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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
// Description: Provides paragraph level margin collapsing support.
//
using System;
namespace MS.Internal.PtsHost
{
// ----------------------------------------------------------------------
// MarginCollapsingState class provides paragraph level margin collapsing
// support.
//
// Adjoining vertical margins of two paragraphs collapse. The resulting
// margin width is the maximum of the adjoining margin widths. In the case
// of negative margins, the absolute maximum of the negative adjoining
// margins is deducted from the maximum of the positive adjoining margins.
// If there are no positive margins, the absolute maximum of the negative
// adjoining margins is deducted from zero.
// ----------------------------------------------------------------------
internal sealed class MarginCollapsingState : UnmanagedHandle
{
// ------------------------------------------------------------------
// Create new margin collapsing state and collapse margins if necessary.
// If no collapsing happens, retrieve margin from old collapsing state.
// This margin value should be used to advance pen.
// ------------------------------------------------------------------
internal static void CollapseTopMargin(
PtsContext ptsContext, // Current PTS Context.
MbpInfo mbp, // MBP information for element entering the scope
MarginCollapsingState mcsCurrent, // current margin collapsing state (adjacent to the new one).
out MarginCollapsingState mcsNew, // margin collapsing state for element entering the scope
out int margin) // collapsed margin value
{
margin = 0;
mcsNew = null;
// Create new margin collapsing info
mcsNew = new MarginCollapsingState(ptsContext, mbp.MarginTop);
// collapse margins, if current margin collapsing exists
if (mcsCurrent != null)
{
mcsNew.Collapse(mcsCurrent);
}
// If border or paddind is specified:
// (1) get collapsed margin value
// (2) set new mcs to null, because we don't have one anymore
if (mbp.BPTop != 0)
{
margin = mcsNew.Margin;
mcsNew.Dispose();
mcsNew = null;
}
else if (mcsCurrent == null && DoubleUtil.IsZero(mbp.Margin.Top))
{
// No need to create new margin collapsing info
mcsNew.Dispose();
mcsNew = null;
}
}
// ------------------------------------------------------------------
// Update current margin collapsing state and collapse margins if
// necessary. If no collapsing happens, retrieve margin from previous
// collapsing state. This margin value should be used to advance pen.
// ------------------------------------------------------------------
internal static void CollapseBottomMargin(
PtsContext ptsContext, // Current PTS Context.
MbpInfo mbp, // MBP information for element leaving the scope
MarginCollapsingState mcsCurrent, // current margin collapsing state (adjacent to the new one).
out MarginCollapsingState mcsNew, // margin collapsing state for element leaving the scope
out int margin) // collapsed margin value
{
margin = 0;
mcsNew = null;
// Create new margin collapsing state, if necessary
if (!DoubleUtil.IsZero(mbp.Margin.Bottom))
{
mcsNew = new MarginCollapsingState(ptsContext, mbp.MarginBottom);
}
// If the current margin collapsing state does not exist, we are done.
// Otherwise, get current border and padding and decide if to collapse margin.
if (mcsCurrent != null)
{
if (mbp.BPBottom != 0)
{
// No collapsing happens, get margin value
margin = mcsCurrent.Margin;
}
else
{
// Collapse margins
if (mcsNew == null)
{
mcsNew = new MarginCollapsingState(ptsContext, 0);
}
mcsNew.Collapse(mcsCurrent);
}
}
}
// ------------------------------------------------------------------
// Constructor.
//
// ptsContext - Current PTS context.
// margin - margin value
// ------------------------------------------------------------------
internal MarginCollapsingState(PtsContext ptsContext, int margin) : base(ptsContext)
{
_maxPositive = (margin >= 0) ? margin : 0;
_minNegative = (margin < 0) ? margin : 0;
}
// ------------------------------------------------------------------
// Constructor. Make identical copy of the margin collapsing state.
//
// mcs - margin collapsing state to copy
// ------------------------------------------------------------------
private MarginCollapsingState(MarginCollapsingState mcs) : base(mcs.PtsContext)
{
_maxPositive = mcs._maxPositive;
_minNegative = mcs._minNegative;
}
// ------------------------------------------------------------------
// Make identical copy of the margin collapsing state.
//
// Returns: identical copy of margin collapsing state.
// ------------------------------------------------------------------
internal MarginCollapsingState Clone()
{
return new MarginCollapsingState(this);
}
// ------------------------------------------------------------------
// Compare margin collapsing state with another one.
//
// mcs - another margin collapsing state
//
// Returns: 'true' if both are the same.
// ------------------------------------------------------------------
internal bool IsEqual(MarginCollapsingState mcs)
{
return (_maxPositive == mcs._maxPositive && _minNegative == mcs._minNegative);
}
// ------------------------------------------------------------------
// The resulting margin width is the maximum of the adjoining margin
// widths. In the case of negative margins, the absolute maximum of
// the negative adjoining margins is deducted from the maximum of
// the positive adjoining margins. If there are no positive margins,
// the absolute maximum of the negative adjoining margins is deducted
// from zero.
//
// mcs - margin collapsing state to collapse with
// ------------------------------------------------------------------
internal void Collapse(MarginCollapsingState mcs)
{
_maxPositive = Math.Max(_maxPositive, mcs._maxPositive);
_minNegative = Math.Min(_minNegative, mcs._minNegative);
}
// ------------------------------------------------------------------
// The resulting margin width is the maximum of the adjoining margin
// widths. In the case of negative margins, the absolute maximum of
// the negative adjoining margins is deducted from the maximum of
// the positive adjoining margins. If there are no positive margins,
// the absolute maximum of the negative adjoining margins is deducted
// from zero.
//
// margin - margin value to collapse with
// ------------------------------------------------------------------
//internal void Collapse(int margin)
//{
// _maxPositive = Math.Max(_maxPositive, margin);
// _minNegative = Math.Min(_minNegative, margin);
//}
// ------------------------------------------------------------------
// Actual margin value.
// ------------------------------------------------------------------
internal int Margin { get { return _maxPositive + _minNegative; } }
// ------------------------------------------------------------------
// Maximum positive and minimum negative value for margin.
// ------------------------------------------------------------------
private int _maxPositive;
private int _minNegative;
}
}
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