[css-grid] Unclear how to limit track growth by fit-content() argument · Issue #4549 · w3c/csswg-drafts (original) (raw)

From https://drafts.csswg.org/css-grid/#algo-spanning-items,

• For max-content maximums:
  Lastly continue to increase the growth limit of tracks with a max track sizing function of max-content by distributing extra space as needed to account for these items' max-content contributions. However, limit the growth of any fit-content() tracks by their fit-content() argument.

The last sentence could be applied in different ways, I can see 2 reasonable options:

• Option A: In https://drafts.csswg.org/css-grid/#extra-space run step 2 as normal, but at step 3 'Update the tracks' affected sizes' clamp the planned increase, i.e.

affectedSize += plannedIncrease  

becomes

affectedSize += clamp(0, plannedIncrease, fitContentArgument - affectedSize)  

• Option B: impose this limit during step 2.
  The 'Distribute space to base sizes up to growth limit' is not affected, it's no-op since the affected size is a growth limit in this case.
  During 'Distribute space beyond growth limits', when it says

  when handling any intrinsic growth limit: all affected tracks.
  actually only distribute among the tracks that are still treated as having a max-content max track sizing function, and stop distributing once they reach their fit-content() argument and start being treated as fixed.

With both options we may end up not distributing all the space (all tracks could have fit-content(0)). The difference is that with option A we are more likely to distribute less space, while in B we will fallback to distributing to other tracks if possible.

Actually I don't really understand what the spec is trying to do by limiting the growth by the fit-content() argument only when dealing with max-content maximums, but not for intrinsic maximums. I also wonder whether 'Distribute space to base sizes up to growth limit' should freeze when a base size reaches a fit-content() argument smaller than the growth limit, and leave further increases for 'Distribute space beyond growth limits'.