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WebGL: hardware skinning with a bone texture


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#1 Chananya Freiman   Members   -  Reputation: 140

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Posted 30 June 2013 - 07:09 PM

I have WebGL code running hardware skinning in a vertex shader for animations, using a uniform array of matrices for my bones.

The problem arises when I don't have enough vector slots, which happens when there are more than 62 bones (I don't control the models or the number of bones, and I've already seen a model with 173 bones, which is crazy).

 

I tried using a float texture to store all my bones in, and fetch them in the shader, but I can't seem to do that correctly.

 

There is no texelFetch in WebGL's version of GLSL, no 1D textures and obviously no texture buffers or uniform buffers.

 

What I tried was creating a X on 1 2D float texture, where X is the number of floats required for all the matrices, feeding it with all the matrices.

 

I send to the shader the size of each matrix and the size of each vector, relative to the size of the texture, so I can get to any matrix with a normal texture fetch.

 

I believe this should work...in theory. But it doesn't.

 

This is the texutre initialization code:

var buffer = new Float32Array(...);
... 
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, buffer.byteLength / 16, 1, 0, gl.RGBA, gl.FLOAT, buffer);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);

And the part of the vertex shader that constructs a matrix from the texture, given a matrix index:

...
uniform sampler2D u_bone_map;
uniform float u_matrix_fraction;
uniform float u_vector_fraction;
...
mat4 boneMatrix(float bone) {
  return mat4(texture2D(u_bone_map, vec2(u_matrix_fraction * bone, 0)),
              texture2D(u_bone_map, vec2(u_matrix_fraction * bone + u_vector_fraction, 0)),
              texture2D(u_bone_map, vec2(u_matrix_fraction * bone + u_vector_fraction * 2.0, 0)),
              texture2D(u_bone_map, vec2(u_matrix_fraction * bone + u_vector_fraction * 3.0, 0)));
}
...

u_matrix_fraction and u_vector_fraction are the relative sizes I wrote above.

E.g., if the texture is 512x1 each matrix is 16/512, and each vector is 4/512, so to get the ith matrix, the code would need to go to i*u_matrix_fraction and grab 4 texels, each the size of u_vector_fraction.

 

These matrices result in my meshes going crazy, so something is wrong, but I am just not sure what.

 

Got any ideas?

 

Thanks for any help.


Edited by Chananya Freiman, 30 June 2013 - 07:12 PM.


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#2 marcClintDion   Members   -  Reputation: 431

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Posted 30 June 2013 - 07:32 PM

I'm intrigued... really, I'm surprised, when I first heard of WebGL I had assumed that texture access in the vertex shader would not be supported. 

.....

Well after a quick two minutes of reading it seems that Chrome and Firefox are not holding firm to the OpenGL E.S. 2.0. spec.  I guess you can do it. 

 

Have you tried printing what you are putting into the texture out to a text file as well so you can see if the data makes sense?  That's usually how I debug.


Consider it pure joy, my brothers and sisters, whenever you face trials of many kinds, because you know that the testing of your faith produces perseverance. Let perseverance finish its work so that you may be mature and complete, not lacking anything.


#3 Chananya Freiman   Members   -  Reputation: 140

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Posted 30 June 2013 - 07:41 PM

I don't have access to files, JavaScript sleep.png

 

In any case, the data is the same data I otherwise use in the matrix uniform array (where it works as expected), so it's correct.

 

There's probably something really stupid and obvious I am doing and not noticing.


Edited by Chananya Freiman, 30 June 2013 - 07:42 PM.


#4 apatriarca   Crossbones+   -  Reputation: 1603

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Posted 01 July 2013 - 01:41 AM

Have you tried using something like the WebGL Inspector ?

#5 Chananya Freiman   Members   -  Reputation: 140

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Posted 01 July 2013 - 07:32 AM

I did not know of the existence of that inspector, I'll check it out.

 

Thanks. smile.png

 

/Edit

 

Thanks a lot, that inspector really helped. Got the skinning working this time!


Edited by Chananya Freiman, 01 July 2013 - 01:54 PM.





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