty space?
Before version 11.2.0 everything worked fine!
cellHeight:1px is of course rare, but for example cellHeight:5px is a very real value. And with 5px there are also terrible slowdowns...

maybe use another lib ?

:) This is not the best suggestion...

but large chunks of blocks

I just checked on 200x200 images, also terrible slowdowns... Doesn't depend much on the size. Depends on the cellHeight values

[lmartorella]

Hi,
Yes, you should definitively look to integrate #2854 to avoid stylesheet manipulation at all. Scenarios like this one, with many rows, would benefit in not having O(N) CSS classes where N = rows.
Yes, it is possible that #2852 without #2854 causes performance issues, so if you are not planning to integrate #2854 soon I would revert it.
Thx, L