SWMM5 Delphi GUI Uvertex.pas Summary

 Below is a high-level overview of Uvertex.pas, a Delphi unit that manages a linked list of 2D vertex coordinates forming polylines or polygons in EPA SWMM.

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1. Purpose and Structure

The Uvertex.pas unit defines:

1. TVertex record

   • Holds (X, Y) coordinates of a point.
   • Includes a Next pointer to the subsequent vertex, implementing a forward-linked list structure.

2. TVertexList class

   • A linked list of these TVertex nodes, storing vertex coordinates that represent either:
     • A polyline, such as the geometry for a link or conduit, or
     • A polygon, such as the boundary for a subcatchment or storage shape.

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2. Major Components and Methods

2.1 Vertex Management

1. Vfirst, Vcurrent

   • Vfirst: pointer to the first vertex in the list.
   • Vcurrent: pointer to the current vertex in the list, used for insertion or traversal.

2. Add(X, Y: Extended): PVertex

   • Allocates a new vertex, sets its (X, Y) coordinates, then inserts it after Vcurrent.
   • Updates Vcurrent to the new vertex.

3. Delete(aVertex: PVertex): PVertex

   • Removes aVertex from the linked list.
   • Frees the memory allocated for that vertex.
   • Updates Vcurrent to the previous vertex or the new list head.

4. Clear

   • Traverses and deletes all vertices in the list, releasing their memory.

2.2 Traversal and Positioning

1. First / Next

   • First sets Vcurrent to the first vertex and returns it.
   • Next advances Vcurrent to the next vertex in the list and returns it.

2. Find(X1, X2, Y1, Y2: Extended): PVertex

   • Locates the first vertex whose (X, Y) is within the rectangle [X1..X2] x [Y1..Y2].
   • Sets Vcurrent to that vertex if found.

3. Count

   • Returns the total number of vertices in the list.

4. Move(DX, DY: Extended)

   • Adds (DX, DY) to every vertex coordinate in the list, effectively translating the entire shape.

5. Assign(aVlist: TVertexList)

   • Copies all vertices from another TVertexList.

2.3 Specialized Polygon Operations

While TVertexList can store polylines, it also supports polygon operations:

1. AddPolygonVertex

   • Inserts a new vertex midway between Vcurrent and Vcurrent^.Next.
   • Assumes a closed polygon where the last vertex’s Next might circle back to Vfirst.

2. ClearPolygon

   • Removes all vertices except for one, which is set to the shape’s centroid.

3. PolygonCentroid(var X, Y: Extended): Boolean

   • Uses a formula (from Graphics Gems IV) to find the centroid of the polygon.
   • Returns it in (X, Y).
   • Handles edge cases with fewer vertices gracefully.

4. PolygonArea: Extended

   • Computes the signed area of the polygon using a typical cross-product method (again from Graphics Gems IV).
   • Returns the area in positive units (absolute value).

2.4 Additional Utility Methods

1. Reverse

   • Reverses the order of vertices in the list (end becomes start, etc.).

2. Update(X, Y: Extended)

   • Updates the coordinates of Vcurrent without creating a new vertex.

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3. Typical Usage

1. Initializing a shape or link:

   var
     Vlist: TVertexList;
   begin
     Vlist := TVertexList.Create;
     Vlist.Add(100, 200);
     Vlist.Add(150, 250);
     // ...
   end;
   

2. Finding polygons area and centroid, used for subcatchment geometry:

   var
     area, cx, cy: Extended;
   begin
     area := Vlist.PolygonArea;
     Vlist.PolygonCentroid(cx, cy);
   end;
   

3. Editing a shape’s geometry in SWMM’s map via:

   • Inserting or deleting vertices (Add, Delete),
   • Translating the entire shape (Move),
   • Reversing the polyline flow direction (Reverse).

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4. Summary

Uvertex.pas is a lightweight but crucial part of SWMM’s internal geometry handling:

• Implements a singly linked list of (X, Y) vertices,
• Handles geometry-related actions (insert, delete, move),
• Provides basic polygon computations (centroid and area),
• Powers link or subcatchment shapes in the SWMM GUI.

This allows the rest of SWMM (particularly the map form and property editor) to efficiently manage polylines (links) and polygons (subcatchments/storage) with flexible insertion, deletion, and transformations of vertices.