/// <summary>
/// Builds a highlight geometry object for a given character range.
/// </summary>
/// <param name="origin">The origin of the highlight region.</param>
/// <param name="startIndex">The start index of initial character the bounds should be obtained for.</param>
/// <param name="count">The number of characters the bounds should be obtained for.</param>
/// <returns>Geometry that surrounds the specified character range.</returns>
public Geometry BuildHighlightGeometry(Point origin, int startIndex, int count)
{
ValidateRange(startIndex, count);
PathGeometry accumulatedBounds = null;
using (LineEnumerator enumerator = GetEnumerator())
{
Point lineOrigin = origin;
while (enumerator.MoveNext())
{
using (TextLine currentLine = enumerator.Current)
{
int x0 = Math.Max(enumerator.Position, startIndex);
int x1 = Math.Min(enumerator.Position + enumerator.Length, startIndex + count);
// check if this line is intersects with the specified character range
if (x0 < x1)
{
IList<TextBounds> highlightBounds = currentLine.GetTextBounds(
x0,
x1 - x0
);
if (highlightBounds != null)
{
foreach (TextBounds bound in highlightBounds)
{
Rect rect = bound.Rectangle;
if (FlowDirection == FlowDirection.RightToLeft)
{
// Convert logical units (which extend leftward from the right edge
// of the paragraph) to physical units.
//
// Note that since rect is in logical units, rect.Right corresponds to
// the visual *left* edge of the rectangle in the RTL case. Specifically,
// is the distance leftward from the right edge of the formatting rectangle
// whose width is the paragraph width passed to FormatLine.
//
rect.X = enumerator.CurrentParagraphWidth - rect.Right;
}
rect.X += lineOrigin.X;
rect.Y += lineOrigin.Y;
RectangleGeometry rectangleGeometry = new RectangleGeometry(rect);
if (accumulatedBounds == null)
accumulatedBounds = rectangleGeometry.GetAsPathGeometry();
else
accumulatedBounds = Geometry.Combine(accumulatedBounds, rectangleGeometry, GeometryCombineMode.Union, null);
}
}
}
AdvanceLineOrigin(ref lineOrigin, currentLine);
}
}
}
if (accumulatedBounds == null || accumulatedBounds.IsEmpty())
return null;
return accumulatedBounds;
}
