/// <summary>
/// Try to visit all the spans. May be needed in filtering small regions.
/// </summary>
/// <param name="regions">an array of region values</param>
/// <param name="spanRef">The span to start walking from.</param>
/// <param name="dir">The direction to start walking in.</param>
/// <param name="cont">A collection of regions to append to.</param>
private void WalkContour(RegionId[] regions, CompactSpanReference spanRef, Direction dir, List<RegionId> cont)
{
Direction startDir = dir;
int starti = spanRef.Index;
CompactSpan ss = spans[starti];
RegionId curReg = RegionId.Null;
if (ss.IsConnected(dir))
{
int dx = spanRef.X + dir.GetHorizontalOffset();
int dy = spanRef.Y + dir.GetVerticalOffset();
int di = cells[dx + dy * width].StartIndex + CompactSpan.GetConnection(ref ss, dir);
curReg = regions[di];
}
cont.Add(curReg);
int iter = 0;
while (++iter < 40000)
{
CompactSpan s = spans[spanRef.Index];
if (IsSolidEdge(regions, ref spanRef, dir))
{
//choose the edge corner
RegionId r = RegionId.Null;
if (s.IsConnected(dir))
{
int dx = spanRef.X + dir.GetHorizontalOffset();
int dy = spanRef.Y + dir.GetVerticalOffset();
int di = cells[dx + dy * width].StartIndex + CompactSpan.GetConnection(ref s, dir);
r = regions[di];
}
if (r != curReg)
{
curReg = r;
cont.Add(curReg);
}
dir = dir.NextClockwise(); //rotate clockwise
}
else
{
int di = -1;
int dx = spanRef.X + dir.GetHorizontalOffset();
int dy = spanRef.Y + dir.GetVerticalOffset();
if (s.IsConnected(dir))
{
CompactCell dc = cells[dx + dy * width];
di = dc.StartIndex + CompactSpan.GetConnection(ref s, dir);
}
if (di == -1)
{
//shouldn't happen
return;
}
spanRef = new CompactSpanReference(dx, dy, di);
dir = dir.NextCounterClockwise(); //rotate counterclockwise
}
if (starti == spanRef.Index && startDir == dir)
break;
}
//remove adjacent duplicates
if (cont.Count > 1)
{
for (int j = 0; j < cont.Count;)
{
//next element
int nj = (j + 1) % cont.Count;
//adjacent duplicate found
if (cont[j] == cont[nj])
cont.RemoveAt(j);
else
j++;
}
}
}
/// <summary>
/// Helper method for WalkContour function
/// </summary>
/// <param name="sr">The span to get the corner height for.</param>
/// <param name="dir">The direction to get the corner height from.</param>
/// <param name="isBorderVertex">Determine whether the vertex is a border or not.</param>
/// <returns>The corner height.</returns>
private int GetCornerHeight(CompactSpanReference sr, Direction dir, out bool isBorderVertex)
{
isBorderVertex = false;
CompactSpan s = this[sr];
int cornerHeight = s.Minimum;
Direction dirp = dir.NextClockwise(); //new clockwise direction
RegionId[] cornerRegs = new RegionId[4];
Area[] cornerAreas = new Area[4];
//combine region and area codes in order to prevent border vertices, which are in between two areas, to be removed
cornerRegs[0] = s.Region;
cornerAreas[0] = areas[sr.Index];
if (s.IsConnected(dir))
{
//get neighbor span
int dx = sr.X + dir.GetHorizontalOffset();
int dy = sr.Y + dir.GetVerticalOffset();
int di = cells[dx + dy * width].StartIndex + CompactSpan.GetConnection(ref s, dir);
CompactSpan ds = spans[di];
cornerHeight = Math.Max(cornerHeight, ds.Minimum);
cornerRegs[1] = spans[di].Region;
cornerAreas[1] = areas[di];
//get neighbor of neighbor's span
if (ds.IsConnected(dirp))
{
int dx2 = dx + dirp.GetHorizontalOffset();
int dy2 = dy + dirp.GetVerticalOffset();
int di2 = cells[dx2 + dy2 * width].StartIndex + CompactSpan.GetConnection(ref ds, dirp);
CompactSpan ds2 = spans[di2];
cornerHeight = Math.Max(cornerHeight, ds2.Minimum);
cornerRegs[2] = ds2.Region;
cornerAreas[2] = areas[di2];
}
}
//get neighbor span
if (s.IsConnected(dirp))
{
int dx = sr.X + dirp.GetHorizontalOffset();
int dy = sr.Y + dirp.GetVerticalOffset();
int di = cells[dx + dy * width].StartIndex + CompactSpan.GetConnection(ref s, dirp);
CompactSpan ds = spans[di];
cornerHeight = Math.Max(cornerHeight, ds.Minimum);
cornerRegs[3] = ds.Region;
cornerAreas[3] = areas[di];
//get neighbor of neighbor's span
if (ds.IsConnected(dir))
{
int dx2 = dx + dir.GetHorizontalOffset();
int dy2 = dy + dir.GetVerticalOffset();
int di2 = cells[dx2 + dy2 * width].StartIndex + CompactSpan.GetConnection(ref ds, dir);
CompactSpan ds2 = spans[di2];
cornerHeight = Math.Max(cornerHeight, ds2.Minimum);
cornerRegs[2] = ds2.Region;
cornerAreas[2] = areas[di2];
}
}
//check if vertex is special edge vertex
//if so, these vertices will be removed later
for (int j = 0; j < 4; j++)
{
int a = j;
int b = (j + 1) % 4;
int c = (j + 2) % 4;
int d = (j + 3) % 4;
RegionId ra = cornerRegs[a], rb = cornerRegs[b], rc = cornerRegs[c], rd = cornerRegs[d];
Area aa = cornerAreas[a], ab = cornerAreas[b], ac = cornerAreas[c], ad = cornerAreas[d];
//the vertex is a border vertex if:
//two same exterior cells in a row followed by two interior cells and none of the regions are out of bounds
bool twoSameExteriors = RegionId.HasFlags(ra, RegionFlags.Border) && RegionId.HasFlags(rb, RegionFlags.Border) && (ra == rb && aa == ab);
bool twoSameInteriors = !(RegionId.HasFlags(rc, RegionFlags.Border) || RegionId.HasFlags(rd, RegionFlags.Border));
bool intsSameArea = ac == ad;
bool noZeros = ra != 0 && rb != 0 && rc != 0 && rd != 0 && aa != 0 && ab != 0 && ac != 0 && ad != 0;
if (twoSameExteriors && twoSameInteriors && intsSameArea && noZeros)
{
isBorderVertex = true;
break;
}
}
return cornerHeight;
}
