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Blending Matrices

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McCLaw

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Verfasst: Di Mai 03, 2005 19:40

DGL Member

Registriert: Do Dez 11, 2003 13:23
Beiträge: 25
Wohnort: South Africa

Hi All

I am in the process of implementing a Bone Blending animation class, but I have hit a math snag.

I have gotten to the point of getting all the interpolated matrices from the active animations, but I am unsure how to change them according to the weight of each animation, and then how to merge them.

PS: My math knowledge sucks, so speak to me like i'm a three year old :wink:

Any ideas will be greatly appreciated

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Stucuk

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Verfasst: Mi Mai 04, 2005 16:12

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Registriert: Mi Jul 21, 2004 22:39
Beiträge: 360
Wohnort: UK, Scotland

If i remember MD5's correct u add all the bones positions to the vertex's that it effects with the weight scale thing applyed to the bones position.

Code:

 
V := VertexPosition;
 
For x := 0 to NumOfBones do
If Bone Effects Vertex then
V := V + (Bone * Weight);

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Verfasst: Mi Mai 04, 2005 23:25

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Registriert: Sa Jan 22, 2005 21:10
Beiträge: 225

Nearly. In the MD5 format you need to do 2 things:
First calc the skeleton. Usually there are lots of frames, so you actually don't need any interpolation. However, looks like you somehow managed to do that. Than you have to go through the whole skeleton, and multiply the matrices to get the world-space-matrix of each node. (Dunno, whether you already got that part).
Second thing to do is what Stucuk mentioned:

Code:

 
for i := 0 to High(Vertices) do
begin
     Vertices[i].Position := Vec(0, 0, 0); //At least at MD5 the position is given through the weights and the bones' matrices
     For j := 0 to High(Vertices[i].Weights) do
     begin
          Vertices[i].Position := AddVec(Vertices[i].Position + MultVec(AddVec(MultMat(Bones[Vertices[i].Weight[j].Bone].Rot,
                                                                                       Vertices[i].Weight[j].Weight),
                                                                               Bones[Vertices[i].Weight[j].Bone].Pos), 
//I splitted it up into Position and rotation. makes things easier...
                                                                        Vertices[i].Weight[j].Bias)      //And don't forget the bias...
                                        );
     end;
end;
 

This is more or less what I did for MD5s. Worked for most of the models...

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McCLaw

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Verfasst: Do Mai 05, 2005 22:51

DGL Member

Registriert: Do Dez 11, 2003 13:23
Beiträge: 25
Wohnort: South Africa

Thanx for the suggestions

I figured out a way of doing this with Nitrogens help (Thanx Dude)

Code:

 
SetLength(FMergedMatrices,0);
  if Count > 0 then // We have animations to check
  begin
    for i := 0 to Count - 1 do
    begin
      lAnim := Anims[i];
      if lAnim.Active then
      begin
        lAnim.CalulateCurrentBoneMatrix(FCurrentTime); // Get the interpolated matrix list
        { Merge With Other Bone Matrices }
        for j := 0 to Length(lAnim.MergedMatrices) - 1 do
        begin
          lMergedMatrix := lAnim.MergedMatrices[j];
          { If FMergedMatrices is too small, make it bigger}
          if Length(FMergedMatrices) < j + 1 then
          begin
            SetLength(FMergedMatrices,j + 1);
          end;
          { Scale the matrix according to the Influence the animation has on the mesh }
          ScaleMatrix(lMergedMatrix,lAnim.Influence);
          for n := 0 to 3 do
          begin
            // Concatinate the matrix to the other stored matrices
            VectorAdd(lMergedMatrix[n],FMergedMatrices[j][n],FMergedMatrices[j][n]);
          end;
        end;
      end;
    end;
  end;
 

Obviously this in only the first part of the process, I stil need to add individual bone weights into the algo to allow for feather blending.

The current code basically allows any number of interpolated frames in several animations to be blended by their influence (Value between 0 and 1)

I had a look at doing all the calculations per vertex, but that seemed way too expensive.(My thoughts: Rather do a 16 * amount of bones calculation then an undefined number of calculations for any number of vertices in the mesh) and then just apply the resulting matrix to the correct verts in the inverted mesh.

It seems that the same theory would apply to individual bone weights, but I'll only know once I have finished that

PS: I'm using the VectorGeometry.pas file from glscene.

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