/** * Copyright (c) 2014-present, Facebook, Inc. * All rights reserved. * * This source code is licensed under the BSD-style license found in the * LICENSE file in the root directory of this source tree. An additional grant * of patent rights can be found in the PATENTS file in the same directory. */ package com.facebook.csslayout; import com.facebook.infer.annotation.Assertions; import static com.facebook.csslayout.CSSLayout.DIMENSION_HEIGHT; import static com.facebook.csslayout.CSSLayout.DIMENSION_WIDTH; import static com.facebook.csslayout.CSSLayout.POSITION_BOTTOM; import static com.facebook.csslayout.CSSLayout.POSITION_LEFT; import static com.facebook.csslayout.CSSLayout.POSITION_RIGHT; import static com.facebook.csslayout.CSSLayout.POSITION_TOP; /** * Calculates layouts based on CSS style. See {@link #layoutNode(CSSNode, float, float)}. */ public class LayoutEngine { private static final int CSS_FLEX_DIRECTION_COLUMN = CSSFlexDirection.COLUMN.ordinal(); private static final int CSS_FLEX_DIRECTION_COLUMN_REVERSE = CSSFlexDirection.COLUMN_REVERSE.ordinal(); private static final int CSS_FLEX_DIRECTION_ROW = CSSFlexDirection.ROW.ordinal(); private static final int CSS_FLEX_DIRECTION_ROW_REVERSE = CSSFlexDirection.ROW_REVERSE.ordinal(); private static final int CSS_POSITION_RELATIVE = CSSPositionType.RELATIVE.ordinal(); private static final int CSS_POSITION_ABSOLUTE = CSSPositionType.ABSOLUTE.ordinal(); private static final int[] leading = { POSITION_TOP, POSITION_BOTTOM, POSITION_LEFT, POSITION_RIGHT, }; private static final int[] trailing = { POSITION_BOTTOM, POSITION_TOP, POSITION_RIGHT, POSITION_LEFT, }; private static final int[] pos = { POSITION_TOP, POSITION_BOTTOM, POSITION_LEFT, POSITION_RIGHT, }; private static final int[] dim = { DIMENSION_HEIGHT, DIMENSION_HEIGHT, DIMENSION_WIDTH, DIMENSION_WIDTH, }; private static final int[] leadingSpacing = { Spacing.TOP, Spacing.BOTTOM, Spacing.START, Spacing.START }; private static final int[] trailingSpacing = { Spacing.BOTTOM, Spacing.TOP, Spacing.END, Spacing.END }; private static boolean isFlexBasisAuto(CSSNode node) { return CSSConstants.isUndefined(node.style.flexBasis); } private static float getFlexGrowFactor(CSSNode node) { return node.style.flexGrow; } private static float getFlexShrinkFactor(CSSNode node) { return node.style.flexShrink; } private static float boundAxisWithinMinAndMax(CSSNode node, int axis, float value) { float min = CSSConstants.UNDEFINED; float max = CSSConstants.UNDEFINED; if (axis == CSS_FLEX_DIRECTION_COLUMN || axis == CSS_FLEX_DIRECTION_COLUMN_REVERSE) { min = node.style.minHeight; max = node.style.maxHeight; } else if (axis == CSS_FLEX_DIRECTION_ROW || axis == CSS_FLEX_DIRECTION_ROW_REVERSE) { min = node.style.minWidth; max = node.style.maxWidth; } float boundValue = value; if (!Float.isNaN(max) && max >= 0.0 && boundValue > max) { boundValue = max; } if (!Float.isNaN(min) && min >= 0.0 && boundValue < min) { boundValue = min; } return boundValue; } private static float boundAxis(CSSNode node, int axis, float value) { float paddingAndBorderAxis = node.style.padding.getWithFallback(leadingSpacing[axis], leading[axis]) + node.style.border.getWithFallback(leadingSpacing[axis], leading[axis]) + node.style.padding.getWithFallback(trailingSpacing[axis], trailing[axis]) + node.style.border.getWithFallback(trailingSpacing[axis], trailing[axis]); return Math.max(boundAxisWithinMinAndMax(node, axis, value), paddingAndBorderAxis); } private static float getRelativePosition(CSSNode node, int axis) { float lead = node.style.position.getWithFallback(leadingSpacing[axis], leading[axis]); if (!Float.isNaN(lead)) { return lead; } float trailingPos = node.style.position.getWithFallback(trailingSpacing[axis], trailing[axis]); return Float.isNaN(trailingPos) ? 0 : -trailingPos; } private static void setPosition(CSSNode node, CSSDirection direction) { int mainAxis = resolveAxis(getFlexDirection(node), direction); int crossAxis = getCrossFlexDirection(mainAxis, direction); node.layout.position[leading[mainAxis]] = node.style.margin.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + getRelativePosition(node, mainAxis); node.layout.position[trailing[mainAxis]] = node.style.margin.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis]) + getRelativePosition(node, mainAxis); node.layout.position[leading[crossAxis]] = node.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + getRelativePosition(node, crossAxis); node.layout.position[trailing[crossAxis]] = node.style.margin.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis]) + getRelativePosition(node, crossAxis); } private static int resolveAxis( int axis, CSSDirection direction) { if (direction == CSSDirection.RTL) { if (axis == CSS_FLEX_DIRECTION_ROW) { return CSS_FLEX_DIRECTION_ROW_REVERSE; } else if (axis == CSS_FLEX_DIRECTION_ROW_REVERSE) { return CSS_FLEX_DIRECTION_ROW; } } return axis; } private static CSSDirection resolveDirection(CSSNode node, CSSDirection parentDirection) { CSSDirection direction = node.style.direction; if (direction == CSSDirection.INHERIT) { direction = (parentDirection == null ? CSSDirection.LTR : parentDirection); } return direction; } private static int getFlexDirection(CSSNode node) { return node.style.flexDirection.ordinal(); } private static int getCrossFlexDirection( int axis, CSSDirection direction) { if (axis == CSS_FLEX_DIRECTION_COLUMN || axis == CSS_FLEX_DIRECTION_COLUMN_REVERSE) { return resolveAxis(CSS_FLEX_DIRECTION_ROW, direction); } else { return CSS_FLEX_DIRECTION_COLUMN; } } private static CSSAlign getAlignItem(CSSNode node, CSSNode child) { if (child.style.alignSelf != CSSAlign.AUTO) { return child.style.alignSelf; } return node.style.alignItems; } private static boolean isMeasureDefined(CSSNode node) { return node.isMeasureDefined(); } /*package*/ static void layoutNode( CSSLayoutContext layoutContext, CSSNode node, float availableWidth, float availableHeight, CSSDirection parentDirection) { // Increment the generation count. This will force the recursive routine to visit // all dirty nodes at least once. Subsequent visits will be skipped if the input // parameters don't change. layoutContext.currentGenerationCount++; CSSMeasureMode widthMeasureMode = CSSMeasureMode.UNDEFINED; CSSMeasureMode heightMeasureMode = CSSMeasureMode.UNDEFINED; if (!Float.isNaN(availableWidth)) { widthMeasureMode = CSSMeasureMode.EXACTLY; } else if (node.style.dimensions[DIMENSION_WIDTH] >= 0.0) { float marginAxisRow = (node.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + node.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); availableWidth = node.style.dimensions[DIMENSION_WIDTH] + marginAxisRow; widthMeasureMode = CSSMeasureMode.EXACTLY; } else if (node.style.maxWidth >= 0.0) { availableWidth = node.style.maxWidth; widthMeasureMode = CSSMeasureMode.AT_MOST; } if (!Float.isNaN(availableHeight)) { heightMeasureMode = CSSMeasureMode.EXACTLY; } else if (node.style.dimensions[DIMENSION_HEIGHT] >= 0.0) { float marginAxisColumn = (node.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + node.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); availableHeight = node.style.dimensions[DIMENSION_HEIGHT] + marginAxisColumn; heightMeasureMode = CSSMeasureMode.EXACTLY; } else if (node.style.maxHeight >= 0.0) { availableHeight = node.style.maxHeight; heightMeasureMode = CSSMeasureMode.AT_MOST; } if (layoutNodeInternal(layoutContext, node, availableWidth, availableHeight, parentDirection, widthMeasureMode, heightMeasureMode, true, "initial")) { setPosition(node, node.layout.direction); } } /*package*/ static boolean canUseCachedMeasurement( boolean isTextNode, float availableWidth, float availableHeight, float marginRow, float marginColumn, CSSMeasureMode widthMeasureMode, CSSMeasureMode heightMeasureMode, CSSCachedMeasurement cachedLayout) { boolean isHeightSame = (cachedLayout.heightMeasureMode == CSSMeasureMode.UNDEFINED && heightMeasureMode == CSSMeasureMode.UNDEFINED) || (cachedLayout.heightMeasureMode == heightMeasureMode && FloatUtil.floatsEqual(cachedLayout.availableHeight, availableHeight)); boolean isWidthSame = (cachedLayout.widthMeasureMode == CSSMeasureMode.UNDEFINED && widthMeasureMode == CSSMeasureMode.UNDEFINED) || (cachedLayout.widthMeasureMode == widthMeasureMode && FloatUtil.floatsEqual(cachedLayout.availableWidth, availableWidth)); if (isHeightSame && isWidthSame) { return true; } boolean isHeightValid = (cachedLayout.heightMeasureMode == CSSMeasureMode.UNDEFINED && heightMeasureMode == CSSMeasureMode.AT_MOST && cachedLayout.computedHeight <= (availableHeight - marginColumn)) || (heightMeasureMode == CSSMeasureMode.EXACTLY && FloatUtil.floatsEqual(cachedLayout.computedHeight, availableHeight - marginColumn)); if (isWidthSame && isHeightValid) { return true; } boolean isWidthValid = (cachedLayout.widthMeasureMode == CSSMeasureMode.UNDEFINED && widthMeasureMode == CSSMeasureMode.AT_MOST && cachedLayout.computedWidth <= (availableWidth - marginRow)) || (widthMeasureMode == CSSMeasureMode.EXACTLY && FloatUtil.floatsEqual(cachedLayout.computedWidth, availableWidth - marginRow)); if (isHeightSame && isWidthValid) { return true; } if (isHeightValid && isWidthValid) { return true; } // We know this to be text so we can apply some more specialized heuristics. if (isTextNode) { if (isWidthSame) { if (heightMeasureMode == CSSMeasureMode.UNDEFINED) { // Width is the same and height is not restricted. Re-use cahced value. return true; } if (heightMeasureMode == CSSMeasureMode.AT_MOST && cachedLayout.computedHeight < (availableHeight - marginColumn)) { // Width is the same and height restriction is greater than the cached height. Re-use cached value. return true; } // Width is the same but height restriction imposes smaller height than previously measured. // Update the cached value to respect the new height restriction. cachedLayout.computedHeight = availableHeight - marginColumn; return true; } if (cachedLayout.widthMeasureMode == CSSMeasureMode.UNDEFINED) { if (widthMeasureMode == CSSMeasureMode.UNDEFINED || (widthMeasureMode == CSSMeasureMode.AT_MOST && cachedLayout.computedWidth <= (availableWidth - marginRow))) { // Previsouly this text was measured with no width restriction, if width is now restricted // but to a larger value than the previsouly measured width we can re-use the measurement // as we know it will fit. return true; } } } return false; } // // This is a wrapper around the layoutNodeImpl function. It determines // whether the layout request is redundant and can be skipped. // // Parameters: // Input parameters are the same as layoutNodeImpl (see below) // Return parameter is true if layout was performed, false if skipped // private static boolean layoutNodeInternal( CSSLayoutContext layoutContext, CSSNode node, float availableWidth, float availableHeight, CSSDirection parentDirection, CSSMeasureMode widthMeasureMode, CSSMeasureMode heightMeasureMode, boolean performLayout, String reason) { CSSLayout layout = node.layout; boolean needToVisitNode = (node.isDirty() && layout.generationCount != layoutContext.currentGenerationCount) || layout.lastParentDirection != parentDirection; if (needToVisitNode) { // Invalidate the cached results. layout.nextCachedMeasurementsIndex = 0; layout.cachedLayout.widthMeasureMode = null; layout.cachedLayout.heightMeasureMode = null; } CSSCachedMeasurement cachedResults = null; // Determine whether the results are already cached. We maintain a separate // cache for layouts and measurements. A layout operation modifies the positions // and dimensions for nodes in the subtree. The algorithm assumes that each node // gets layed out a maximum of one time per tree layout, but multiple measurements // may be required to resolve all of the flex dimensions. // We handle nodes with measure functions specially here because they are the most // expensive to measure, so it's worth avoiding redundant measurements if at all possible. if (isMeasureDefined(node)) { float marginAxisRow = node.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + node.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW]); float marginAxisColumn = node.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + node.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN]); // First, try to use the layout cache. if (canUseCachedMeasurement(node.isTextNode(), availableWidth, availableHeight, marginAxisRow, marginAxisColumn, widthMeasureMode, heightMeasureMode, layout.cachedLayout)) { cachedResults = layout.cachedLayout; } else { // Try to use the measurement cache. for (int i = 0; i < layout.nextCachedMeasurementsIndex; i++) { if (canUseCachedMeasurement(node.isTextNode(), availableWidth, availableHeight, marginAxisRow, marginAxisColumn, widthMeasureMode, heightMeasureMode, layout.cachedMeasurements[i])) { cachedResults = layout.cachedMeasurements[i]; break; } } } } else if (performLayout) { if (FloatUtil.floatsEqual(layout.cachedLayout.availableWidth, availableWidth) && FloatUtil.floatsEqual(layout.cachedLayout.availableHeight, availableHeight) && layout.cachedLayout.widthMeasureMode == widthMeasureMode && layout.cachedLayout.heightMeasureMode == heightMeasureMode) { cachedResults = layout.cachedLayout; } } else { for (int i = 0; i < layout.nextCachedMeasurementsIndex; i++) { if (FloatUtil.floatsEqual(layout.cachedMeasurements[i].availableWidth, availableWidth) && FloatUtil.floatsEqual(layout.cachedMeasurements[i].availableHeight, availableHeight) && layout.cachedMeasurements[i].widthMeasureMode == widthMeasureMode && layout.cachedMeasurements[i].heightMeasureMode == heightMeasureMode) { cachedResults = layout.cachedMeasurements[i]; break; } } } if (!needToVisitNode && cachedResults != null) { layout.measuredDimensions[DIMENSION_WIDTH] = cachedResults.computedWidth; layout.measuredDimensions[DIMENSION_HEIGHT] = cachedResults.computedHeight; } else { layoutNodeImpl(layoutContext, node, availableWidth, availableHeight, parentDirection, widthMeasureMode, heightMeasureMode, performLayout); layout.lastParentDirection = parentDirection; if (cachedResults == null) { if (layout.nextCachedMeasurementsIndex == CSSLayout.MAX_CACHED_RESULT_COUNT) { layout.nextCachedMeasurementsIndex = 0; } CSSCachedMeasurement newCacheEntry = null; if (performLayout) { // Use the single layout cache entry. newCacheEntry = layout.cachedLayout; } else { // Allocate a new measurement cache entry. newCacheEntry = layout.cachedMeasurements[layout.nextCachedMeasurementsIndex]; if (newCacheEntry == null) { newCacheEntry = new CSSCachedMeasurement(); layout.cachedMeasurements[layout.nextCachedMeasurementsIndex] = newCacheEntry; } layout.nextCachedMeasurementsIndex++; } newCacheEntry.availableWidth = availableWidth; newCacheEntry.availableHeight = availableHeight; newCacheEntry.widthMeasureMode = widthMeasureMode; newCacheEntry.heightMeasureMode = heightMeasureMode; newCacheEntry.computedWidth = layout.measuredDimensions[DIMENSION_WIDTH]; newCacheEntry.computedHeight = layout.measuredDimensions[DIMENSION_HEIGHT]; } } if (performLayout) { node.layout.dimensions[DIMENSION_WIDTH] = node.layout.measuredDimensions[DIMENSION_WIDTH]; node.layout.dimensions[DIMENSION_HEIGHT] = node.layout.measuredDimensions[DIMENSION_HEIGHT]; node.markHasNewLayout(); } layout.generationCount = layoutContext.currentGenerationCount; return (needToVisitNode || cachedResults == null); } // // This is the main routine that implements a subset of the flexbox layout algorithm // described in the W3C CSS documentation: https://www.w3.org/TR/css3-flexbox/. // // Limitations of this algorithm, compared to the full standard: // * 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 1 auto // If POSITIVE_FLEX_IS_AUTO is 0, then it is equivalent to flex: n 0 0 // This is faster because the content doesn't need to be measured, but it's // less flexible because the basis is always 0 and can't be overriden with // the width/height attributes. // 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). // // Deviations from standard: // * 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'. // // Input parameters: // - node: current node to be sized and layed out // - availableWidth & availableHeight: available size to be used for sizing the node // or CSS_UNDEFINED if the size is not available; interpretation depends on layout // flags // - parentDirection: the inline (text) direction within the parent (left-to-right or // right-to-left) // - widthMeasureMode: indicates the sizing rules for the width (see below for explanation) // - heightMeasureMode: indicates the sizing rules for the height (see below for explanation) // - performLayout: specifies whether the caller is interested in just the dimensions // of the node or it requires the entire node and its subtree to be layed out // (with final positions) // // Details: // This routine is called recursively to lay out subtrees of flexbox elements. It uses the // information in node.style, which is treated as a read-only input. It is responsible for // setting the layout.direction and layout.measured_dimensions fields for the input node as well // as the layout.position and layout.line_index fields for its child nodes. The // layout.measured_dimensions field includes any border or padding for the node but does // not include margins. // // The spec describes four different layout modes: "fill available", "max content", "min content", // and "fit content". Of these, we don't use "min content" because we don't support default // minimum main sizes (see above for details). Each of our measure modes maps to a layout mode // from the spec (https://www.w3.org/TR/css3-sizing/#terms): // - CSS_MEASURE_MODE_UNDEFINED: max content // - CSS_MEASURE_MODE_EXACTLY: fill available // - CSS_MEASURE_MODE_AT_MOST: fit content // // When calling layoutNodeImpl and layoutNodeInternal, if the caller passes an available size of // undefined then it must also pass a measure mode of CSS_MEASURE_MODE_UNDEFINED in that dimension. // private static void layoutNodeImpl( CSSLayoutContext layoutContext, CSSNode node, float availableWidth, float availableHeight, CSSDirection parentDirection, CSSMeasureMode widthMeasureMode, CSSMeasureMode heightMeasureMode, boolean performLayout) { Assertions.assertCondition(Float.isNaN(availableWidth) ? widthMeasureMode == CSSMeasureMode.UNDEFINED : true, "availableWidth is indefinite so widthMeasureMode must be CSSMeasureMode.UNDEFINED"); Assertions.assertCondition(Float.isNaN(availableHeight) ? heightMeasureMode == CSSMeasureMode.UNDEFINED : true, "availableHeight is indefinite so heightMeasureMode must be CSSMeasureMode.UNDEFINED"); float paddingAndBorderAxisRow = ((node.style.padding.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + node.style.border.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW])) + (node.style.padding.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW]) + node.style.border.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW]))); float paddingAndBorderAxisColumn = ((node.style.padding.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + node.style.border.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN])) + (node.style.padding.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN]) + node.style.border.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN]))); float marginAxisRow = (node.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + node.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); float marginAxisColumn = (node.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + node.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); // Set the resolved resolution in the node's layout. CSSDirection direction = resolveDirection(node, parentDirection); node.layout.direction = direction; // For content (text) nodes, determine the dimensions based on the text contents. if (isMeasureDefined(node)) { float innerWidth = availableWidth - marginAxisRow - paddingAndBorderAxisRow; float innerHeight = availableHeight - marginAxisColumn - paddingAndBorderAxisColumn; if (widthMeasureMode == CSSMeasureMode.EXACTLY && heightMeasureMode == CSSMeasureMode.EXACTLY) { // Don't bother sizing the text if both dimensions are already defined. node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, availableWidth - marginAxisRow); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, availableHeight - marginAxisColumn); } else if (innerWidth <= 0 || innerHeight <= 0) { // Don't bother sizing the text if there's no horizontal or vertical space. node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, 0); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, 0); } else { // Measure the text under the current constraints. MeasureOutput measureDim = node.measure( layoutContext.measureOutput, innerWidth, widthMeasureMode, innerHeight, heightMeasureMode ); node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, (widthMeasureMode == CSSMeasureMode.UNDEFINED || widthMeasureMode == CSSMeasureMode.AT_MOST) ? measureDim.width + paddingAndBorderAxisRow : availableWidth - marginAxisRow); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, (heightMeasureMode == CSSMeasureMode.UNDEFINED || heightMeasureMode == CSSMeasureMode.AT_MOST) ? measureDim.height + paddingAndBorderAxisColumn : availableHeight - marginAxisColumn); } return; } // For nodes with no children, use the available values if they were provided, or // the minimum size as indicated by the padding and border sizes. int childCount = node.getChildCount(); if (childCount == 0) { node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, (widthMeasureMode == CSSMeasureMode.UNDEFINED || widthMeasureMode == CSSMeasureMode.AT_MOST) ? paddingAndBorderAxisRow : availableWidth - marginAxisRow); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, (heightMeasureMode == CSSMeasureMode.UNDEFINED || heightMeasureMode == CSSMeasureMode.AT_MOST) ? paddingAndBorderAxisColumn : availableHeight - marginAxisColumn); return; } // If we're not being asked to perform a full layout, we can handle a number of common // cases here without incurring the cost of the remaining function. if (!performLayout) { // If we're being asked to size the content with an at most constraint but there is no available width, // the measurement will always be zero. if (widthMeasureMode == CSSMeasureMode.AT_MOST && availableWidth <= 0 && heightMeasureMode == CSSMeasureMode.AT_MOST && availableHeight <= 0) { node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, 0); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, 0); return; } if (widthMeasureMode == CSSMeasureMode.AT_MOST && availableWidth <= 0) { node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, 0); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, Float.isNaN(availableHeight) ? 0 : (availableHeight - marginAxisColumn)); return; } if (heightMeasureMode == CSSMeasureMode.AT_MOST && availableHeight <= 0) { node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, Float.isNaN(availableWidth) ? 0 : (availableWidth - marginAxisRow)); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, 0); return; } // If we're being asked to use an exact width/height, there's no need to measure the children. if (widthMeasureMode == CSSMeasureMode.EXACTLY && heightMeasureMode == CSSMeasureMode.EXACTLY) { node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, availableWidth - marginAxisRow); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, availableHeight - marginAxisColumn); return; } } // STEP 1: CALCULATE VALUES FOR REMAINDER OF ALGORITHM int mainAxis = resolveAxis(getFlexDirection(node), direction); int crossAxis = getCrossFlexDirection(mainAxis, direction); boolean isMainAxisRow = (mainAxis == CSS_FLEX_DIRECTION_ROW || mainAxis == CSS_FLEX_DIRECTION_ROW_REVERSE); CSSJustify justifyContent = node.style.justifyContent; boolean isNodeFlexWrap = (node.style.flexWrap == CSSWrap.WRAP); CSSNode firstAbsoluteChild = null; CSSNode currentAbsoluteChild = null; float leadingPaddingAndBorderMain = (node.style.padding.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + node.style.border.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis])); float trailingPaddingAndBorderMain = (node.style.padding.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis]) + node.style.border.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])); float leadingPaddingAndBorderCross = (node.style.padding.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + node.style.border.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis])); float paddingAndBorderAxisMain = ((node.style.padding.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + node.style.border.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis])) + (node.style.padding.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis]) + node.style.border.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis]))); float paddingAndBorderAxisCross = ((node.style.padding.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + node.style.border.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis])) + (node.style.padding.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis]) + node.style.border.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis]))); CSSMeasureMode measureModeMainDim = isMainAxisRow ? widthMeasureMode : heightMeasureMode; CSSMeasureMode measureModeCrossDim = isMainAxisRow ? heightMeasureMode : widthMeasureMode; // STEP 2: DETERMINE AVAILABLE SIZE IN MAIN AND CROSS DIRECTIONS float availableInnerWidth = availableWidth - marginAxisRow - paddingAndBorderAxisRow; float availableInnerHeight = availableHeight - marginAxisColumn - paddingAndBorderAxisColumn; float availableInnerMainDim = isMainAxisRow ? availableInnerWidth : availableInnerHeight; float availableInnerCrossDim = isMainAxisRow ? availableInnerHeight : availableInnerWidth; // STEP 3: DETERMINE FLEX BASIS FOR EACH ITEM CSSNode child; int i; float childWidth; float childHeight; CSSMeasureMode childWidthMeasureMode; CSSMeasureMode childHeightMeasureMode; for (i = 0; i < childCount; i++) { child = node.getChildAt(i); if (performLayout) { // Set the initial position (relative to the parent). CSSDirection childDirection = resolveDirection(child, direction); setPosition(child, childDirection); } // Absolute-positioned children don't participate in flex layout. Add them // to a list that we can process later. if (child.style.positionType == CSSPositionType.ABSOLUTE) { // Store a private linked list of absolutely positioned children // so that we can efficiently traverse them later. if (firstAbsoluteChild == null) { firstAbsoluteChild = child; } if (currentAbsoluteChild != null) { currentAbsoluteChild.nextChild = child; } currentAbsoluteChild = child; child.nextChild = null; } else { if (isMainAxisRow && (child.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0)) { // The width is definite, so use that as the flex basis. child.layout.computedFlexBasis = Math.max(child.style.dimensions[DIMENSION_WIDTH], ((child.style.padding.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + child.style.border.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW])) + (child.style.padding.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW]) + child.style.border.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])))); } else if (!isMainAxisRow && (child.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0)) { // The height is definite, so use that as the flex basis. child.layout.computedFlexBasis = Math.max(child.style.dimensions[DIMENSION_HEIGHT], ((child.style.padding.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + child.style.border.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN])) + (child.style.padding.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN]) + child.style.border.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])))); } else if (!isFlexBasisAuto(child) && !Float.isNaN(availableInnerMainDim)) { if (Float.isNaN(child.layout.computedFlexBasis)) { child.layout.computedFlexBasis = Math.max(child.style.flexBasis, ((child.style.padding.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + child.style.border.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis])) + (child.style.padding.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis]) + child.style.border.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])))); } } else { // Compute the flex basis and hypothetical main size (i.e. the clamped flex basis). childWidth = CSSConstants.UNDEFINED; childHeight = CSSConstants.UNDEFINED; childWidthMeasureMode = CSSMeasureMode.UNDEFINED; childHeightMeasureMode = CSSMeasureMode.UNDEFINED; if ((child.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0)) { childWidth = child.style.dimensions[DIMENSION_WIDTH] + (child.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + child.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); childWidthMeasureMode = CSSMeasureMode.EXACTLY; } if ((child.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0)) { childHeight = child.style.dimensions[DIMENSION_HEIGHT] + (child.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + child.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); childHeightMeasureMode = CSSMeasureMode.EXACTLY; } // The W3C spec doesn't say anything about the 'overflow' property, // but all major browsers appear to implement the following logic. if ((!isMainAxisRow && node.style.overflow == CSSOverflow.SCROLL) || node.style.overflow != CSSOverflow.SCROLL) { if (Float.isNaN(childWidth) && !Float.isNaN(availableInnerWidth)) { childWidth = availableInnerWidth; childWidthMeasureMode = CSSMeasureMode.AT_MOST; } } if ((isMainAxisRow && node.style.overflow == CSSOverflow.SCROLL) || node.style.overflow != CSSOverflow.SCROLL) { if (Float.isNaN(childHeight) && !Float.isNaN(availableInnerHeight)) { childHeight = availableInnerHeight; childHeightMeasureMode = CSSMeasureMode.AT_MOST; } } // If child has no defined size in the cross axis and is set to stretch, set the cross // axis to be measured exactly with the available inner width if (!isMainAxisRow && !Float.isNaN(availableInnerWidth) && !(child.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0) && widthMeasureMode == CSSMeasureMode.EXACTLY && getAlignItem(node, child) == CSSAlign.STRETCH) { childWidth = availableInnerWidth; childWidthMeasureMode = CSSMeasureMode.EXACTLY; } if (isMainAxisRow && !Float.isNaN(availableInnerHeight) && !(child.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0) && heightMeasureMode == CSSMeasureMode.EXACTLY && getAlignItem(node, child) == CSSAlign.STRETCH) { childHeight = availableInnerHeight; childHeightMeasureMode = CSSMeasureMode.EXACTLY; } // Measure the child layoutNodeInternal(layoutContext, child, childWidth, childHeight, direction, childWidthMeasureMode, childHeightMeasureMode, false, "measure"); child.layout.computedFlexBasis = Math.max(isMainAxisRow ? child.layout.measuredDimensions[DIMENSION_WIDTH] : child.layout.measuredDimensions[DIMENSION_HEIGHT], ((child.style.padding.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + child.style.border.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis])) + (child.style.padding.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis]) + child.style.border.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])))); } } } // STEP 4: COLLECT FLEX ITEMS INTO FLEX LINES // Indexes of children that represent the first and last items in the line. int startOfLineIndex = 0; int endOfLineIndex = 0; // Number of lines. int lineCount = 0; // Accumulated cross dimensions of all lines so far. float totalLineCrossDim = 0; // Max main dimension of all the lines. float maxLineMainDim = 0; while (endOfLineIndex < childCount) { // Number of items on the currently line. May be different than the difference // between start and end indicates because we skip over absolute-positioned items. int itemsOnLine = 0; // sizeConsumedOnCurrentLine is accumulation of the dimensions and margin // of all the children on the current line. This will be used in order to // either set the dimensions of the node if none already exist or to compute // the remaining space left for the flexible children. float sizeConsumedOnCurrentLine = 0; float totalFlexGrowFactors = 0; float totalFlexShrinkScaledFactors = 0; i = startOfLineIndex; // Maintain a linked list of the child nodes that can shrink and/or grow. CSSNode firstRelativeChild = null; CSSNode currentRelativeChild = null; // Add items to the current line until it's full or we run out of items. while (i < childCount) { child = node.getChildAt(i); child.lineIndex = lineCount; if (child.style.positionType != CSSPositionType.ABSOLUTE) { float outerFlexBasis = child.layout.computedFlexBasis + (child.style.margin.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + child.style.margin.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])); // If this is a multi-line flow and this item pushes us over the available size, we've // hit the end of the current line. Break out of the loop and lay out the current line. if (sizeConsumedOnCurrentLine + outerFlexBasis > availableInnerMainDim && isNodeFlexWrap && itemsOnLine > 0) { break; } sizeConsumedOnCurrentLine += outerFlexBasis; itemsOnLine++; if ((child.style.positionType == CSSPositionType.RELATIVE && (child.style.flexGrow != 0 || child.style.flexShrink != 0))) { totalFlexGrowFactors += getFlexGrowFactor(child); // Unlike the grow factor, the shrink factor is scaled relative to the child // dimension. totalFlexShrinkScaledFactors += getFlexShrinkFactor(child) * child.layout.computedFlexBasis; } // Store a private linked list of children that need to be layed out. if (firstRelativeChild == null) { firstRelativeChild = child; } if (currentRelativeChild != null) { currentRelativeChild.nextChild = child; } currentRelativeChild = child; child.nextChild = null; } i++; endOfLineIndex++; } // If we don't need to measure the cross axis, we can skip the entire flex step. boolean canSkipFlex = !performLayout && measureModeCrossDim == CSSMeasureMode.EXACTLY; // In order to position the elements in the main axis, we have two // controls. The space between the beginning and the first element // and the space between each two elements. float leadingMainDim = 0; float betweenMainDim = 0; // STEP 5: RESOLVING FLEXIBLE LENGTHS ON MAIN AXIS // Calculate the remaining available space that needs to be allocated. // If the main dimension size isn't known, it is computed based on // the line length, so there's no more space left to distribute. float remainingFreeSpace = 0; if (!Float.isNaN(availableInnerMainDim)) { remainingFreeSpace = availableInnerMainDim - sizeConsumedOnCurrentLine; } else if (sizeConsumedOnCurrentLine < 0) { // availableInnerMainDim is indefinite which means the node is being sized based on its content. // sizeConsumedOnCurrentLine is negative which means the node will allocate 0 pixels for // its content. Consequently, remainingFreeSpace is 0 - sizeConsumedOnCurrentLine. remainingFreeSpace = -sizeConsumedOnCurrentLine; } float originalRemainingFreeSpace = remainingFreeSpace; float deltaFreeSpace = 0; if (!canSkipFlex) { float childFlexBasis; float flexShrinkScaledFactor; float flexGrowFactor; float baseMainSize; float boundMainSize; // Do two passes over the flex items to figure out how to distribute the remaining space. // The first pass finds the items whose min/max constraints trigger, freezes them at those // sizes, and excludes those sizes from the remaining space. The second pass sets the size // of each flexible item. It distributes the remaining space amongst the items whose min/max // constraints didn't trigger in pass 1. For the other items, it sets their sizes by forcing // their min/max constraints to trigger again. // // This two pass approach for resolving min/max constraints deviates from the spec. The // spec (https://www.w3.org/TR/css-flexbox-1/#resolve-flexible-lengths) describes a process // that needs to be repeated a variable number of times. The algorithm implemented here // won't handle all cases but it was simpler to implement and it mitigates performance // concerns because we know exactly how many passes it'll do. // First pass: detect the flex items whose min/max constraints trigger float deltaFlexShrinkScaledFactors = 0; float deltaFlexGrowFactors = 0; currentRelativeChild = firstRelativeChild; while (currentRelativeChild != null) { childFlexBasis = currentRelativeChild.layout.computedFlexBasis; if (remainingFreeSpace < 0) { flexShrinkScaledFactor = getFlexShrinkFactor(currentRelativeChild) * childFlexBasis; // Is this child able to shrink? if (flexShrinkScaledFactor != 0) { baseMainSize = childFlexBasis + remainingFreeSpace / totalFlexShrinkScaledFactors * flexShrinkScaledFactor; boundMainSize = boundAxis(currentRelativeChild, mainAxis, baseMainSize); if (baseMainSize != boundMainSize) { // By excluding this item's size and flex factor from remaining, this item's // min/max constraints should also trigger in the second pass resulting in the // item's size calculation being identical in the first and second passes. deltaFreeSpace -= boundMainSize - childFlexBasis; deltaFlexShrinkScaledFactors -= flexShrinkScaledFactor; } } } else if (remainingFreeSpace > 0) { flexGrowFactor = getFlexGrowFactor(currentRelativeChild); // Is this child able to grow? if (flexGrowFactor != 0) { baseMainSize = childFlexBasis + remainingFreeSpace / totalFlexGrowFactors * flexGrowFactor; boundMainSize = boundAxis(currentRelativeChild, mainAxis, baseMainSize); if (baseMainSize != boundMainSize) { // By excluding this item's size and flex factor from remaining, this item's // min/max constraints should also trigger in the second pass resulting in the // item's size calculation being identical in the first and second passes. deltaFreeSpace -= boundMainSize - childFlexBasis; deltaFlexGrowFactors -= flexGrowFactor; } } } currentRelativeChild = currentRelativeChild.nextChild; } totalFlexShrinkScaledFactors += deltaFlexShrinkScaledFactors; totalFlexGrowFactors += deltaFlexGrowFactors; remainingFreeSpace += deltaFreeSpace; // Second pass: resolve the sizes of the flexible items deltaFreeSpace = 0; currentRelativeChild = firstRelativeChild; while (currentRelativeChild != null) { childFlexBasis = currentRelativeChild.layout.computedFlexBasis; float updatedMainSize = childFlexBasis; if (remainingFreeSpace < 0) { flexShrinkScaledFactor = getFlexShrinkFactor(currentRelativeChild) * childFlexBasis; // Is this child able to shrink? if (flexShrinkScaledFactor != 0) { updatedMainSize = boundAxis(currentRelativeChild, mainAxis, childFlexBasis + remainingFreeSpace / totalFlexShrinkScaledFactors * flexShrinkScaledFactor); } } else if (remainingFreeSpace > 0) { flexGrowFactor = getFlexGrowFactor(currentRelativeChild); // Is this child able to grow? if (flexGrowFactor != 0) { updatedMainSize = boundAxis(currentRelativeChild, mainAxis, childFlexBasis + remainingFreeSpace / totalFlexGrowFactors * flexGrowFactor); } } deltaFreeSpace -= updatedMainSize - childFlexBasis; if (isMainAxisRow) { childWidth = updatedMainSize + (currentRelativeChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + currentRelativeChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); childWidthMeasureMode = CSSMeasureMode.EXACTLY; if (!Float.isNaN(availableInnerCrossDim) && !(currentRelativeChild.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0) && heightMeasureMode == CSSMeasureMode.EXACTLY && getAlignItem(node, currentRelativeChild) == CSSAlign.STRETCH) { childHeight = availableInnerCrossDim; childHeightMeasureMode = CSSMeasureMode.EXACTLY; } else if (!(currentRelativeChild.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0)) { childHeight = availableInnerCrossDim; childHeightMeasureMode = Float.isNaN(childHeight) ? CSSMeasureMode.UNDEFINED : CSSMeasureMode.AT_MOST; } else { childHeight = currentRelativeChild.style.dimensions[DIMENSION_HEIGHT] + (currentRelativeChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + currentRelativeChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); childHeightMeasureMode = CSSMeasureMode.EXACTLY; } } else { childHeight = updatedMainSize + (currentRelativeChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + currentRelativeChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); childHeightMeasureMode = CSSMeasureMode.EXACTLY; if (!Float.isNaN(availableInnerCrossDim) && !(currentRelativeChild.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0) && widthMeasureMode == CSSMeasureMode.EXACTLY && getAlignItem(node, currentRelativeChild) == CSSAlign.STRETCH) { childWidth = availableInnerCrossDim; childWidthMeasureMode = CSSMeasureMode.EXACTLY; } else if (!(currentRelativeChild.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0)) { childWidth = availableInnerCrossDim; childWidthMeasureMode = Float.isNaN(childWidth) ? CSSMeasureMode.UNDEFINED : CSSMeasureMode.AT_MOST; } else { childWidth = currentRelativeChild.style.dimensions[DIMENSION_WIDTH] + (currentRelativeChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + currentRelativeChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); childWidthMeasureMode = CSSMeasureMode.EXACTLY; } } boolean requiresStretchLayout = !(currentRelativeChild.style.dimensions[dim[crossAxis]] >= 0.0) && getAlignItem(node, currentRelativeChild) == CSSAlign.STRETCH; // Recursively call the layout algorithm for this child with the updated main size. layoutNodeInternal(layoutContext, currentRelativeChild, childWidth, childHeight, direction, childWidthMeasureMode, childHeightMeasureMode, performLayout && !requiresStretchLayout, "flex"); currentRelativeChild = currentRelativeChild.nextChild; } } remainingFreeSpace = originalRemainingFreeSpace + deltaFreeSpace; // STEP 6: MAIN-AXIS JUSTIFICATION & CROSS-AXIS SIZE DETERMINATION // At this point, all the children have their dimensions set in the main axis. // Their dimensions are also set in the cross axis with the exception of items // that are aligned "stretch". We need to compute these stretch values and // set the final positions. // If we are using "at most" rules in the main axis, we won't distribute // any remaining space at this point. if (measureModeMainDim == CSSMeasureMode.AT_MOST) { remainingFreeSpace = 0; } // Use justifyContent to figure out how to allocate the remaining space // available in the main axis. if (justifyContent != CSSJustify.FLEX_START) { if (justifyContent == CSSJustify.CENTER) { leadingMainDim = remainingFreeSpace / 2; } else if (justifyContent == CSSJustify.FLEX_END) { leadingMainDim = remainingFreeSpace; } else if (justifyContent == CSSJustify.SPACE_BETWEEN) { remainingFreeSpace = Math.max(remainingFreeSpace, 0); if (itemsOnLine > 1) { betweenMainDim = remainingFreeSpace / (itemsOnLine - 1); } else { betweenMainDim = 0; } } else if (justifyContent == CSSJustify.SPACE_AROUND) { // Space on the edges is half of the space between elements betweenMainDim = remainingFreeSpace / itemsOnLine; leadingMainDim = betweenMainDim / 2; } } float mainDim = leadingPaddingAndBorderMain + leadingMainDim; float crossDim = 0; for (i = startOfLineIndex; i < endOfLineIndex; ++i) { child = node.getChildAt(i); if (child.style.positionType == CSSPositionType.ABSOLUTE && !Float.isNaN(child.style.position.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]))) { if (performLayout) { // In case the child is position absolute and has left/top being // defined, we override the position to whatever the user said // (and margin/border). child.layout.position[pos[mainAxis]] = (Float.isNaN(child.style.position.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis])) ? 0 : child.style.position.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis])) + node.style.border.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + child.style.margin.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]); } } else { if (performLayout) { // If the child is position absolute (without top/left) or relative, // we put it at the current accumulated offset. child.layout.position[pos[mainAxis]] += mainDim; } // Now that we placed the element, we need to update the variables. // We need to do that only for relative elements. Absolute elements // do not take part in that phase. if (child.style.positionType == CSSPositionType.RELATIVE) { if (canSkipFlex) { // If we skipped the flex step, then we can't rely on the measuredDims because // they weren't computed. This means we can't call getDimWithMargin. mainDim += betweenMainDim + (child.style.margin.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + child.style.margin.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])) + child.layout.computedFlexBasis; crossDim = availableInnerCrossDim; } else { // The main dimension is the sum of all the elements dimension plus // the spacing. mainDim += betweenMainDim + (child.layout.measuredDimensions[dim[mainAxis]] + child.style.margin.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]) + child.style.margin.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])); // The cross dimension is the max of the elements dimension since there // can only be one element in that cross dimension. crossDim = Math.max(crossDim, (child.layout.measuredDimensions[dim[crossAxis]] + child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + child.style.margin.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis]))); } } } } mainDim += trailingPaddingAndBorderMain; float containerCrossAxis = availableInnerCrossDim; if (measureModeCrossDim == CSSMeasureMode.UNDEFINED || measureModeCrossDim == CSSMeasureMode.AT_MOST) { // Compute the cross axis from the max cross dimension of the children. containerCrossAxis = boundAxis(node, crossAxis, crossDim + paddingAndBorderAxisCross) - paddingAndBorderAxisCross; if (measureModeCrossDim == CSSMeasureMode.AT_MOST) { containerCrossAxis = Math.min(containerCrossAxis, availableInnerCrossDim); } } // If there's no flex wrap, the cross dimension is defined by the container. if (!isNodeFlexWrap && measureModeCrossDim == CSSMeasureMode.EXACTLY) { crossDim = availableInnerCrossDim; } // Clamp to the min/max size specified on the container. crossDim = boundAxis(node, crossAxis, crossDim + paddingAndBorderAxisCross) - paddingAndBorderAxisCross; // STEP 7: CROSS-AXIS ALIGNMENT // We can skip child alignment if we're just measuring the container. if (performLayout) { for (i = startOfLineIndex; i < endOfLineIndex; ++i) { child = node.getChildAt(i); if (child.style.positionType == CSSPositionType.ABSOLUTE) { // If the child is absolutely positioned and has a top/left/bottom/right // set, override all the previously computed positions to set it correctly. if (!Float.isNaN(child.style.position.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]))) { child.layout.position[pos[crossAxis]] = (Float.isNaN(child.style.position.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis])) ? 0 : child.style.position.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis])) + node.style.border.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]); } else { child.layout.position[pos[crossAxis]] = leadingPaddingAndBorderCross + child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]); } } else { float leadingCrossDim = leadingPaddingAndBorderCross; // For a relative children, we're either using alignItems (parent) or // alignSelf (child) in order to determine the position in the cross axis CSSAlign alignItem = getAlignItem(node, child); // If the child uses align stretch, we need to lay it out one more time, this time // forcing the cross-axis size to be the computed cross size for the current line. if (alignItem == CSSAlign.STRETCH) { childWidth = child.layout.measuredDimensions[DIMENSION_WIDTH] + (child.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + child.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); childHeight = child.layout.measuredDimensions[DIMENSION_HEIGHT] + (child.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + child.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); boolean isCrossSizeDefinite = false; if (isMainAxisRow) { isCrossSizeDefinite = (child.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0); childHeight = crossDim; } else { isCrossSizeDefinite = (child.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0); childWidth = crossDim; } // If the child defines a definite size for its cross axis, there's no need to stretch. if (!isCrossSizeDefinite) { childWidthMeasureMode = Float.isNaN(childWidth) ? CSSMeasureMode.UNDEFINED : CSSMeasureMode.EXACTLY; childHeightMeasureMode = Float.isNaN(childHeight) ? CSSMeasureMode.UNDEFINED : CSSMeasureMode.EXACTLY; layoutNodeInternal(layoutContext, child, childWidth, childHeight, direction, childWidthMeasureMode, childHeightMeasureMode, true, "stretch"); } } else if (alignItem != CSSAlign.FLEX_START) { float remainingCrossDim = containerCrossAxis - (child.layout.measuredDimensions[dim[crossAxis]] + child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + child.style.margin.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis])); if (alignItem == CSSAlign.CENTER) { leadingCrossDim += remainingCrossDim / 2; } else { // CSSAlign.FLEX_END leadingCrossDim += remainingCrossDim; } } // And we apply the position child.layout.position[pos[crossAxis]] += totalLineCrossDim + leadingCrossDim; } } } totalLineCrossDim += crossDim; maxLineMainDim = Math.max(maxLineMainDim, mainDim); // Reset variables for new line. lineCount++; startOfLineIndex = endOfLineIndex; endOfLineIndex = startOfLineIndex; } // STEP 8: MULTI-LINE CONTENT ALIGNMENT if (lineCount > 1 && performLayout && !Float.isNaN(availableInnerCrossDim)) { float remainingAlignContentDim = availableInnerCrossDim - totalLineCrossDim; float crossDimLead = 0; float currentLead = leadingPaddingAndBorderCross; CSSAlign alignContent = node.style.alignContent; if (alignContent == CSSAlign.FLEX_END) { currentLead += remainingAlignContentDim; } else if (alignContent == CSSAlign.CENTER) { currentLead += remainingAlignContentDim / 2; } else if (alignContent == CSSAlign.STRETCH) { if (availableInnerCrossDim > totalLineCrossDim) { crossDimLead = (remainingAlignContentDim / lineCount); } } int endIndex = 0; for (i = 0; i < lineCount; ++i) { int startIndex = endIndex; int j; // compute the line's height and find the endIndex float lineHeight = 0; for (j = startIndex; j < childCount; ++j) { child = node.getChildAt(j); if (child.style.positionType != CSSPositionType.RELATIVE) { continue; } if (child.lineIndex != i) { break; } if ((child.layout.measuredDimensions[dim[crossAxis]] >= 0.0)) { lineHeight = Math.max(lineHeight, child.layout.measuredDimensions[dim[crossAxis]] + (child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]) + child.style.margin.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis]))); } } endIndex = j; lineHeight += crossDimLead; if (performLayout) { for (j = startIndex; j < endIndex; ++j) { child = node.getChildAt(j); if (child.style.positionType != CSSPositionType.RELATIVE) { continue; } CSSAlign alignContentAlignItem = getAlignItem(node, child); if (alignContentAlignItem == CSSAlign.FLEX_START) { child.layout.position[pos[crossAxis]] = currentLead + child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]); } else if (alignContentAlignItem == CSSAlign.FLEX_END) { child.layout.position[pos[crossAxis]] = currentLead + lineHeight - child.style.margin.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis]) - child.layout.measuredDimensions[dim[crossAxis]]; } else if (alignContentAlignItem == CSSAlign.CENTER) { childHeight = child.layout.measuredDimensions[dim[crossAxis]]; child.layout.position[pos[crossAxis]] = currentLead + (lineHeight - childHeight) / 2; } else if (alignContentAlignItem == CSSAlign.STRETCH) { child.layout.position[pos[crossAxis]] = currentLead + child.style.margin.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]); // TODO(prenaux): Correctly set the height of items with indefinite // (auto) crossAxis dimension. } } } currentLead += lineHeight; } } // STEP 9: COMPUTING FINAL DIMENSIONS node.layout.measuredDimensions[DIMENSION_WIDTH] = boundAxis(node, CSS_FLEX_DIRECTION_ROW, availableWidth - marginAxisRow); node.layout.measuredDimensions[DIMENSION_HEIGHT] = boundAxis(node, CSS_FLEX_DIRECTION_COLUMN, availableHeight - marginAxisColumn); // If the user didn't specify a width or height for the node, set the // dimensions based on the children. if (measureModeMainDim == CSSMeasureMode.UNDEFINED) { // Clamp the size to the min/max size, if specified, and make sure it // doesn't go below the padding and border amount. node.layout.measuredDimensions[dim[mainAxis]] = boundAxis(node, mainAxis, maxLineMainDim); } else if (measureModeMainDim == CSSMeasureMode.AT_MOST) { node.layout.measuredDimensions[dim[mainAxis]] = Math.max( Math.min(availableInnerMainDim + paddingAndBorderAxisMain, boundAxisWithinMinAndMax(node, mainAxis, maxLineMainDim)), paddingAndBorderAxisMain); } if (measureModeCrossDim == CSSMeasureMode.UNDEFINED) { // Clamp the size to the min/max size, if specified, and make sure it // doesn't go below the padding and border amount. node.layout.measuredDimensions[dim[crossAxis]] = boundAxis(node, crossAxis, totalLineCrossDim + paddingAndBorderAxisCross); } else if (measureModeCrossDim == CSSMeasureMode.AT_MOST) { node.layout.measuredDimensions[dim[crossAxis]] = Math.max( Math.min(availableInnerCrossDim + paddingAndBorderAxisCross, boundAxisWithinMinAndMax(node, crossAxis, totalLineCrossDim + paddingAndBorderAxisCross)), paddingAndBorderAxisCross); } // STEP 10: SIZING AND POSITIONING ABSOLUTE CHILDREN currentAbsoluteChild = firstAbsoluteChild; while (currentAbsoluteChild != null) { // Now that we know the bounds of the container, perform layout again on the // absolutely-positioned children. if (performLayout) { childWidth = CSSConstants.UNDEFINED; childHeight = CSSConstants.UNDEFINED; if ((currentAbsoluteChild.style.dimensions[dim[CSS_FLEX_DIRECTION_ROW]] >= 0.0)) { childWidth = currentAbsoluteChild.style.dimensions[DIMENSION_WIDTH] + (currentAbsoluteChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + currentAbsoluteChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); } else { // If the child doesn't have a specified width, compute the width based on the left/right offsets if they're defined. if (!Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW])) && !Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW]))) { childWidth = node.layout.measuredDimensions[DIMENSION_WIDTH] - (node.style.border.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + node.style.border.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])) - ((Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW])) ? 0 : currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW])) + (Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])) ? 0 : currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW]))); childWidth = boundAxis(currentAbsoluteChild, CSS_FLEX_DIRECTION_ROW, childWidth); } } if ((currentAbsoluteChild.style.dimensions[dim[CSS_FLEX_DIRECTION_COLUMN]] >= 0.0)) { childHeight = currentAbsoluteChild.style.dimensions[DIMENSION_HEIGHT] + (currentAbsoluteChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + currentAbsoluteChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); } else { // If the child doesn't have a specified height, compute the height based on the top/bottom offsets if they're defined. if (!Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN])) && !Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN]))) { childHeight = node.layout.measuredDimensions[DIMENSION_HEIGHT] - (node.style.border.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + node.style.border.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])) - ((Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN])) ? 0 : currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN])) + (Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])) ? 0 : currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN]))); childHeight = boundAxis(currentAbsoluteChild, CSS_FLEX_DIRECTION_COLUMN, childHeight); } } // If we're still missing one or the other dimension, measure the content. if (Float.isNaN(childWidth) || Float.isNaN(childHeight)) { childWidthMeasureMode = Float.isNaN(childWidth) ? CSSMeasureMode.UNDEFINED : CSSMeasureMode.EXACTLY; childHeightMeasureMode = Float.isNaN(childHeight) ? CSSMeasureMode.UNDEFINED : CSSMeasureMode.EXACTLY; // According to the spec, if the main size is not definite and the // child's inline axis is parallel to the main axis (i.e. it's // horizontal), the child should be sized using "UNDEFINED" in // the main size. Otherwise use "AT_MOST" in the cross axis. if (!isMainAxisRow && Float.isNaN(childWidth) && !Float.isNaN(availableInnerWidth)) { childWidth = availableInnerWidth; childWidthMeasureMode = CSSMeasureMode.AT_MOST; } layoutNodeInternal(layoutContext, currentAbsoluteChild, childWidth, childHeight, direction, childWidthMeasureMode, childHeightMeasureMode, false, "abs-measure"); childWidth = currentAbsoluteChild.layout.measuredDimensions[DIMENSION_WIDTH] + (currentAbsoluteChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_ROW], leading[CSS_FLEX_DIRECTION_ROW]) + currentAbsoluteChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_ROW], trailing[CSS_FLEX_DIRECTION_ROW])); childHeight = currentAbsoluteChild.layout.measuredDimensions[DIMENSION_HEIGHT] + (currentAbsoluteChild.style.margin.getWithFallback(leadingSpacing[CSS_FLEX_DIRECTION_COLUMN], leading[CSS_FLEX_DIRECTION_COLUMN]) + currentAbsoluteChild.style.margin.getWithFallback(trailingSpacing[CSS_FLEX_DIRECTION_COLUMN], trailing[CSS_FLEX_DIRECTION_COLUMN])); } layoutNodeInternal(layoutContext, currentAbsoluteChild, childWidth, childHeight, direction, CSSMeasureMode.EXACTLY, CSSMeasureMode.EXACTLY, true, "abs-layout"); if (!Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])) && Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[mainAxis], leading[mainAxis]))) { currentAbsoluteChild.layout.position[leading[mainAxis]] = node.layout.measuredDimensions[dim[mainAxis]] - currentAbsoluteChild.layout.measuredDimensions[dim[mainAxis]] - (Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])) ? 0 : currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[mainAxis], trailing[mainAxis])); } if (!Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis])) && Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(leadingSpacing[crossAxis], leading[crossAxis]))) { currentAbsoluteChild.layout.position[leading[crossAxis]] = node.layout.measuredDimensions[dim[crossAxis]] - currentAbsoluteChild.layout.measuredDimensions[dim[crossAxis]] - (Float.isNaN(currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis])) ? 0 : currentAbsoluteChild.style.position.getWithFallback(trailingSpacing[crossAxis], trailing[crossAxis])); } } currentAbsoluteChild = currentAbsoluteChild.nextChild; } // STEP 11: SETTING TRAILING POSITIONS FOR CHILDREN if (performLayout) { boolean needsMainTrailingPos = false; boolean needsCrossTrailingPos = false; if (mainAxis == CSS_FLEX_DIRECTION_ROW_REVERSE || mainAxis == CSS_FLEX_DIRECTION_COLUMN_REVERSE) { needsMainTrailingPos = true; } if (crossAxis == CSS_FLEX_DIRECTION_ROW_REVERSE || crossAxis == CSS_FLEX_DIRECTION_COLUMN_REVERSE) { needsCrossTrailingPos = true; } // Set trailing position if necessary. if (needsMainTrailingPos || needsCrossTrailingPos) { for (i = 0; i < childCount; ++i) { child = node.getChildAt(i); if (needsMainTrailingPos) { child.layout.position[trailing[mainAxis]] = node.layout.measuredDimensions[dim[mainAxis]] - child.layout.measuredDimensions[dim[mainAxis]] - child.layout.position[pos[mainAxis]]; } if (needsCrossTrailingPos) { child.layout.position[trailing[crossAxis]] = node.layout.measuredDimensions[dim[crossAxis]] - child.layout.measuredDimensions[dim[crossAxis]] - child.layout.position[pos[crossAxis]]; } } } } } }