/// <summary>
/// This method extacts skinning information from a skin definition that
/// refers to the given mesh node. If no skin definition is found jointWeights
/// and jointIndices are assigned empty arrays. If there is a valid skin
/// definition this method will output four joint indices per base vertex (Vector4)
/// and three weights (Vector3). If there are more than four joints assigned to a
/// vertex only the four most influencial are selected. The indices in the resulting
/// jointIndices array are referring to positions within the given model's joint
/// collection. 0 refers to the joint at model.Joints[0], 1 refers to the joint at
/// model.Joints[1] and so on. If the model contains no joints this method outputs
/// two empty arrays, just as if no skin defintion existed.
/// </summary>
/// <remarks>The outputted Vector3s for jointWeights represent four normalized weights
/// in three components. The sum of all four weights is 1. The fourth weight is implicitly
/// defined as (1 - X - Y -Z).</remarks>
/// <param name="xmlMeshNode">XML mesh node</param>
/// <param name="model">Model instance with non-empty joint collection</param>
/// <param name="jointIndices">Array of 4-d vectors representing joint indices</param>
/// <param name="jointWeights">Array of 3-d vectors representing their respective weights</param>
protected static void GetJointWeightsAndIndices(XmlNode xmlMeshNode, ColladaModel model,
out Vector4[] jointIndices, out Vector3[] jointWeights)
{
// Look for a skin definition that references this mesh
XmlNode xmlSkin = xmlMeshNode.SelectSingleNode("/COLLADA/library_controllers/" +
"controller/skin[@source='#" + xmlMeshNode.ParentNode.Attributes["id"].Value + "']");
if (xmlSkin == null || model.Joints == null || model.Joints.Count == 0)
{
// no skinning information found
jointIndices = new Vector4[0];
jointWeights = new Vector3[0];
return;
}
// Read number of vertex weight assignments (this is equivalent to the number of base vertices)
XmlNode xmlVertexWeights = xmlSkin.SelectSingleNode("vertex_weights");
int count = int.Parse(xmlVertexWeights.Attributes["count"].Value);
// Read weight source
XmlNode xmlWeightInput = xmlSkin.SelectSingleNode("vertex_weights/input[@semantic='WEIGHT']");
Source weightSource = Source.FromInput(xmlWeightInput, xmlSkin);
var weights = weightSource.GetData <float>();
// Read assignments
XmlNode xmlVertexCount = xmlSkin.SelectSingleNode("vertex_weights/vcount");
XmlNode xmlVertices = xmlSkin.SelectSingleNode("vertex_weights/v");
int[] vcount = XmlUtil.ParseInts(xmlVertexCount.InnerText);
ContentAssert.AreEqual(vcount.Length, count, "vcount.Length");
int[] data = XmlUtil.ParseInts(xmlVertices.InnerText);
// How many items per vertex (this corresponds to the maximum offset of
// all inputs within vertex_weights)
int stride = (from XmlNode node in xmlVertexWeights.SelectNodes("input/@offset")
select int.Parse(node.Value)).Max() + 1;
ContentAssert.IsTrue(stride >= 2, "Invalid weight data");
// It is assumed that joint indices are at offset 0 and their weights at offset 1
// For each base vertex there is one block of joint-weight assigments
jointIndices = new Vector4[count];
jointWeights = new Vector3[count];
bool reachedEnd = false;
for (int i = 0, k = 0; i < count; i++)
{
// There may be more than 4 weights defined
List <JointWeightPair> pairs = new List <JointWeightPair>();
// Add all defined joint-weight pairs
for (int j = 0; j < vcount[i]; j++)
{
int jointIndex = data[k + 0];
int weightIndex = data[k + 1];
pairs.Add(new JointWeightPair(jointIndex, weights[weightIndex]));
k += stride;
}
// Take the four vertices with greatest influence
JointWeightPair[] best = (from pair in pairs
orderby pair.Weight descending
select pair).Take(4).ToArray();
Vector4 curIndices = new Vector4();
Vector4 curWeights = new Vector4();
ContentAssert.IsTrue((vcount[i] <= 4 && best.Length == vcount[i]) ||
best.Length == 4, "Invalid weight data", true);
if (best.Length >= 1)
{
curIndices.X = best[0].JointIndex;
curWeights.X = best[0].Weight;
}
if (best.Length >= 2)
{
curIndices.Y = best[1].JointIndex;
curWeights.Y = best[1].Weight;
}
if (best.Length >= 3)
{
curIndices.Z = best[2].JointIndex;
curWeights.Z = best[2].Weight;
}
if (best.Length == 4)
{
curIndices.W = best[3].JointIndex;
curWeights.W = best[3].Weight;
}
// Normalize weights (sum must be 1)
float sum = curWeights.X + curWeights.Y + curWeights.Z + curWeights.Z;
if (sum > 0)
{
curWeights.X = 1.0f / sum * curWeights.X;
curWeights.Y = 1.0f / sum * curWeights.Y;
curWeights.Z = 1.0f / sum * curWeights.Z;
curWeights.W = 1.0f / sum * curWeights.W;
}
jointIndices[i] = curIndices;
jointWeights[i] = curWeights.XYZ();
if (k == data.Length)
{
reachedEnd = true;
}
}
ContentAssert.IsTrue(reachedEnd, "Not all weights were read", true);
// JointIndices are referring to indices in the joint source
// so every index refers to a name in the source which refers to the
// actual bone
XmlNode xmlInput = xmlSkin.SelectSingleNode("vertex_weights/input[@semantic='JOINT']");
Debug.Assert(xmlInput != null, "No joint input in skin found");
Source jointSource = Source.FromInput(xmlInput, xmlSkin);
var names = jointSource.GetData <string>();
// Create dictionary of model bones with source reference type as key
// (source refers to joints either by name, idref or sidref)
Dictionary <string, Joint> modelJoints = model.Joints.ToDictionary(j =>
j.GetAddressPart(jointSource.ColladaType));
// Check if the names actually refer to the joints in the dictionary
if (modelJoints.ContainsKey(names[0]) == false)
{
Debug.Assert(model.Joints.All(j =>
j.Name != null || j.GlobalID != null || j.ScopedID != null),
"Joints cannot be referenced");
// As of COLLADA 1.4 "name" can refer to name OR sid attribute!
// If the former didn't work try the latter);)
if (jointSource.ColladaType == "name")
{
// Only elements that actually have a sid can be part of the dictionary.
// Elements which don't have a SID usually aren't referenced, so they are
// not needed in the dictionary anyway
modelJoints = model.Joints.Where(j => j.GetAddressPart("sid") != null).
ToDictionary(j => j.GetAddressPart("sid"));
}
// If that still didn't help it's hopeless
if (modelJoints.ContainsKey(names[0]) == false)
{
throw new ApplicationException("Invalid joint references in skin definition");
}
}
try
{
// replace index that points to source with index that points to model's joint
for (int i = 0; i < jointIndices.Length; i++)
{
Vector4 indices = jointIndices[i];
// Find indices in model's joint collection
indices.X = modelJoints[names[(int)indices.X]].Index;
indices.Y = modelJoints[names[(int)indices.Y]].Index;
indices.Z = modelJoints[names[(int)indices.Z]].Index;
indices.W = modelJoints[names[(int)indices.W]].Index;
jointIndices[i] = indices;
}
} catch (IndexOutOfRangeException e)
{
throw new ApplicationException("Invalid joint indices read");
}
// Check data
bool valid = jointIndices.All(v => Math.Abs((v.X + v.Y + v.Z + (1 - v.X - v.Y - v.Z)) - 1) < 0.001f);
ContentAssert.IsTrue(valid, "All joint weights must sum up to 1f");
}
