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Alter layout engine to conform closer to W3C spec

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The primary goals of this change are:
  - Better conformance to the W3C flexbox standard (https://www.w3.org/TR/css-flexbox-1/)
    and a clear articulation of the areas where it deviates from the spec.
  - Support for flex-shrink.
  - Conformance with layout effects of "overflow: hidden".

Specifically, here are the limitations of this implementation as compared to the W3C
flexbox standard (this is also documented in Layout.js):
  - Display property is always assumed to be 'flex' except for Text nodes, which
    are assumed to be 'inline-flex'.
  - The 'zIndex' property (or any form of z ordering) is not supported. Nodes are
    stacked in document order.
  - The 'order' property is not supported. The order of flex items is always defined
    by document order.
  - The 'visibility' property is always assumed to be 'visible'. Values of 'collapse'
    and 'hidden' are not supported.
  - The 'wrap' property supports only 'nowrap' (which is the default) or 'wrap'. The
    rarely-used 'wrap-reverse' is not supported.
  - Rather than allowing arbitrary combinations of flexGrow, flexShrink and
    flexBasis, this algorithm supports only the three most common combinations:
      - flex: 0 is equiavlent to flex: 0 0 auto
      - flex: n (where n is a positive value) is equivalent to flex: n 0 0
      - flex: -1 (or any negative value) is equivalent to flex: 0 1 auto
  - Margins cannot be specified as 'auto'. They must be specified in terms of pixel
    values, and the default value is 0.
  - The 'baseline' value is not supported for alignItems and alignSelf properties.
  - Values of width, maxWidth, minWidth, height, maxHeight and minHeight must be
    specified as pixel values, not as percentages.
  - There is no support for calculation of dimensions based on intrinsic aspect ratios
    (e.g. images).
  - There is no support for forced breaks.
  - It does not support vertical inline directions (top-to-bottom or bottom-to-top text).

And here is how the implementation deviates from the standard (this is also documented in
Layout.js):
  - Section 4.5 of the spec indicates that all flex items have a default minimum
    main size. For text blocks, for example, this is the width of the widest word.
    Calculating the minimum width is expensive, so we forego it and assume a default
    minimum main size of 0.
  - Min/Max sizes in the main axis are not honored when resolving flexible lengths.
  - The spec indicates that the default value for 'flexDirection' is 'row', but
    the algorithm below assumes a default of 'column'.
This commit is contained in:
Adam Comella
2016-04-26 16:35:46 -07:00
parent b0d00ad338
commit f3dd51ab97
36 changed files with 9789 additions and 4157 deletions
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9
TestResult.xml
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@@ -1,9 +0,0 @@
<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!--This file represents the results of running a test suite-->
<test-results name="src/csharp/Facebook.CSSLayout.Tests/bin/Release/Facebook.CSSLayout.Tests.dll" total="0" failures="0" not-run="0" date="2016-04-01" time="11:01:04">
<environment nunit-version="2.4.8.0" clr-version="4.0.30319.17020" os-version="Unix 15.4.0.0" platform="Unix" cwd="/Users/emilsj/css-layout" machine-name="emilsj-pro" user="emilsj" user-domain="emilsj-pro" />
<culture-info current-culture="en-US" current-uiculture="en-US" />
<test-suite name="src/csharp/Facebook.CSSLayout.Tests/bin/Release/Facebook.CSSLayout.Tests.dll" success="True" time="0.001" asserts="0">
<results />
</test-suite>
</test-results>