/// <summary>
/// For mesh g, create a new mesh from the passed selected faces,
/// discarding un-referenced data and generating new index, vertex & face buffers.
/// </summary>
public static IGeometryAttributes SelectFaces(this IGeometryAttributes g, IArray <int> faces)
{
// Early exit, if all selected no need to do anything
if (g.NumFaces == faces.Count)
{
return(g);
}
// Early exit, if none selected no need to do anything
if (faces.Count == 0)
{
return(null);
}
// First, get all the indices for this array of faces
var oldIndices = g.GetAttributeIndex();
var oldSelIndices = new int[faces.Count * g.NumCornersPerFace];
// var oldIndices = faces.SelectMany(f => f.Indices());
for (int i = 0; i < faces.Count; i++)
{
for (int t = 0; t < 3; t++)
{
oldSelIndices[i * 3 + t] = oldIndices.Data[faces[i] * g.NumCornersPerFace + t];
}
}
// We need to create list of newIndices, and remapping
// of oldVertices to newVertices
var newIndices = (-1).Repeat(oldSelIndices.Length).ToArray();
// Each index could potentially be in the new mesh
var indexLookup = (-1).Repeat(oldIndices.ElementCount).ToArray();
// Build mapping. For each index, if the vertex it has
// already been referred to has been mapped, use the
// mapped index. Otherwise, remember that we need this vertex
var numUsedVertices = 0;
// remapping from old vert array => new vert array
// Cache built of the old indices of vertices that are used
// should be equivalent to indexLookup.Where(i => i != -1)
var oldVertices = g.GetAttributePosition();
var usedVertices = (-1).Repeat(oldVertices.ElementCount).ToArray();
for (var i = 0; i < oldSelIndices.Length; ++i)
{
var oldIndex = oldSelIndices[i];
var newIndex = indexLookup[oldIndex];
if (newIndex < 0)
{
// remapping from old vert array => new vert array
usedVertices[numUsedVertices] = oldIndex;
newIndex = indexLookup[oldIndex] = numUsedVertices++;
}
newIndices[i] = newIndex;
}
//var faceRemapping = faces.Select(f => f.Index);
var vertRemapping = usedVertices.Take(numUsedVertices).ToIArray();
var cornerRemapping = g.FaceIndicesToCornerIndices(faces);
return(g.VertexAttributes()
.Select(attr => attr.Remap(vertRemapping))
.Concat(g.NoneAttributes())
.Concat(g.FaceAttributes().Select(attr => attr.Remap(faces)))
.Concat(g.EdgeAttributes().Select(attr => attr.Remap(cornerRemapping)))
.Concat(g.CornerAttributes().Select(attr => attr.Remap(cornerRemapping)))
.Concat(g.WholeGeometryAttributes())
.ToGeometryAttributes()
.SetAttribute(newIndices.ToIndexAttribute()));
}
/// <summary> /// Leaves the vertex buffer intact and creates a new geometry that remaps all of the group, corner, and face data. /// The newFaces array is a list of indices into the old face array. /// Note: sub-geometries are lost. /// </summary> public static IGeometryAttributes RemapFaces(this IGeometryAttributes g, IArray <int> faceRemap) => g.RemapFacesAndCorners(faceRemap, g.FaceIndicesToCornerIndices(faceRemap));