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README
LibTessDotNet
Goal
Provide a robust and fast tessellator (polygons with N vertices in the output) for .NET, also does triangulation.
Requirements
 .NET Standard 2.0 (see here for more information)
Features
 Tessellate arbitrary complex polygons
 selfintersecting (see "starintersect" sample)
 with coincident vertices (see "clipper" sample)
 advanced winding rules : even/odd, non zero, positive, negative, winding >= 2 (see "redbookwinding" sample)
 Custom input
 Custom vertex attributes (eg. UV coordinates) with merging callback
 Force orientation of input contour (clockwise/counterclockwise, eg. for GIS systems, see "forcewinding" sample)
 Choice of output
 polygons with N vertices (with N >= 3)
 connected polygons (didn't quite tried this yet, but should work)
 boundary only (to have a basic union of two contours)
 Handles polygons computed with Clipper  an open source freeware polygon clipping library
 Single/Double precision support
Screenshot
Comparison
Build
dotnet build
Example
using LibTessDotNet;
using System;
using System.Drawing;
namespace TessExample
{
class Program
{
// The data array contains 4 values, it's the associated data of the vertices that resulted in an intersection.
private static object VertexCombine(LibTessDotNet.Vec3 position, object[] data, float[] weights)
{
// Fetch the vertex data.
var colors = new Color[] { (Color)data[0], (Color)data[1], (Color)data[2], (Color)data[3] };
// Interpolate with the 4 weights.
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],
(float)colors[0].G * weights[0] + (float)colors[1].G * weights[1] + (float)colors[2].G * weights[2] + (float)colors[3].G * weights[3],
(float)colors[0].B * weights[0] + (float)colors[1].B * weights[1] + (float)colors[2].B * weights[2] + (float)colors[3].B * weights[3],
(float)colors[0].A * weights[0] + (float)colors[1].A * weights[1] + (float)colors[2].A * weights[2] + (float)colors[3].A * weights[3]
};
// Return interpolated data for the new vertex.
return Color.FromArgb((int)rgba[3], (int)rgba[0], (int)rgba[1], (int)rgba[2]);
}
static void Main(string[] args)
{
// Example input data in the form of a star that intersects itself.
var inputData = new float[] { 0.0f, 3.0f, 1.0f, 0.0f, 1.6f, 1.9f, 1.6f, 1.9f, 1.0f, 0.0f };
// Create an instance of the tessellator. Can be reused.
var tess = new LibTessDotNet.Tess();
// Construct the contour from inputData.
// A polygon can be composed of multiple contours which are all tessellated at the same time.
int numPoints = inputData.Length / 2;
var contour = new LibTessDotNet.ContourVertex[numPoints];
for (int i = 0; i < numPoints; i++)
{
// NOTE : Z is here for convenience if you want to keep a 3D vertex position throughout the tessellation process but only X and Y are important.
contour[i].Position = new LibTessDotNet.Vec3(inputData[i * 2], inputData[i * 2 + 1], 0);
// Data can contain any pervertex data, here a constant color.
contour[i].Data = Color.Azure;
}
// Add the contour with a specific orientation, use "Original" if you want to keep the input orientation.
tess.AddContour(contour, LibTessDotNet.ContourOrientation.Clockwise);
// Tessellate!
// The winding rule determines how the different contours are combined together.
// See http://www.glprogramming.com/red/chapter11.html (section "Winding Numbers and Winding Rules") for more information.
// If you want triangles as output, you need to use "Polygons" type as output and 3 vertices per polygon.
tess.Tessellate(LibTessDotNet.WindingRule.EvenOdd, LibTessDotNet.ElementType.Polygons, 3, VertexCombine);
// Same call but the last callback is optional. Data will be null because no interpolated data would have been generated.
//tess.Tessellate(LibTessDotNet.WindingRule.EvenOdd, LibTessDotNet.ElementType.Polygons, 3); // Some vertices will have null Data in this case.
Console.WriteLine("Output triangles:");
int numTriangles = tess.ElementCount;
for (int i = 0; i < numTriangles; i++)
{
var v0 = tess.Vertices[tess.Elements[i * 3]].Position;
var v1 = tess.Vertices[tess.Elements[i * 3 + 1]].Position;
var v2 = tess.Vertices[tess.Elements[i * 3 + 2]].Position;
Console.WriteLine("#{0} ({1:F1},{2:F1}) ({3:F1},{4:F1}) ({5:F1},{6:F1})", i, v0.X, v0.Y, v1.X, v1.Y, v2.X, v2.Y);
}
Console.ReadLine();
}
}
}
Notes
 When using
ElementType.BoundaryContours
,Tess.Elements
will contain a list of ranges[startVertexIndex, vertexCount]
. Those ranges are to used withTess.Vertices
.
TODO
 No allocations with the same input twice, all coming from pool
 Any suggestions are welcome ;)
License
SGI FREE SOFTWARE LICENSE B (Version 2.0, Sept. 18, 2008) More information in LICENSE.txt.
Links
 Reference implementation  the original SGI reference implementation
 libtess2  Mikko Mononen cleaned up the original GLU tesselator
 Poly2Tri  another triangulation library for .NET (other ports also available)
 Does not support polygons from Clipper, more specifically vertices with same coordinates (coincident)
 Clipper  an open source freeware polygon clipping library
*Note that all licence references and agreements mentioned in the LibTessDotNet README section above
are relevant to that project's source code only.