[Webkit-unassigned] [Bug 163790] New: font-variation-settings at or beyond axis extremes result in the axis reverting to default

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https://bugs.webkit.org/show_bug.cgi?id=163790

            Bug ID: 163790
           Summary: font-variation-settings at or beyond axis extremes
                    result in the axis reverting to default
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Macintosh
                OS: macOS 10.12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: lorp at lorp.org
                CC: mmaxfield at apple.com

Created attachment 292357
  --> https://bugs.webkit.org/attachment.cgi?id=292357&action=review
HTML (with a bit of PHP) to show how some values close to axis extremes revert to default. The $makesafe variable is a toggle which ensure values are within the range

Using font-variation-settings beyond axis extremes results in the axis reverting to its default. Sometimes using font-variation-settings *at* axis extremes results in the same undesirable behaviour. Settings at or beyond the extremes should (surely?) be clamped to that extreme.

To replicate the bug, try Skia, which contains the following raw data in the fvar table (min, default, max):

wght: 00007AE1, 00010000, 00033333 = 31457, 65536, 209715
wdth: 00009EB7, 00010000, 00014CCC = 40631, 65536, 85196

These correspond to the extremes, expressed in CSS:

font-variation-settings: 'wght' 0.47999572753906, 'wdth' 0.61997985839844;
font-variation-settings: 'wght' 3.1999969482422, 'wdth' 1.2999877929688;

These settings do not result in expected behaviour. In particular the 'wght' seems to become default. Subtracting 0.0001 from the max weight does not fix the problem, however subtracting 0.01 does fix it. See the difference by using the $makesafe toggle in the attached PHP file.

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