| /* |
| * Copyright (C) 2018 Apple Inc. All Rights Reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY |
| * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR |
| * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY |
| * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| /* |
| class BlockMarginCollapse { |
| public: |
| LayoutUnit marginTop(const Layout::Box&); |
| LayoutUnit marginBottom(const Layout::Box&); |
| |
| private: |
| bool isMarginTopCollapsedWithSibling(const Layout::Box&); |
| bool isMarginBottomCollapsedWithSibling(const Layout::Box&); |
| bool isMarginTopCollapsedWithParent(const Layout::Box&); |
| bool isMarginBottomCollapsedWithParent(const Layout::Box&); |
| |
| LayoutUnit nonCollapsedMarginTop(const Layout::Box&); |
| LayoutUnit nonCollapsedMarginBottom(const Layout::Box&); |
| LayoutUnit collapsedMarginTopFromFirstChild(const Layout::Box&); |
| LayoutUnit collapsedMarginBottomFromLastChild(const Layout::Box&); |
| LayoutUnit marginValue(currentMarginValue, candidateMarginValue); |
| |
| bool hasAdjoiningMarginTopAndBottom(const Layout::Box&); |
| }; |
| */ |
| class BlockMarginCollapse { |
| |
| static marginTop(layoutBox) { |
| if (layoutBox.isAnonymous()) |
| return 0; |
| // TODO: take _hasAdjoiningMarginTopAndBottom() into account. |
| if (this._isMarginTopCollapsedWithParent(layoutBox)) |
| return 0; |
| // Floats and out of flow positioned boxes do not collapse their margins. |
| if (!this._isMarginTopCollapsedWithSibling(layoutBox)) |
| return this._nonCollapsedMarginTop(layoutBox); |
| // The bottom margin of an in-flow block-level element always collapses with the top margin of its next in-flow block-level sibling, |
| // unless that sibling has clearance. |
| let previousInFlowSibling = layoutBox.previousInFlowSibling(); |
| if (previousInFlowSibling) { |
| let previousSiblingMarginBottom = this._nonCollapsedMarginBottom(previousInFlowSibling); |
| let marginTop = this._nonCollapsedMarginTop(layoutBox); |
| return this._marginValue(marginTop, previousSiblingMarginBottom); |
| } |
| return this._nonCollapsedMarginTop(layoutBox); |
| } |
| |
| static marginBottom(layoutBox) { |
| if (layoutBox.isAnonymous()) |
| return 0; |
| // TODO: take _hasAdjoiningMarginTopAndBottom() into account. |
| if (this._isMarginBottomCollapsedWithParent(layoutBox)) |
| return 0; |
| // Floats and out of flow positioned boxes do not collapse their margins. |
| if (!this._isMarginBottomCollapsedWithSibling(layoutBox)) |
| return this._nonCollapsedMarginBottom(layoutBox); |
| // The bottom margin of an in-flow block-level element always collapses with the top margin of its next in-flow block-level sibling, |
| // unless that sibling has clearance. |
| if (layoutBox.nextInFlowSibling()) |
| return 0; |
| return this._nonCollapsedMarginBottom(layoutBox); |
| } |
| |
| static _isMarginTopCollapsedWithSibling(layoutBox) { |
| if (layoutBox.isFloatingPositioned()) |
| return false; |
| if (!layoutBox.isPositioned() || layoutBox.isInFlowPositioned()) |
| return true; |
| // Out of flow positioned. |
| ASSERT(layoutBox.isOutOfFlowPositioned()); |
| return Utils.isTopAuto(layoutBox); |
| } |
| |
| static _isMarginBottomCollapsedWithSibling(layoutBox) { |
| if (layoutBox.isFloatingPositioned()) |
| return false; |
| if (!layoutBox.isPositioned() || layoutBox.isInFlowPositioned()) |
| return true; |
| // Out of flow positioned. |
| ASSERT(layoutBox.isOutOfFlowPositioned()); |
| return Utils.isBottomAuto(layoutBox); |
| } |
| |
| static _isMarginTopCollapsedWithParent(layoutBox) { |
| // The first inflow child could propagate its top margin to parent. |
| // https://www.w3.org/TR/CSS21/box.html#collapsing-margins |
| if (layoutBox.isAnonymous()) |
| return false; |
| if (layoutBox.isFloatingOrOutOfFlowPositioned()) |
| return false; |
| let parent = layoutBox.parent(); |
| // Is this box the first inlflow child? |
| if (parent.firstInFlowChild() != layoutBox) |
| return false; |
| if (parent.establishesBlockFormattingContext()) |
| return false; |
| // Margins of the root element's box do not collapse. |
| if (parent.isRootBox()) |
| return false; |
| if (Utils.hasBorderTop(parent)) |
| return false; |
| if (Utils.hasPaddingTop(parent)) |
| return false; |
| return true; |
| } |
| |
| static _isMarginBottomCollapsedWithParent(layoutBox) { |
| // last inflow box to parent. |
| // https://www.w3.org/TR/CSS21/box.html#collapsing-margins |
| if (layoutBox.isAnonymous()) |
| return false; |
| if (layoutBox.isFloatingOrOutOfFlowPositioned()) |
| return false; |
| let parent = layoutBox.parent(); |
| // Is this the last inlflow child? |
| if (parent.lastInFlowChild() != layoutBox) |
| return false; |
| if (parent.establishesBlockFormattingContext()) |
| return false; |
| // Margins of the root element's box do not collapse. |
| if (parent.isRootBox()) |
| return false; |
| if (Utils.hasBorderTop(parent)) |
| return false; |
| if (Utils.hasPaddingTop(parent)) |
| return false; |
| if (!Utils.isHeightAuto(parent)) |
| return false; |
| return true; |
| } |
| |
| static _nonCollapsedMarginTop(layoutBox) { |
| // Non collapsed margin top includes collapsed margin from inflow first child. |
| return this._marginValue(Utils.computedMarginTop(layoutBox.node()), this._collapsedMarginTopFromFirstChild(layoutBox)); |
| } |
| |
| static _nonCollapsedMarginBottom(layoutBox) { |
| // Non collapsed margin bottom includes collapsed margin from inflow last child. |
| return this._marginValue(Utils.computedMarginBottom(layoutBox.node()), this._collapsedMarginBottomFromLastChild(layoutBox)); |
| } |
| |
| static _collapsedMarginTopFromFirstChild(layoutBox) { |
| // Check if the first child collapses its margin top. |
| if (!layoutBox.isContainer() || !layoutBox.firstInFlowChild()) |
| return 0; |
| let firstInFlowChild = layoutBox.firstInFlowChild(); |
| if (!this._isMarginTopCollapsedWithParent(firstInFlowChild)) |
| return 0; |
| // Collect collapsed margin top recursively. |
| return this._marginValue(Utils.computedMarginTop(firstInFlowChild.node()), this._collapsedMarginTopFromFirstChild(firstInFlowChild)); |
| } |
| |
| static _collapsedMarginBottomFromLastChild(layoutBox) { |
| // Check if the last child propagates its margin bottom. |
| if (!layoutBox.isContainer() || !layoutBox.lastInFlowChild()) |
| return 0; |
| let lastInFlowChild = layoutBox.lastInFlowChild(); |
| if (!this._isMarginBottomCollapsedWithParent(lastInFlowChild)) |
| return 0; |
| // Collect collapsed margin bottom recursively. |
| return this._marginValue(Utils.computedMarginBottom(lastInFlowChild.node()), this._collapsedMarginBottomFromLastChild(lastInFlowChild)); |
| } |
| |
| static _marginValue(currentMarginValue, candidateMarginValue) { |
| if (!candidateMarginValue) |
| return currentMarginValue; |
| if (!currentMarginValue) |
| return candidateMarginValue; |
| // Both margins are positive. |
| if (candidateMarginValue > 0 && currentMarginValue > 0) |
| return Math.max(candidateMarginValue, currentMarginValue) |
| // Both margins are negative. |
| if (candidateMarginValue < 0 && currentMarginValue < 0) |
| return 0 - Math.max(Math.abs(candidateMarginValue), Math.abs(currentMarginValue)) |
| // One of the margins is negative. |
| return currentMarginValue + candidateMarginValue; |
| } |
| |
| static _hasAdjoiningMarginTopAndBottom(layoutBox) { |
| // Two margins are adjoining if and only if: |
| // 1. both belong to in-flow block-level boxes that participate in the same block formatting context |
| // 2. no line boxes, no clearance, no padding and no border separate them (Note that certain zero-height line boxes (see 9.4.2) are ignored for this purpose.) |
| // 3. both belong to vertically-adjacent box edges, i.e. form one of the following pairs: |
| // top margin of a box and top margin of its first in-flow child |
| // bottom margin of box and top margin of its next in-flow following sibling |
| // bottom margin of a last in-flow child and bottom margin of its parent if the parent has 'auto' computed height |
| // top and bottom margins of a box that does not establish a new block formatting context and that has zero computed 'min-height', |
| // zero or 'auto' computed 'height', and no in-flow children |
| // A collapsed margin is considered adjoining to another margin if any of its component margins is adjoining to that margin. |
| return false; |
| } |
| } |
