Bug 16020

Summary: A transition of width: auto to a fixed width computes auto as zero.
Product: WebKit Reporter: Timothy Hatcher <timothy>
Component: CSSAssignee: Nobody <webkit-unassigned>
Status: RESOLVED WONTFIX    
Severity: Normal CC: arv, bdakin, bosselmann, cedricv, chriscoyier, dglazkov, dino, farukates, felixcca, humaknlght, hyatt, jarred, jcraig, joe, jonathon, jscinoz, kimmo.t.kinnunen, lamargoddard, mathias, michael, mihaip, mjs, mkozakewich, rboucher, rik, samtsai, simon.fraser, s+webkit, webkit, webmaster
Priority: P2 Keywords: InRadar
Version: 528+ (Nightly build)   
Hardware: All   
OS: All   
Bug Depends on:    
Bug Blocks: 46590    
Attachments:
Description Flags
Testcase
none
Test case from related Radar, includes both % and auto widths. none

Description Timothy Hatcher 2007-11-16 14:25:23 PST
A transition of width: auto to a fixed width computes auto as zero. See attached test case.
Comment 1 Timothy Hatcher 2007-11-16 14:25:46 PST
Created attachment 17321 [details]
Testcase
Comment 2 Dave Hyatt 2007-12-14 18:31:11 PST
This is tricky, since animation happens on RenderStyles, so a layout would actually be required in order to determine what the auto width value at the destination is going to be.
Comment 3 James Craig 2008-02-20 13:15:10 PST
Adding Radar I filed a while back.
<rdar://problem/5639997> transition fails when animating between different size units (e.g. px and %)
Comment 4 James Craig 2008-02-20 13:19:01 PST
Created attachment 19236 [details]
Test case from related Radar, includes both % and auto widths.

Adding test case from related Radar, includes both % and auto widths.
Comment 5 mitz 2008-04-25 08:40:06 PDT
*** Bug 18726 has been marked as a duplicate of this bug. ***
Comment 6 Simon Fraser (smfr) 2009-01-09 17:44:21 PST
<rdar://problem/5639997>
Comment 7 Simon Fraser (smfr) 2009-02-27 10:29:14 PST
Comment from Dave Hyatt on the w3-style list:

This is right.  In WebKit, we transition on the computed value of a property (not the specified value or used value).  Note that there have been requests to transition on the used value instead, the most obvious example being wanting to transition from, e.g., width:100% to width:50px.   If you transition on the computed value, then it's impossible to run an animation from width:auto to width:50px or from width:50% to width:80px, etc.

The problem with transitioning on the used value, though, is it can change when your style hasn't.... if you resize a window that contains a width:auto or width:100% block for example.  Obviously you don't want to run a transition in that case.

My own preference would be (for simplicity) to just stick with transitioning on the computed value and to just say "Tough" to people who want to animate width this way, but maybe others disagree.  We continue to get bugs in WebKit from confused people trying to animate auto widths to fixed values (or percents to fixed values) and not understanding why it doesn't work.
Comment 8 Michael Kozakewich 2009-11-29 15:03:26 PST
*** Bug 31957 has been marked as a duplicate of this bug. ***
Comment 9 Maciej Stachowiak 2010-01-07 14:13:47 PST
How about we animate on the used value but only when the computed value changes?
Comment 10 Faruk Ates 2010-01-07 14:53:11 PST
Isn't the computed value internally kept as a pixel value no matter what the unit is? Wouldn't that mean that a change from width:80px to width:auto could do a non-transitioned lookup to see what pixel value "auto" currently computes to, and transition to that?

I'm probably not understanding it, but it seems weird that every Javascript library in the world that does this has it figured out, but a hardware accelerated implementation can't?
Comment 11 Sidney San Martín 2010-01-20 08:58:29 PST
> My own preference would be (for simplicity) to just stick with transitioning on
the computed value and to just say "Tough" to people who want to animate width
this way, but maybe others disagree.

Many use cases for CSS transitions and animations include starting and ending at a computed value — showing and hiding content is a huge one.

Also, treating computed values as zero is never going to be the right behavior. If this isn't going to be fixed, then trying to animate a computed property should kill the animation entirely.
Comment 12 Faruk Ates 2010-01-20 09:45:47 PST
I think not fixing this bug would be a grave mistake; this is the #1 use case for animation libraries used on the Web today, and thus, the #1 use case for the CSS Transitions implementation. And it is broken in CSS Transitions.
Comment 13 Simon Fraser (smfr) 2010-09-27 14:17:09 PDT
Dave Hyatt and I talked about how we might fix this. We'd have to do a layout at the start of the animation to compute the end state, but this might not work in some cases.
Comment 14 Simon Fraser (smfr) 2010-12-01 12:08:20 PST
*** Bug 35816 has been marked as a duplicate of this bug. ***
Comment 15 Simon Fraser (smfr) 2011-01-11 20:13:01 PST
*** Bug 52245 has been marked as a duplicate of this bug. ***
Comment 16 Simon Fraser (smfr) 2011-02-24 10:59:12 PST
*** Bug 55137 has been marked as a duplicate of this bug. ***
Comment 17 Sam Tsai 2011-04-27 11:15:48 PDT
Has there been any progress on this bug? Or are there alternate solutions that we could work towards?
Comment 18 Simon Fraser (smfr) 2011-07-25 12:16:03 PDT
*** Bug 65067 has been marked as a duplicate of this bug. ***
Comment 19 Nikita Vasilyev 2013-08-27 20:12:20 PDT
*** Bug 113871 has been marked as a duplicate of this bug. ***
Comment 20 Simon Fraser (smfr) 2016-05-02 18:00:48 PDT
The CSS WG has resolved that transitions don't run to/from auto values.
Comment 21 Joe Pea 2017-03-14 12:59:03 PDT
This resolution is very frustrating.
Comment 22 Joe Pea 2017-03-14 12:59:57 PDT
The web keeps disappointing. Are you browser devs really okay with that?
Comment 23 Simon Fraser (smfr) 2017-03-14 13:35:42 PDT
(In reply to comment #22)
> The web keeps disappointing. Are you browser devs really okay with that?

Please bring this up on www-style if you think it's important.