| /* |
| * 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 RenderMultiColumnFlowThread_h |
| #define RenderMultiColumnFlowThread_h |
| |
| #include "core/rendering/RenderFlowThread.h" |
| #include "wtf/HashMap.h" |
| |
| namespace blink { |
| |
| class RenderMultiColumnSet; |
| class RenderMultiColumnSpannerSet; |
| |
| // Flow thread implementation for CSS multicol. This will be inserted as an anonymous child block of |
| // the actual multicol container (i.e. the RenderBlockFlow whose style computes to non-auto |
| // column-count and/or column-width). RenderMultiColumnFlowThread 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 renderer insertion. |
| // |
| // Apart from this flow thread child, the multicol container will also have RenderMultiColumnSet |
| // "region" 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 RenderMultiColumnFlowThread is laid out, it does not take up any space in its |
| // container. It's the RenderMultiColumnSet 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 |
| // RenderMultiColumnSet. 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 set (RenderMultiColumnSpannerSet). |
| // |
| // 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 (see |
| // RenderMultiColumnSet::recordSpaceShortage()). 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. |
| class RenderMultiColumnFlowThread : public RenderFlowThread { |
| public: |
| virtual ~RenderMultiColumnFlowThread(); |
| |
| static RenderMultiColumnFlowThread* createAnonymous(Document&, RenderStyle* parentStyle); |
| |
| virtual bool isRenderMultiColumnFlowThread() const override final { return true; } |
| |
| RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); } |
| |
| RenderMultiColumnSet* firstMultiColumnSet() const; |
| RenderMultiColumnSet* lastMultiColumnSet() const; |
| |
| // Return the spanner set (if any) that contains the specified renderer. This includes the |
| // renderer for the element that actually establishes the spanner too. |
| RenderMultiColumnSpannerSet* containingColumnSpannerSet(const RenderObject* 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 |
| // renderers. Then destroy the flow thread. Called when a multicol container becomes a regular |
| // block. |
| void evacuateAndDestroy(); |
| |
| unsigned columnCount() const { return m_columnCount; } |
| LayoutUnit columnHeightAvailable() const { return m_columnHeightAvailable; } |
| void setColumnHeightAvailable(LayoutUnit available) { m_columnHeightAvailable = available; } |
| virtual bool heightIsAuto() const { return !columnHeightAvailable() || multiColumnBlockFlow()->style()->columnFill() == ColumnFillBalance; } |
| bool progressionIsInline() const { return m_progressionIsInline; } |
| |
| virtual LayoutSize columnOffset(const LayoutPoint&) const override final; |
| |
| // Do we need to set a new width and lay out? |
| virtual bool needsNewWidth() const; |
| |
| void layoutColumns(bool relayoutChildren, SubtreeLayoutScope&); |
| |
| bool recalculateColumnHeights(); |
| |
| protected: |
| RenderMultiColumnFlowThread(); |
| void setProgressionIsInline(bool isInline) { m_progressionIsInline = isInline; } |
| |
| virtual void layout() override; |
| |
| private: |
| void calculateColumnCountAndWidth(LayoutUnit& width, unsigned& count) const; |
| void createAndInsertMultiColumnSet(); |
| void createAndInsertSpannerSet(RenderBox* spanner); |
| virtual bool descendantIsValidColumnSpanner(RenderObject* descendant) const; |
| |
| virtual const char* renderName() const override; |
| virtual void addRegionToThread(RenderMultiColumnSet*) override; |
| virtual void willBeRemovedFromTree() override; |
| virtual void flowThreadDescendantWasInserted(RenderObject*) override; |
| virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const override; |
| virtual void updateLogicalWidth() override; |
| virtual void setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage) override; |
| virtual void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight) override; |
| virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const override; |
| virtual bool addForcedRegionBreak(LayoutUnit, RenderObject* breakChild, bool isBefore, LayoutUnit* offsetBreakAdjustment = 0) override; |
| virtual bool isPageLogicalHeightKnown() const override; |
| |
| typedef HashMap<const RenderObject*, RenderMultiColumnSpannerSet*> SpannerMap; |
| SpannerMap m_spannerMap; |
| |
| unsigned m_columnCount; // The used value of column-count |
| LayoutUnit m_columnHeightAvailable; // Total height available to columns, or 0 if auto. |
| bool m_inBalancingPass; // Set when relayouting for column balancing. |
| bool m_needsColumnHeightsRecalculation; // Set when we need to recalculate the column set heights after layout. |
| bool m_progressionIsInline; // Always true for regular multicol. False for paged-y overflow. |
| }; |
| |
| } // namespace blink |
| |
| #endif // RenderMultiColumnFlowThread_h |
| |