[css3-flexbox] Should "align-self:stretch" have any effect on main-size? (i.e. should stretched cross-size be used for establishing main size?) (original) (raw)

Hi www-style,

Question: Should "align-self: stretch" on a flex item (stretching it in the cross axis) be able to have any effect on a flex item's main size? (in the absence of any intrinsic-ratio effects)

From my reading, the answer from the current flexbox ED is "no" -- the spec's algorithm first establishes the main size of flex items and of the flex container (in section 9.2 through 9.3), and it only takes "align-self:stretch" into account when we're midway through section 9.4. But Chrome and Opera don't seem to match my expectations, and I like their behavior & think we might want to amend the spec to explicitly call for their behavior.

Consider this testcase: http://people.mozilla.org/~dholbert/tests/flexbox/can-stretch-affect-main-size-1.html

That testcase contains two examples, which only differ in their "align-items" value on the outermost (vertical) container.

In Chrome & Opera, the first example (the one with "stretch") has a reduced height (main-size) with respect to the second example (the one with flex-end.)

I think this is incorrect, per spec (as noted in my 2nd paragraph above). However, I think the behavior makes sense; if we know up-front that we're eventually going to be stretching a vertical flex item's width, and we can compute what its stretched width will be, and we have to do a trial layout to establish a hypothetical height, then I think it makes the most sense to do that trial layout using the stretched width. I'm guessing that's what Chrome and Opera are effectively doing, though I'm not sure.

We could make this change by extending this existing spec text, from section 9:

For the purposes of these definitions, a definite size is [...]

If a single-line flex container has a definite cross size,

any flex items with �align-self: stretch� must also be treated

as having a definite cross size

http://dev.w3.org/csswg/css-flexbox/#layout-algorithm

This chunk is just defining what "definite" means; it's not mandating that we use this "definite" size for laying out our flex item. But I think it, or the spec text following it, should be amended to actually call for using the stretched cross-size when establishing an item's main size, under the conditions laid out in the spec-text quoted above. (single-line container, with definite cross size)

Thoughts?

Thanks! ~Daniel

Spec reference:

Received on Tuesday, 20 August 2013 06:28:35 UTC