975741 - initial value of 'perspective' should be stored as 'none' rather than '0', and computed style should not work around the invalid storage

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Right now we internally implement the initial value of perspective as '0' rather than 'none', although we allow an explicitly-specified 'none' to reflect its way through our internal representation.  Then we fix up the value in nsComputedDOMStyle to report a '0' as 'none' to hide the other bugs.

We don't have any differences in behavior between the '0' and 'none' values (I checked).  But:

 (1) it's a minor spec conformance bug, in that we don't properly reflect '0' as different from 'none'

 (2) we will likely want to add some internal differences in behavior, for example, for bug 968555; having this data incorrect internally seems likely to things being implemented incorrectly in the future

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: Make the initial value of 'perspective' be 'none' rather than '0', and make the nsComputedDOMStyle computed value implementation of 'perspective' properly distinguish between '0' and 'none'.

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Er, I said that backwards in both the bug summary and the patch description.

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Oops, I missed the fact that 'perspective' only allows positive values, so the summary of the bug should be slightly different, and I need to change the test to list '0px' in invalid_values.  But the patch is fine as-is, and still simplifies the code and makes the storage of identical values more consistent.

(Though we can also remove the >0 checks now, actually.

Comment 4

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/22a2eb6d2145

Comment 5

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: patch 2: Remove checks of nsStyleDisplay::mChildPerspective.GetCoordValue() > 0 because it's now always greater than 0.

Now that the first patch in this bug changed things so that 'none' is
reliably stored as eStyleUnit_None (rather than being stored as a 0
length when it comes from the initial value), we know mChildPerspective
is always > 0 when it is eStyleUnit_Coord, and there's no point making
the additional check.

Comment 6

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/22a2eb6d2145

Comment 7

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/e8eaec0c9198

(and previous try run at https://tbpl.mozilla.org/?tree=Try&rev=49d369b164bb)

Comment 8

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/e8eaec0c9198