// Simple heuristic procedure for removing holes from a list of polygons
// works by creating a diagonal from the rightmost hole vertex to some visible vertex
// time complexity: O(h*(n^2)), h is the number of holes, n is the number of vertices
// space complexity: O(n)
// params:
// inpolys : a list of polygons that can contain holes
// vertices of all non-hole polys have to be in counter-clockwise order
// vertices of all hole polys have to be in clockwise order
// outpolys : a list of polygons without holes
// Returns true on success, false on failure
private static bool RemoveHoles(TPPLPolyList inpolys, out TPPLPolyList outpolys)
{
TPPLPolyList polys = new TPPLPolyList(inpolys);
// Check for trivial case (no holes)
bool hasholes = false;
foreach (var poly in inpolys)
{
if (poly.IsHole())
{
hasholes = true;
break;
}
}
if (!hasholes)
{
outpolys = new TPPLPolyList(inpolys);
return(true);
}
while (true)
{
int holeIndex = 0;
int polyIndex = 0;
int holepointindex = 0;
int polypointindex = 0;
//find the hole point with the largest x
hasholes = false;
for (int index = 0; index < polys.Count; index++)
{
var poly = polys[index];
if (!poly.IsHole())
{
continue;
}
if (!hasholes)
{
hasholes = true;
holeIndex = index;
holepointindex = 0;
}
for (int i = 0; i < poly.NumPoints; i++)
{
if (poly.GetPoint(i).x > polys[holeIndex].GetPoint(holepointindex).x)
{
holeIndex = index;
holepointindex = i;
}
}
}
if (!hasholes)
{
break;
}
Vector2 holepoint = polys[holeIndex].GetPoint(holepointindex);
Vector2 bestpolypoint = new Vector2();
bool pointfound = false;
for (int index = 0; index < polys.Count; index++)
{
var poly = polys[index];
if (poly.IsHole())
{
continue;
}
for (int i = 0; i < poly.NumPoints; i++)
{
if (poly.GetPoint(i).x <= holepoint.x)
{
continue;
}
if (!InCone(poly.GetPoint((i + poly.NumPoints - 1) % poly.NumPoints),
poly.GetPoint(i),
poly.GetPoint((i + 1) % poly.NumPoints),
holepoint))
{
continue;
}
Vector2 polypoint = poly.GetPoint(i);
if (pointfound)
{
Vector2 v1 = Normalize(polypoint - holepoint);
Vector2 v2 = Normalize(bestpolypoint - holepoint);
if (v2.x > v1.x)
{
continue;
}
}
bool pointvisible = true;
foreach (var poly2 in polys)
{
if (poly2.IsHole())
{
continue;
}
for (int j = 0; j < poly2.NumPoints; j++)
{
Vector2 linep1 = poly2.GetPoint(j);
Vector2 linep2 = poly2.GetPoint((j + 1) % poly2.NumPoints);
if (Intersects(holepoint, polypoint, linep1, linep2))
{
pointvisible = false;
break;
}
}
if (!pointvisible)
{
break;
}
}
if (pointvisible)
{
pointfound = true;
bestpolypoint = polypoint;
polyIndex = index;
polypointindex = i;
}
}
}
if (!pointfound)
{
outpolys = null;
return(false);
}
TPPLPoly newpoly = new TPPLPoly(polys[holeIndex].NumPoints + polys[polyIndex].NumPoints + 2);
int i2 = 0;
for (int i = 0; i <= polypointindex; i++)
{
newpoly[i2] = polys[polyIndex].GetPoint(i);
i2++;
}
for (int i = 0; i <= polys[holeIndex].NumPoints; i++)
{
newpoly[i2] = polys[holeIndex].GetPoint((i + holepointindex) % polys[holeIndex].NumPoints);
i2++;
}
for (int i = polypointindex; i < polys[polyIndex].NumPoints; i++)
{
newpoly[i2] = polys[polyIndex].GetPoint(i);
i2++;
}
polys.RemoveAt(holeIndex);
if (polyIndex > holeIndex)
{
polyIndex--;
}
polys.RemoveAt(polyIndex);
polys.Add(newpoly);
}
outpolys = polys;
return(true);
}
// Triangulates a polygon by ear clipping
// time complexity O(n^2), n is the number of vertices
// space complexity: O(n)
// params:
// poly : an input polygon to be triangulated
// vertices have to be in counter-clockwise order
// triangles : a list of triangles (result)
// returns true on success, false on failure
private static bool Triangulate_EC(TPPLPoly poly, out TPPLPolyList triangles)
{
triangles = new TPPLPolyList();
if (!poly.Valid())
{
return(false);
}
int numvertices = poly.NumPoints;
if (numvertices < 3)
{
return(false);
}
if (numvertices == 3)
{
triangles.Add(poly);
return(true);
}
PartitionVertex[] vertices = new PartitionVertex[numvertices];
PartitionVertex ear = null;
for (int i = 0; i < numvertices; i++)
{
vertices[i] = new PartitionVertex();
}
for (int i = 0; i < numvertices; i++)
{
vertices[i].isActive = true;
vertices[i].p = poly.GetPoint(i);
if (i == (numvertices - 1))
{
vertices[i].next = vertices[0];
}
else
{
vertices[i].next = vertices[i + 1];
}
if (i == 0)
{
vertices[i].previous = vertices[numvertices - 1];
}
else
{
vertices[i].previous = vertices[i - 1];
}
}
for (int i = 0; i < numvertices; i++)
{
UpdateVertex(vertices[i], vertices, numvertices);
}
for (int i = 0; i < numvertices - 3; i++)
{
bool earfound = false;
//find the most extruded ear
for (int j = 0; j < numvertices; j++)
{
if (!vertices[j].isActive)
{
continue;
}
if (!vertices[j].isEar)
{
continue;
}
if (!earfound)
{
earfound = true;
ear = vertices[j];
}
else
{
if (vertices[j].angle > ear.angle)
{
ear = vertices[j];
}
}
}
if (!earfound)
{
return(false);
}
triangles.Add(new TPPLPoly(ear.previous.p, ear.p, ear.next.p));
ear.isActive = false;
ear.previous.next = ear.next;
ear.next.previous = ear.previous;
if (i == numvertices - 4)
{
break;
}
UpdateVertex(ear.previous, vertices, numvertices);
UpdateVertex(ear.next, vertices, numvertices);
}
for (int i = 0; i < numvertices; i++)
{
if (vertices[i].isActive)
{
triangles.Add(new TPPLPoly(vertices[i].previous.p, vertices[i].p, vertices[i].next.p));
break;
}
}
return(true);
}