Fix error in tutorial

[math4origami]

I was trying to figure out how inverse bind pose works, and I was really confused until I realized there's an error here compared to the actual data in "Simple Skin".

Feel free to edit this change to be prettier, but I'd like to bring it up so it can be fixed. Perhaps it will require reediting the image as well.

[javagl]

Thanks for this hint.

The creation of the tutorial, the Simple* models (originally in https://github.com/javagl/gltfTutorialModels/tree/2.0/SimpleSkin , no longer maintained), and the transition between glTF 1.0 and glTF 2.0 interfered a little, so it might be that an error slipped into the model.

Two remarks:

• The SimpleSkin model should also be one of the https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0 , but I noticed that it is not there
• Right now, I have doubts that there should be a translation about -0.5, but admittedly, I cannot be absolutely sure

I'll add the SimpleSkin model ASAP, and cross-check with what is currently shown in the tutorial.

[math4origami]

According to the data in "SimpleSkin", look at min and max in the "accessors" index 3, I see the -0.5:

"max" : [ 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, -0.5, -1.0, 0.0, 1.0 ],
"min" : [ 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, -0.5, -1.0, 0.0, 1.0 ]

The reason I found this is I was trying to follow along with the description in "Skins", and it said the mesh was "with the lower left point at the origin (0,0,0)", and a bunch of data with lots of x=0 coordinates.

But, then the diagram is completely different.

And then, subsequently, all following steps don't make sense to me for how "inverse bind pose" works.

[javagl]

Again, I'll have to analyze this more carefully. One of the changes between glTF 1.0 and 2.0 was that the "Bind Shape Matrix" was omitted, and assumed to be either premultiplied with the mesh data, or postmultiplied to the inverse bind matrices. This is likely where the -0.5 comes from (I just had a look at the 1.0 version of the SimpleSkin example at https://github.com/javagl/gltfTutorialModels/tree/master/SimpleSkin/glTF-Embedded-buffers , and it has different inverse bind matrices). In any case, I'll have to figure out how this can best be conveyed in the images.

[javagl]

OK, I figured this one out ... basically. It was indeed the Bind Shape Matrix that caused some confusion here. The simplest and most appropriate seems to be to update the tutorial, so that the example geometry is not in the x-range (0.0, 1.0) but (-0.5, 0.5).

However, some other (related) issue is now causing some headaches: I wanted to update the SimpleSkin example accordingly. But even though the following file passes validation, none of the viewers (except for my home-brewn one) manages to display the animation:

{
  "accessors" : [ {
    "bufferView" : 0,
    "byteOffset" : 0,
    "componentType" : 5123,
    "count" : 24,
    "type" : "SCALAR",
    "max" : [ 9 ],
    "min" : [ 0 ]
  }, {
    "bufferView" : 1,
    "byteOffset" : 0,
    "componentType" : 5126,
    "count" : 10,
    "type" : "VEC3",
    "max" : [ 0.5, 2.0, 0.0 ],
    "min" : [ -0.5, 0.0, 0.0 ]
  }, {
    "bufferView" : 2,
    "byteOffset" : 0,
    "componentType" : 5123,
    "count" : 10,
    "type" : "VEC4",
    "max" : [ 0, 1, 0, 0 ],
    "min" : [ 0, 1, 0, 0 ]
  }, {
    "bufferView" : 2,
    "byteOffset" : 160,
    "componentType" : 5126,
    "count" : 10,
    "type" : "VEC4",
    "max" : [ 1.0, 1.0, 0.0, 0.0 ],
    "min" : [ 0.0, 0.0, 0.0, 0.0 ]
  }, {
    "bufferView" : 3,
    "byteOffset" : 0,
    "componentType" : 5126,
    "count" : 2,
    "type" : "MAT4",
    "max" : [ 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, -1.0, 0.0, 1.0 ],
    "min" : [ 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, -1.0, 0.0, 1.0 ]
  }, {
    "bufferView" : 4,
    "byteOffset" : 0,
    "componentType" : 5126,
    "count" : 12,
    "type" : "SCALAR",
    "max" : [ 5.5 ],
    "min" : [ 0.0 ]
  }, {
    "bufferView" : 4,
    "byteOffset" : 48,
    "componentType" : 5126,
    "count" : 12,
    "type" : "VEC4",
    "max" : [ 0.0, 0.0, 0.707, 1.0 ],
    "min" : [ 0.0, 0.0, -0.707, 0.707 ]
  } ],
  "animations" : [ {
    "channels" : [ {
      "sampler" : 0,
      "target" : {
        "node" : 2,
        "path" : "rotation"
      }
    } ],
    "samplers" : [ {
      "input" : 5,
      "interpolation" : "LINEAR",
      "output" : 6
    } ]
  } ],
  "asset" : {
    "version" : "2.0"
  },
  "buffers" : [ {
    "uri" : "data:application/gltf-buffer;base64,AAABAAMAAAADAAIAAgADAAUAAgAFAAQABAAFAAcABAAHAAYABgAHAAkABgAJAAgAAAAAvwAAAAAAAAAAAAAAPwAAAAAAAAAAAAAAvwAAAD8AAAAAAAAAPwAAAD8AAAAAAAAAvwAAgD8AAAAAAAAAPwAAgD8AAAAAAAAAvwAAwD8AAAAAAAAAPwAAwD8AAAAAAAAAvwAAAEAAAAAAAAAAPwAAAEAAAAAA",
    "byteLength" : 168
  }, {
    "uri" : "data:application/gltf-buffer;base64,AAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAABAPwAAgD4AAAAAAAAAAAAAQD8AAIA+AAAAAAAAAAAAAAA/AAAAPwAAAAAAAAAAAAAAPwAAAD8AAAAAAAAAAAAAgD4AAEA/AAAAAAAAAAAAAIA+AABAPwAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAA=",
    "byteLength" : 320
  }, {
    "uri" : "data:application/gltf-buffer;base64,AACAPwAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAgL8AAAAAAACAPwAAgD8AAAAAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAIC/AAAAAAAAgD8=",
    "byteLength" : 128
  }, {
    "uri" : "data:application/gltf-buffer;base64,AAAAAAAAAD8AAIA/AADAPwAAAEAAACBAAABAQAAAYEAAAIBAAACQQAAAoEAAALBAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAkxjEPkSLbD8AAAAAAAAAAPT9ND/0/TQ/AAAAAAAAAAD0/TQ/9P00PwAAAAAAAAAAkxjEPkSLbD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAkxjEvkSLbD8AAAAAAAAAAPT9NL/0/TQ/AAAAAAAAAAD0/TS/9P00PwAAAAAAAAAAkxjEvkSLbD8AAAAAAAAAAAAAAAAAAIA/",
    "byteLength" : 240
  } ],
  "bufferViews" : [ {
    "buffer" : 0,
    "byteOffset" : 0,
    "byteLength" : 48,
    "target" : 34963
  }, {
    "buffer" : 0,
    "byteOffset" : 48,
    "byteLength" : 120,
    "target" : 34962
  }, {
    "buffer" : 1,
    "byteOffset" : 0,
    "byteLength" : 320,
    "byteStride" : 16
  }, {
    "buffer" : 2,
    "byteOffset" : 0,
    "byteLength" : 128
  }, {
    "buffer" : 3,
    "byteOffset" : 0,
    "byteLength" : 240
  } ],
  "meshes" : [ {
    "primitives" : [ {
      "attributes" : {
        "POSITION" : 1,
        "JOINTS_0" : 2,
        "WEIGHTS_0" : 3
      },
      "indices" : 0
    } ]
  } ],
  "nodes" : [ {
    "skin" : 0,
    "mesh" : 0
  }, {
    "children" : [ 2 ],
    "translation" : [ 0.0, 1.0, 0.0 ]
  }, {
    "rotation" : [ 0.0, 0.0, 0.0, 1.0 ]
  } ],
  "scenes" : [ {
    "nodes" : [ 0 ]
  } ],
  "skins" : [ {
    "inverseBindMatrices" : 4,
    "joints" : [ 1, 2 ]
  } ]
}

I'll have to sort this out as well...

[3dportable]

Hello, I'm trying to figure out how to display the GLTF file on Android OpenGLES20.
it is required to pass the parameter float [] [] to the shader
I tried it this way,
//joinMatrix
float[][] jointmatrix = new float[12][];
...
glUniformMatrix4fv(rs.u_jointMat, 1, false, jointmatrix, 0);
but the float [] [] array does not want to transmit.
please tell how to pass u_jointMat to shader glTF?

[javagl]

@3dportable This issue is about the glTF tutorial, and this is certainly not the right place to discuss specific Android implementation issues.

But I see...: Where else should you ask?

So for short: The array that is passed to glUniformMatrix4fv must be a 1D array. So if your jointMatrix array should be declared as

float[] jointMatrix = new float[numJoints * 12];

(You could convert your 2D float[][] array into a 1D float[] array immediately before calling glUniformMatrix4fv, but this could cause some memory/performance overhead that you may want to avoid...)

[javagl]

@3dportable I'm not familiar with Android and AndroidStudio in particular. I created JglTF, but was not able to invest much time there recently (and some parts of it would certainly need cleanups, refactorings, tests, and comments). Recently, someone made adaptions for Android and mentioned them in javagl/JglTF#4 (comment) , but I haven't yet found the time to take a closer look at this.

^{(A site note regarding Stack Overflow: A while ago, I would have tried to answer your question (and I've been among the top 0.5% contributors there), but I'm no longer active on the site, because ... all the things you can read on Meta StackExchange...)}

[3dportable]

Thank you, the example for me is complex but very informative. I found a lot of interesting in it. I will study it further. Can you give more details on examples of what is [globalTransformOfNode ^ -1] from tutorial? jointMatrix (j) = globalTransformOfNode ^ -1 * globalTransformOfJointNode * inverseBindMatrix (j) I understand that this is an inverted matrix. But I still can’t understand what kind of variable // globalTransformOfNode is and where to get it. There is code in example. Supplier<float[]> jointMatrixSupplier = MatrixOps .create4x4(nodeModel.createGlobalTransformSupplier()).invert4x4() .multiply4x4(jointNodeModel.createGlobalTransformSupplier()) .multiply4x4(inverseBindMatrixSupplier) .multiply4x4(bindShapeMatrixSupplier) .log("jointMatrix "+j, Level.FINE) .build(); jointMatrixSuppliers.add(jointMatrixSupplier); but it’s very difficult to understand what should be there nodeModel.createGlobalTransformSupplier() This is the only factor that I have not yet participated in the calculations, which is probably why the figure is not displayed correctly. ooo!!! I think I understand this global Transform Of Node That The Mesh Is AttachedTo Thanks for the help

[3dportable]

I want to be able to add mp3 track to each animation GLB.
How to do this?
Please tell about it in the documentation.

[javagl]

@3dportable glTF is intended for graphics. It is unrelated to sound, and specifically to MP3 files. You can add information in the extras, or define your own extension, though.

However, this repository is for the glTF tutorials, and this issue/PR is not a general place to ask random questions (so I'll stop responding to these). A better place for such random, open-end questions might be the forum at https://community.khronos.org/c/gltf-general/45

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[javagl]

This has been resolved by the update from #64