//------------------------------------------------------------------------------
public static TPolyPolygon OffsetPolygons(TPolyPolygon pts, double delta)
{
//A positive delta will offset each polygon edge towards its left, so
//polygons orientated clockwise (ie outer polygons) will expand but
//inner polyons (holes) will shrink. Conversely, negative deltas will
//offset polygon edges towards their right so outer polygons will shrink
//and inner polygons will expand.
double deltaSq = delta * delta;
TPolyPolygon result = new TPolyPolygon(pts.Count);
for (int j = 0; j < pts.Count; ++j)
{
int highI = pts[j].Count - 1;
TPolygon pg = new TPolygon(highI * 2 + 2);
result.Add(pg);
//to minimize artefacts, strip out those polygons where
//it's shrinking and where its area < Sqr(delta) ...
double area = Area(pts[j]);
if (delta < 0)
{
if (area > 0 && area < deltaSq)
{
highI = 0;
}
}
else if (area < 0 && -area < deltaSq)
{
highI = 0; //nb: a hole if area < 0
}
if (highI < 2)
{
continue;
}
TPolygon normals = new TPolygon(highI + 1);
normals.Add(TClipper.GetUnitNormal(pts[j][highI], pts[j][0]));
for (int i = 1; i <= highI; ++i)
{
normals.Add(TClipper.GetUnitNormal(pts[j][i - 1], pts[j][i]));
}
for (int i = 0; i < highI; ++i)
{
pg.Add(new TDoublePoint(pts[j][i].X + delta * normals[i].X,
pts[j][i].Y + delta * normals[i].Y));
pg.Add(new TDoublePoint(pts[j][i].X + delta * normals[i + 1].X,
pts[j][i].Y + delta * normals[i + 1].Y));
}
pg.Add(new TDoublePoint(pts[j][highI].X + delta * normals[highI].X,
pts[j][highI].Y + delta * normals[highI].Y));
pg.Add(new TDoublePoint(pts[j][highI].X + delta * normals[0].X,
pts[j][highI].Y + delta * normals[0].Y));
//round off reflex angles (ie > 180 deg) unless it's almost flat (ie < 10deg angle) ...
//cross product normals < 0 . reflex angle; dot product normals == 1 . no angle
if ((normals[highI].X * normals[0].Y - normals[0].X * normals[highI].Y) * delta > 0 &&
(normals[0].X * normals[highI].X + normals[0].Y * normals[highI].Y) < 0.985)
{
double a1 = Math.Atan2(normals[highI].Y, normals[highI].X);
double a2 = Math.Atan2(normals[0].Y, normals[0].X);
if (delta > 0 && a2 < a1)
{
a2 = a2 + Math.PI * 2;
}
else if (delta < 0 && a2 > a1)
{
a2 = a2 - Math.PI * 2;
}
TPolygon arc = BuildArc(pts[j][highI], a1, a2, delta);
pg.InsertRange(highI * 2 + 1, arc);
}
for (int i = highI; i > 0; --i)
{
if ((normals[i - 1].X * normals[i].Y - normals[i].X * normals[i - 1].Y) * delta > 0 &&
(normals[i].X * normals[i - 1].X + normals[i].Y * normals[i - 1].Y) < 0.985)
{
double a1 = Math.Atan2(normals[i - 1].Y, normals[i - 1].X);
double a2 = Math.Atan2(normals[i].Y, normals[i].X);
if (delta > 0 && a2 < a1)
{
a2 = a2 + Math.PI * 2;
}
else if (delta < 0 && a2 > a1)
{
a2 = a2 - Math.PI * 2;
}
TPolygon arc = BuildArc(pts[j][i - 1], a1, a2, delta);
pg.InsertRange((i - 1) * 2 + 1, arc);
}
}
}
//finally, clean up untidy corners ...
TClipper c = new TClipper();
c.AddPolyPolygon(result, TPolyType.ptSubject);
if (delta > 0)
{
if (!c.Execute(TClipType.ctUnion, result,
TPolyFillType.pftNonZero, TPolyFillType.pftNonZero))
{
result.Clear();
}
}
else
{
TDoubleRect r = c.GetBounds();
TPolygon outer = new TPolygon(4);
outer.Add(new TDoublePoint(r.left - 10, r.bottom + 10));
outer.Add(new TDoublePoint(r.right + 10, r.bottom + 10));
outer.Add(new TDoublePoint(r.right + 10, r.top - 10));
outer.Add(new TDoublePoint(r.left - 10, r.top - 10));
c.AddPolygon(outer, TPolyType.ptSubject);
if (c.Execute(TClipType.ctUnion, result, TPolyFillType.pftNonZero, TPolyFillType.pftNonZero))
{
result.RemoveAt(0);
}
else
{
result.Clear();
}
}
return(result);
}
//------------------------------------------------------------------------------
public static TPolyPolygon OffsetPolygons(TPolyPolygon pts, double delta)
{
//A positive delta will offset each polygon edge towards its left, so
//polygons orientated clockwise (ie outer polygons) will expand but
//inner polyons (holes) will shrink. Conversely, negative deltas will
//offset polygon edges towards their right so outer polygons will shrink
//and inner polygons will expand.
double deltaSq = delta * delta;
TPolyPolygon result = new TPolyPolygon(pts.Count);
for (int j = 0; j < pts.Count; ++j)
{
int highI = pts[j].Count - 1;
TPolygon pg = new TPolygon(highI * 2 + 2);
result.Add(pg);
//to minimize artefacts, strip out those polygons where
//it's shrinking and where its area < Sqr(delta) ...
double area = Area(pts[j]);
if (delta < 0) { if (area > 0 && area < deltaSq) highI = 0; }
else if (area < 0 && -area < deltaSq) highI = 0; //nb: a hole if area < 0
if (highI < 2) continue;
TPolygon normals = new TPolygon(highI + 1);
normals.Add(TClipper.GetUnitNormal(pts[j][highI], pts[j][0]));
for (int i = 1; i <= highI; ++i)
normals.Add(TClipper.GetUnitNormal(pts[j][i - 1], pts[j][i]));
for (int i = 0; i < highI; ++i)
{
pg.Add(new TDoublePoint(pts[j][i].X + delta * normals[i].X,
pts[j][i].Y + delta * normals[i].Y));
pg.Add(new TDoublePoint(pts[j][i].X + delta * normals[i + 1].X,
pts[j][i].Y + delta * normals[i + 1].Y));
}
pg.Add(new TDoublePoint(pts[j][highI].X + delta * normals[highI].X,
pts[j][highI].Y + delta * normals[highI].Y));
pg.Add(new TDoublePoint(pts[j][highI].X + delta * normals[0].X,
pts[j][highI].Y + delta * normals[0].Y));
//round off reflex angles (ie > 180 deg) unless it's almost flat (ie < 10deg angle) ...
//cross product normals < 0 . reflex angle; dot product normals == 1 . no angle
if ((normals[highI].X * normals[0].Y - normals[0].X * normals[highI].Y) * delta > 0 &&
(normals[0].X * normals[highI].X + normals[0].Y * normals[highI].Y) < 0.985)
{
double a1 = Math.Atan2(normals[highI].Y, normals[highI].X);
double a2 = Math.Atan2(normals[0].Y, normals[0].X);
if (delta > 0 && a2 < a1) a2 = a2 + Math.PI * 2;
else if (delta < 0 && a2 > a1) a2 = a2 - Math.PI * 2;
TPolygon arc = BuildArc(pts[j][highI], a1, a2, delta);
pg.InsertRange(highI * 2 + 1, arc);
}
for (int i = highI; i > 0; --i)
if ((normals[i - 1].X * normals[i].Y - normals[i].X * normals[i - 1].Y) * delta > 0 &&
(normals[i].X * normals[i - 1].X + normals[i].Y * normals[i - 1].Y) < 0.985)
{
double a1 = Math.Atan2(normals[i - 1].Y, normals[i - 1].X);
double a2 = Math.Atan2(normals[i].Y, normals[i].X);
if (delta > 0 && a2 < a1) a2 = a2 + Math.PI * 2;
else if (delta < 0 && a2 > a1) a2 = a2 - Math.PI * 2;
TPolygon arc = BuildArc(pts[j][i - 1], a1, a2, delta);
pg.InsertRange((i - 1) * 2 + 1, arc);
}
}
//finally, clean up untidy corners ...
TClipper c = new TClipper();
c.AddPolyPolygon(result, TPolyType.ptSubject);
if (delta > 0)
{
if (!c.Execute(TClipType.ctUnion, result,
TPolyFillType.pftNonZero, TPolyFillType.pftNonZero)) result.Clear();
}
else
{
TDoubleRect r = c.GetBounds();
TPolygon outer = new TPolygon(4);
outer.Add(new TDoublePoint(r.left - 10, r.bottom + 10));
outer.Add(new TDoublePoint(r.right + 10, r.bottom + 10));
outer.Add(new TDoublePoint(r.right + 10, r.top - 10));
outer.Add(new TDoublePoint(r.left - 10, r.top - 10));
c.AddPolygon(outer, TPolyType.ptSubject);
if (c.Execute(TClipType.ctUnion, result, TPolyFillType.pftNonZero, TPolyFillType.pftNonZero))
result.RemoveAt(0);
else
result.Clear();
}
return result;
}
