public Vertex(Location l, VertexCategory cat)
{
Loc = l;
Category = cat;
if (cat == VertexCategory.Exit && l.HasExitCoords)
{
RegionId = GetRegionId(l.ExitCoords);
}
else
{
RegionId = GetRegionId(l.Coords);
}
}
public void Move(bool emitPreviousEdge)
{
VertexCategory startVertexCategory =
CreateVertexCategory(this.PreviousEdge.EdgeCategory, this.CurrentEdge.EdgeCategory);
VertexCategory endVertexCategory =
CreateVertexCategory(this.CurrentEdge.EdgeCategory, this.NextEdge.EdgeCategory);
EdgeData.ApplyVertexCategory(startVertexCategory, ref this.PreviousEdge, ref this.CurrentEdge);
EdgeData.ApplyVertexCategory(endVertexCategory, ref this.CurrentEdge, ref this.NextEdge);
if (emitPreviousEdge)
{
this.PreviousEdge.EmitScanEdge(this.output, ref this.EdgeCounter);
}
this.PreviousEdge = this.CurrentEdge;
this.CurrentEdge = this.NextEdge;
}
public static void ApplyVertexCategory(
VertexCategory vertexCategory,
ref EdgeData fromEdge,
ref EdgeData toEdge)
{
// On PolygonScanner needs to handle intersections at edge connections (vertices) in a special way:
// - We need to make sure we do not report ("emit") an intersection point more times than necessary because we detected the intersection at both edges.
// - We need to make sure we we emit proper intersection points when scanning through a horizontal line
// In practice this means that vertex intersections have to emitted: 0-2 times in total:
// - Do not emit on vertex of collinear edges
// - Emit 2 times if:
// - One of the edges is horizontal
// - The corner is concave
// (The reason for tis rule is that we do not scan horizontal edges)
// - Emit once otherwise
// Since PolygonScanner does not process vertices, only edges, we need to define arbitrary rules
// about WHERE (on which edge) do we emit the vertex intersections.
// For visualization of the rules see:
// PoygonScanning.MD
// For an example, see:
// ImageSharp.Drawing.Tests/Shapes/Scan/SimplePolygon_AllEmitCases.png
switch (vertexCategory)
{
case VertexCategory.UpUp:
// 0, 1
toEdge.emitStart = 1;
break;
case VertexCategory.UpDown:
// 1, 1
toEdge.emitStart = 1;
fromEdge.emitEnd = 1;
break;
case VertexCategory.UpLeft:
// 2, 0
fromEdge.emitEnd = 2;
break;
case VertexCategory.UpRight:
// 1, 0
fromEdge.emitEnd = 1;
break;
case VertexCategory.DownUp:
// 1, 1
toEdge.emitStart = 1;
fromEdge.emitEnd = 1;
break;
case VertexCategory.DownDown:
// 0, 1
toEdge.emitStart = 1;
break;
case VertexCategory.DownLeft:
// 1, 0
fromEdge.emitEnd = 1;
break;
case VertexCategory.DownRight:
// 2, 0
fromEdge.emitEnd = 2;
break;
case VertexCategory.LeftUp:
// 0, 1
toEdge.emitStart = 1;
break;
case VertexCategory.LeftDown:
// 0, 2
toEdge.emitStart = 2;
break;
case VertexCategory.LeftLeft:
// 0, 0 - collinear
break;
case VertexCategory.LeftRight:
// 0, 0 - collinear
break;
case VertexCategory.RightUp:
// 0, 2
toEdge.emitStart = 2;
break;
case VertexCategory.RightDown:
// 0, 1
toEdge.emitStart = 1;
break;
case VertexCategory.RightLeft:
// 0, 0 - collinear
break;
case VertexCategory.RightRight:
// 0, 0 - collinear
break;
}
}
