| /* |
| * Copyright (C) 2012 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 COMPUTER, 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. |
| */ |
| |
| #ifndef LayoutMultiColumnFlowThread_h |
| #define LayoutMultiColumnFlowThread_h |
| |
| #include "core/CoreExport.h" |
| #include "core/layout/FragmentationContext.h" |
| #include "core/layout/LayoutFlowThread.h" |
| |
| namespace blink { |
| |
| class LayoutMultiColumnSet; |
| class LayoutMultiColumnSpannerPlaceholder; |
| |
| // What to translate *to* when translating from a flow thread coordinate space. |
| enum class CoordinateSpaceConversion { |
| // Just translate to the nearest containing coordinate space (i.e. where our |
| // multicol container lives) of this flow thread, i.e. don't walk ancestral |
| // flow threads, if any. |
| Containing, |
| |
| // Translate to visual coordinates, by walking all ancestral flow threads. |
| Visual |
| }; |
| |
| // Flow thread implementation for CSS multicol. This will be inserted as an |
| // anonymous child block of the actual multicol container (i.e. the |
| // LayoutBlockFlow whose style computes to non-auto column-count and/or |
| // column-width). LayoutMultiColumnFlowThread is the heart of the multicol |
| // implementation, and there is only one instance per multicol container. Child |
| // content of the multicol container is parented into the flow thread at the |
| // time of layoutObject insertion. |
| // |
| // Apart from this flow thread child, the multicol container will also have |
| // LayoutMultiColumnSet children, which are used to position the columns |
| // visually. The flow thread is in charge of layout, and, after having |
| // calculated the column width, it lays out content as if everything were in one |
| // tall single column, except that there will typically be some amount of blank |
| // space (also known as pagination struts) at the offsets where the actual |
| // column boundaries are. This way, content that needs to be preceded by a break |
| // will appear at the top of the next column. Content needs to be preceded by a |
| // break when there's a forced break or when the content is unbreakable and |
| // cannot fully fit in the same column as the preceding piece of content. |
| // Although a LayoutMultiColumnFlowThread is laid out, it does not take up any |
| // space in its container. It's the LayoutMultiColumnSet objects that take up |
| // the necessary amount of space, and make sure that the columns are painted and |
| // hit-tested correctly. |
| // |
| // If there is any column content inside the multicol container, we create a |
| // LayoutMultiColumnSet. We only need to create multiple sets if there are |
| // spanners (column-span:all) in the multicol container. When a spanner is |
| // inserted, content preceding it gets its own set, and content succeeding it |
| // will get another set. The spanner itself will also get its own placeholder |
| // between the sets (LayoutMultiColumnSpannerPlaceholder), so that it gets |
| // positioned and sized correctly. The column-span:all element is inside the |
| // flow thread, but its containing block is the multicol container. |
| // |
| // Some invariants for the layout tree structure for multicol: |
| // - A multicol container is always a LayoutBlockFlow |
| // - Every multicol container has one and only one LayoutMultiColumnFlowThread |
| // - All multicol DOM children and pseudo-elements associated with the multicol |
| // container are reparented into the flow thread. |
| // - The LayoutMultiColumnFlowThread is the first child of the multicol |
| // container. |
| // - A multicol container may only have LayoutMultiColumnFlowThread, |
| // LayoutMultiColumnSet and LayoutMultiColumnSpannerPlaceholder children. |
| // - A LayoutMultiColumnSet may not be adjacent to another LayoutMultiColumnSet; |
| // there are no use-cases for it, and there are also implementation |
| // limitations behind this requirement. |
| // - The flow thread is not in the containing block chain for children that are |
| // not to be laid out in columns. This means column spanners and absolutely |
| // positioned children whose containing block is outside column content |
| // - Each spanner (column-span:all) establishes a |
| // LayoutMultiColumnSpannerPlaceholder |
| // |
| // The width of the flow thread is the same as the column width. The width of a |
| // column set is the same as the content box width of the multicol container; in |
| // other words exactly enough to hold the number of columns to be used, stacked |
| // horizontally, plus column gaps between them. |
| // |
| // Since it's the first child of the multicol container, the flow thread is laid |
| // out first, albeit in a slightly special way, since it's not to take up any |
| // space in its ancestors. Afterwards, the column sets are laid out. Column sets |
| // get their height from the columns that they hold. In single column-row |
| // constrained height non-balancing cases without spanners this will simply be |
| // the same as the content height of the multicol container itself. In most |
| // other cases we'll have to calculate optimal column heights ourselves, though. |
| // This process is referred to as column balancing, and then we infer the column |
| // set height from the height of the flow thread portion occupied by each set. |
| // |
| // More on column balancing: the columns' height is unknown in the first layout |
| // pass when balancing. This means that we cannot insert any implicit (soft / |
| // unforced) breaks (and pagination struts) when laying out the contents of the |
| // flow thread. We'll just lay out everything in tall single strip. After the |
| // initial flow thread layout pass we can determine a tentative / minimal / |
| // initial column height. This is calculated by simply dividing the flow |
| // thread's height by the number of specified columns. In the layout pass that |
| // follows, we can insert breaks (and pagination struts) at column boundaries, |
| // since we now have a column height. |
| // It may very easily turn out that the calculated height wasn't enough, though. |
| // We'll notice this at end of layout. If we end up with too many columns (i.e. |
| // columns overflowing the multicol container), it wasn't enough. In this case |
| // we need to increase the column heights. We'll increase them by the lowest |
| // amount of space that could possibly affect where the breaks occur. We'll |
| // relayout (to find new break points and the new lowest amount of space |
| // increase that could affect where they occur, in case we need another round) |
| // until we've reached an acceptable height (where everything fits perfectly in |
| // the number of columns that we have specified). The rule of thumb is that we |
| // shouldn't have to perform more of such iterations than the number of columns |
| // that we have. |
| // |
| // For each layout iteration done for column balancing, the flow thread will |
| // need a deep layout if column heights changed in the previous pass, since |
| // column height changes may affect break points and pagination struts anywhere |
| // in the tree, and currently no way exists to do this in a more optimized |
| // manner. |
| // |
| // There's also some documentation online: |
| // https://www.chromium.org/developers/design-documents/multi-column-layout |
| class CORE_EXPORT LayoutMultiColumnFlowThread : public LayoutFlowThread, |
| public FragmentationContext { |
| public: |
| ~LayoutMultiColumnFlowThread() override; |
| |
| static LayoutMultiColumnFlowThread* createAnonymous( |
| Document&, |
| const ComputedStyle& parentStyle); |
| |
| bool isLayoutMultiColumnFlowThread() const final { return true; } |
| |
| LayoutBlockFlow* multiColumnBlockFlow() const { |
| return toLayoutBlockFlow(parent()); |
| } |
| |
| LayoutMultiColumnSet* firstMultiColumnSet() const; |
| LayoutMultiColumnSet* lastMultiColumnSet() const; |
| |
| // Return the first column set or spanner placeholder. |
| LayoutBox* firstMultiColumnBox() const { return nextSiblingBox(); } |
| // Return the last column set or spanner placeholder. |
| LayoutBox* lastMultiColumnBox() const { |
| LayoutBox* lastSiblingBox = multiColumnBlockFlow()->lastChildBox(); |
| // The flow thread is the first child of the multicol container. If the flow |
| // thread is also the last child, it means that there are no siblings; i.e. |
| // we have no column boxes. |
| return lastSiblingBox != this ? lastSiblingBox : 0; |
| } |
| |
| // Find the first set inside which the specified layoutObject (which is a |
| // flowthread descendant) would be rendered. |
| LayoutMultiColumnSet* mapDescendantToColumnSet(LayoutObject*) const; |
| |
| // Return the spanner placeholder that belongs to the spanner in the |
| // containing block chain, if any. This includes the layoutObject for the |
| // element that actually establishes the spanner too. |
| LayoutMultiColumnSpannerPlaceholder* containingColumnSpannerPlaceholder( |
| const LayoutObject* descendant) const; |
| |
| // Populate the flow thread with what's currently its siblings. Called when a |
| // regular block becomes a multicol container. |
| void populate(); |
| |
| // Empty the flow thread by moving everything to the parent. Remove all |
| // multicol specific layoutObjects. Then destroy the flow thread. Called when |
| // a multicol container becomes a regular block. |
| void evacuateAndDestroy(); |
| |
| unsigned columnCount() const { return m_columnCount; } |
| |
| // Total height available to columns and spanners. This is the multicol |
| // container's content box logical height, or 0 if auto. |
| LayoutUnit columnHeightAvailable() const { return m_columnHeightAvailable; } |
| void setColumnHeightAvailable(LayoutUnit available) { |
| m_columnHeightAvailable = available; |
| } |
| |
| // Maximum content box logical height for the multicol container. This takes |
| // CSS logical 'height' and 'max-height' into account. LayoutUnit::max() is |
| // returned if nothing constrains the height of the multicol container. This |
| // method only deals with used values of CSS properties, and it does not |
| // consider enclosing fragmentation contexts -- that's something that needs to |
| // be calculated per fragmentainer group. |
| LayoutUnit maxColumnLogicalHeight() const; |
| |
| bool progressionIsInline() const { return m_progressionIsInline; } |
| |
| LayoutUnit tallestUnbreakableLogicalHeight( |
| LayoutUnit offsetInFlowThread) const; |
| |
| LayoutSize columnOffset(const LayoutPoint&) const final; |
| |
| // Do we need to set a new width and lay out? |
| virtual bool needsNewWidth() const; |
| |
| bool isPageLogicalHeightKnown() const final; |
| bool mayHaveNonUniformPageLogicalHeight() const final; |
| |
| LayoutSize flowThreadTranslationAtOffset(LayoutUnit, |
| PageBoundaryRule, |
| CoordinateSpaceConversion) const; |
| LayoutSize flowThreadTranslationAtPoint(const LayoutPoint& flowThreadPoint, |
| CoordinateSpaceConversion) const; |
| |
| LayoutPoint flowThreadPointToVisualPoint( |
| const LayoutPoint& flowThreadPoint) const override; |
| LayoutPoint visualPointToFlowThreadPoint( |
| const LayoutPoint& visualPoint) const override; |
| |
| int inlineBlockBaseline(LineDirectionMode) const override; |
| |
| LayoutMultiColumnSet* columnSetAtBlockOffset(LayoutUnit, |
| PageBoundaryRule) const final; |
| |
| void layoutColumns(SubtreeLayoutScope&); |
| |
| // Skip past a column spanner during flow thread layout. Spanners are not laid |
| // out inside the flow thread, since the flow thread is not in a spanner's |
| // containing block chain (since the containing block is the multicol |
| // container). |
| void skipColumnSpanner(LayoutBox*, LayoutUnit logicalTopInFlowThread); |
| |
| // Returns true if at least one column got a new height after flow thread |
| // layout (during column set layout), in which case we need another layout |
| // pass. Column heights may change after flow thread layout because of |
| // balancing. We may have to do multiple layout passes, depending on how the |
| // contents is fitted to the changed column heights. In most cases, laying out |
| // again twice or even just once will suffice. Sometimes we need more passes |
| // than that, though, but the number of retries should not exceed the number |
| // of columns, unless we have a bug. |
| bool columnHeightsChanged() const { return m_columnHeightsChanged; } |
| void setColumnHeightsChanged() { m_columnHeightsChanged = true; } |
| |
| void columnRuleStyleDidChange(); |
| |
| // Remove the spanner placeholder and return true if the specified object is |
| // no longer a valid spanner. |
| bool removeSpannerPlaceholderIfNoLongerValid( |
| LayoutBox* spannerObjectInFlowThread); |
| |
| LayoutMultiColumnFlowThread* enclosingFlowThread() const; |
| FragmentationContext* enclosingFragmentationContext() const; |
| LayoutUnit blockOffsetInEnclosingFragmentationContext() const { |
| ASSERT(enclosingFragmentationContext()); |
| return m_blockOffsetInEnclosingFragmentationContext; |
| } |
| |
| // If we've run out of columns in the last fragmentainer group (column row), |
| // we have to insert another fragmentainer group in order to hold more |
| // columns. This means that we're moving to the next outer column (in the |
| // enclosing fragmentation context). |
| void appendNewFragmentainerGroupIfNeeded(LayoutUnit offsetInFlowThread, |
| PageBoundaryRule); |
| |
| // Implementing FragmentationContext: |
| bool isFragmentainerLogicalHeightKnown() final; |
| LayoutUnit fragmentainerLogicalHeightAt(LayoutUnit blockOffset) final; |
| LayoutUnit remainingLogicalHeightAt(LayoutUnit blockOffset) final; |
| LayoutMultiColumnFlowThread* associatedFlowThread() final { return this; } |
| |
| const char* name() const override { return "LayoutMultiColumnFlowThread"; } |
| |
| protected: |
| LayoutMultiColumnFlowThread(); |
| void setProgressionIsInline(bool isInline) { |
| m_progressionIsInline = isInline; |
| } |
| |
| void layout() override; |
| |
| private: |
| void calculateColumnHeightAvailable(); |
| void calculateColumnCountAndWidth(LayoutUnit& width, unsigned& count) const; |
| void createAndInsertMultiColumnSet(LayoutBox* insertBefore = nullptr); |
| void createAndInsertSpannerPlaceholder( |
| LayoutBox* spannerObjectInFlowThread, |
| LayoutObject* insertedBeforeInFlowThread); |
| void destroySpannerPlaceholder(LayoutMultiColumnSpannerPlaceholder*); |
| virtual bool descendantIsValidColumnSpanner(LayoutObject* descendant) const; |
| |
| void addColumnSetToThread(LayoutMultiColumnSet*) override; |
| void willBeRemovedFromTree() override; |
| void flowThreadDescendantWasInserted(LayoutObject*) final; |
| void flowThreadDescendantWillBeRemoved(LayoutObject*) final; |
| void flowThreadDescendantStyleWillChange( |
| LayoutBox*, |
| StyleDifference, |
| const ComputedStyle& newStyle) override; |
| void flowThreadDescendantStyleDidChange( |
| LayoutBox*, |
| StyleDifference, |
| const ComputedStyle& oldStyle) override; |
| void toggleSpannersInSubtree(LayoutBox*); |
| void computePreferredLogicalWidths() override; |
| void computeLogicalHeight(LayoutUnit logicalHeight, |
| LayoutUnit logicalTop, |
| LogicalExtentComputedValues&) const override; |
| void updateLogicalWidth() override; |
| void contentWasLaidOut( |
| LayoutUnit logicalBottomInFlowThreadAfterPagination) override; |
| bool canSkipLayout(const LayoutBox&) const override; |
| MultiColumnLayoutState multiColumnLayoutState() const override; |
| void restoreMultiColumnLayoutState(const MultiColumnLayoutState&) override; |
| |
| // The last set we worked on. It's not to be used as the "current set". The |
| // concept of a "current set" is difficult, since layout may jump back and |
| // forth in the tree, due to wrong top location estimates (due to e.g. margin |
| // collapsing), and possibly for other reasons. |
| LayoutMultiColumnSet* m_lastSetWorkedOn; |
| |
| #if DCHECK_IS_ON() |
| // Used to check consistency between calls to |
| // flowThreadDescendantStyleWillChange() and |
| // flowThreadDescendantStyleDidChange(). |
| static const LayoutBox* s_styleChangedBox; |
| #endif |
| |
| // The used value of column-count |
| unsigned m_columnCount; |
| // Total height available to columns, or 0 if auto. |
| LayoutUnit m_columnHeightAvailable; |
| |
| // Cached block offset from this flow thread to the enclosing fragmentation |
| // context, if any. In |
| // the coordinate space of the enclosing fragmentation context. |
| LayoutUnit m_blockOffsetInEnclosingFragmentationContext; |
| |
| // Set when column heights are out of sync with actual layout. |
| bool m_columnHeightsChanged; |
| |
| // Always true for regular multicol. False for paged-y overflow. |
| bool m_progressionIsInline; |
| |
| bool m_isBeingEvacuated; |
| |
| // Specifies whether the the descendant whose style is about to change could |
| // contain spanners or not. The flag is set in |
| // flowThreadDescendantStyleWillChange(), and then checked in |
| // flowThreadDescendantStyleDidChange(). |
| static bool s_couldContainSpanners; |
| |
| static bool s_toggleSpannersIfNeeded; |
| }; |
| |
| // Cannot use DEFINE_LAYOUT_OBJECT_TYPE_CASTS here, because |
| // isMultiColumnFlowThread() is defined in LayoutFlowThread, not in |
| // LayoutObject. |
| DEFINE_TYPE_CASTS(LayoutMultiColumnFlowThread, |
| LayoutFlowThread, |
| object, |
| object->isLayoutMultiColumnFlowThread(), |
| object.isLayoutMultiColumnFlowThread()); |
| |
| } // namespace blink |
| |
| #endif // LayoutMultiColumnFlowThread_h |