LibTessDotNet

When tessellating, new vertices are often created at intersection points. To preserve or interpolate custom data (like UV coordinates or colors) associated with the original vertices, provide a combining callback to the Tessellate method.

Signature pattern: object VertexCombine(Vec3 position, object[] data, float[] weights)

• position: The position of the new vertex.
• data: An array of the Data objects from the original vertices that contributed to this intersection.
• weights: An array of weights used to interpolate the data.

Return the interpolated object (e.g., a new Color or a new UV struct) to be assigned to the new vertex's Data property.

private static object VertexCombine(LibTessDotNet.Vec3 position, object[] data, float[] weights)
{
    // Example: Interpolating colors
    var colors = new Color[] { (Color)data[0], (Color)data[1], (Color)data[2], (Color)data[3] };
    var rgba = new float[] {
        (float)colors[0].R * weights[0] + (float)colors[1].R * weights[1] + (float)colors[2].R * weights[2] + (float)colors[3].R * weights[3],
        // ... (repeat for G, B, A)
    };
    return Color.FromArgb((int)rgba[3], (int)rgba[0], (int)rgba[1], (int)rgba[2]);
}

LibTessDotNet is a fast and robust tessellator for .NET that converts complex polygons into simpler polygons or triangles. It supports self-intersecting polygons, coincident vertices, and various winding rules (even/odd, non-zero, etc.).

To use the library, follow these steps:

1. Create an instance of LibTessDotNet.Tess.
2. Define your vertices using ContourVertex arrays. Each vertex requires a Position (using Vec3). You can optionally attach custom data to the Data property.
3. Add contours to the tessellator using AddContour. You can specify the orientation (e.g., Clockwise, CounterClockwise, or Original).
4. Call Tessellate specifying the WindingRule, the ElementType (e.g., Polygons), the number of vertices per element, and an optional vertex combining callback.
5. Access the resulting geometry via tess.Vertices and tess.Elements.

Note: If you use ElementType.BoundaryContours, tess.Elements will contain ranges in the format [startVertexIndex, vertexCount] instead of direct indices.

using LibTessDotNet;
using System;
using System.Drawing;

// ... (VertexCombine implementation) ...

static void Main(string[] args)
{
    var inputData = new float[] { 0.0f, 3.0f, -1.0f, 0.0f, 1.6f, 1.9f, -1.6f, 1.9f, 1.0f, 0.0f };
    var tess = new LibTessDotNet.Tess();

    int numPoints = inputData.Length / 2;
    var contour = new LibTessDotNet.ContourVertex[numPoints];
    for (int i = 0; i < numPoints; i++)
    {
        contour[i].Position = new LibTessDotNet.Vec3(inputData[i * 2], inputData[i * 2 + 1], 0);
        contour[i].Data = Color.Azure;
    }

    tess.AddContour(contour, LibTessDotNet.ContourOrientation.Clockwise);

    // Tessellate into triangles (3 vertices per polygon)
    tess.Tessellate(LibTessDotNet.WindingRule.EvenOdd, LibTessDotNet.ElementType.Polygons, 3, VertexCombine);

    // Access results
    for (int i = 0; i < tess.ElementCount; i++)
    {
        var v0 = tess.Vertices[tess.Elements[i * 3]].Position;
        // ...
    }
}