private void BuildIntersectionList(float bottom, float top)
{
Debug.Assert(m_intersectionList.Count == 0);
float dy = top - bottom;
float invDy = 1.0f / dy;
SortedEdgeEntry entry = new SortedEdgeEntry();
GetSortedEdgeEntry(bottom, top, dy, 0, ref entry);
m_sortedEdgeList.Add(entry);
for (int i = 1; i < m_activeEdgeList.Count; ++i)
{
GetSortedEdgeEntry(bottom, top, dy, i, ref entry);
int j = m_sortedEdgeList.Count - 1;
while (j >= 0)
{
SortedEdgeEntry otherEntry = m_sortedEdgeList[j];
if (CompareSortedEdgeEntries(ref otherEntry, ref entry) == -1) break;
float x, y;
/*if (entry.DX - otherEntry.DX == 0.0f)
{
x = entry.XCoord + entry.DX * 0.5f;
y = (bottom + top) * 0.5f;
}
else
{*/
float invDxDiff = 1.0f / (entry.DX - otherEntry.DX);
y = (otherEntry.QNumerator - entry.QNumerator) * invDxDiff;
x = entry.DX * invDy * y + entry.QNumerator * invDy;
Debug.Assert(Math.Abs(otherEntry.DX * invDy * y + otherEntry.QNumerator * invDy - x) < 0.001f);
//}
IntersectionListEntry intersection = new IntersectionListEntry();
intersection.RIndex = entry.Index;
intersection.LIndex = otherEntry.Index;
intersection.X = x;
intersection.Y = y;
InsertIntersection(ref intersection);
--j;
}
m_sortedEdgeList.Insert(j + 1, entry);
}
m_sortedEdgeList.Clear();
}
private SortedEdgeEntry GetSortedEdgeEntry(float bottom, float top, float dy, int i, ref SortedEdgeEntry entry)
{
var edge = m_activeEdgeList[i];
entry.Index = i;
if (edge.TopY == top)
{
MyPolygon.Vertex vert;
if (edge.Kind == PolygonType.SUBJECT)
{
m_polyA.GetVertex(edge.TopVertexIndex, out vert);
}
else
{
m_polyB.GetVertex(edge.TopVertexIndex, out vert);
}
entry.XCoord = vert.Coord.X;
}
else
{
entry.XCoord = edge.CalculateX(dy);
}
entry.DX = entry.XCoord - edge.BottomX;
entry.Kind = edge.Kind;
entry.QNumerator = edge.CalculateQNumerator(bottom, top, entry.XCoord);
Debug.Assert(edge.TopY != bottom);
return entry;
}
private static int CompareSortedEdgeEntries(ref SortedEdgeEntry entry1, ref SortedEdgeEntry entry2)
{
// Sorting rules:
// 1.) sort by X coordinate
// 2.) sort by type of input polygon
// 3.) sort by DXdy value (or in this case, only DX)
if (entry1.XCoord < entry2.XCoord)
{
return -1;
}
else if (entry1.XCoord == entry2.XCoord)
{
if (entry1.Kind == entry2.Kind)
{
Debug.Assert(entry1.DX >= entry2.DX, "Overtaking a sorted edge entry that should be processed after us. This shouldn't happen!");
Debug.Assert(entry1.DX > entry2.DX, "Overlapping edge in an input polygon!");
return 1;
}
else if (entry1.Kind == PolygonType.CLIP)
{
return -1;
}
}
return 1;
}
