f3dd51ab97
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'.
90 lines
2.8 KiB
C#
90 lines
2.8 KiB
C#
/**
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* Copyright (c) 2014, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*/
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namespace Facebook.CSSLayout
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{
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/**
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* Where the output of {@link LayoutEngine#layoutNode(CSSNode, float)} will go in the CSSNode.
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*/
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class CSSLayout
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{
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// This value was chosen based on empiracle data. Even the most complicated
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// layouts should not require more than 16 entries to fit within the cache.
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public const int MAX_CACHED_RESULT_COUNT = 16;
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public const int POSITION_LEFT = 0;
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public const int POSITION_TOP = 1;
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public const int POSITION_RIGHT = 2;
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public const int POSITION_BOTTOM = 3;
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public const int DIMENSION_WIDTH = 0;
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public const int DIMENSION_HEIGHT = 1;
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public float[] position = new float[4];
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public float[] dimensions = {
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CSSConstants.Undefined,
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CSSConstants.Undefined
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};
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public CSSDirection direction = CSSDirection.LTR;
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public float flexBasis;
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public int generationCount;
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public CSSDirection? lastParentDirection;
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public int nextCachedMeasurementsIndex;
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public CSSCachedMeasurement[] cachedMeasurements = new CSSCachedMeasurement[MAX_CACHED_RESULT_COUNT];
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public float[] measuredDimensions = {
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CSSConstants.Undefined,
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CSSConstants.Undefined
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};
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public CSSCachedMeasurement cachedLayout = new CSSCachedMeasurement();
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public void resetResult()
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{
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FillArray(position, 0);
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FillArray(dimensions, CSSConstants.Undefined);
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direction = CSSDirection.LTR;
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flexBasis = 0;
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generationCount = 0;
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lastParentDirection = null;
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nextCachedMeasurementsIndex = 0;
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measuredDimensions[DIMENSION_WIDTH] = CSSConstants.Undefined;
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measuredDimensions[DIMENSION_HEIGHT] = CSSConstants.Undefined;
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cachedLayout.widthMeasureMode = null;
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cachedLayout.heightMeasureMode = null;
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}
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public override string ToString()
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{
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return "layout: {" +
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"left: " + position[POSITION_LEFT] + ", " +
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"top: " + position[POSITION_TOP] + ", " +
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"width: " + dimensions[DIMENSION_WIDTH] + ", " +
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"height: " + dimensions[DIMENSION_HEIGHT] + ", " +
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"direction: " + direction +
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"}";
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}
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static void FillArray<T>(T[] array, T value)
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{
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for (var i = 0; i != array.Length; ++i)
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array[i] = value;
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}
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}
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}
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