4v3 matrix support

[d07RiV]

When working with uniform buffer objects in WebGL2, mat3 needs to be laid out as 3 columns of 4 floats, instead of 9 floats like in gl-matrix. This means that there is no supported type in gl-matrix that I can copy into a uniform buffer to satisfy the requirements.

[stefnotch]

According to WebGL2Fundamentals, a mat3 is laid out as 9 floats.

Would you mind providing some code?

[d07RiV]

It matters when using uniform buffer objects to upload entire blocks of uniforms. So if you have something like this in your shader

uniform Matrices {
  mat4 uMVPMatrix;
  mat3 uNormalMatrix;
};

Then in order to upload this block via gl.bindBufferBase/gl.bufferSubData, uNormalMatrix should be laid out as an array of 3 vec4's, according to std140 spec (see rules 4 and 5). The size of this block is 112 bytes, and trying to bind a smaller buffer will result in an error.

(There is no alternative spec, not using std140 means the compiler will choose its own layout which needs to be queried with various functions, and will most likely result in the same matrix stride anyway.)

[stefnotch]

@d07RiV I see. That's a rather tricky issue.

Here are a few possible ways of resolving it:

• Use a mat4 instead
• Don't use a uniform buffer object
• Adding another type mat3v4 to gl-matrix
• A mat3 to mat3v4 function

Are there any options that I forgot?

None of them are optimal, for different reasons.

[d07RiV]

I'm using a mat to mat3v4 function, but that's unnecessary copying operations. Not using UBO is rather counter productive.

I would use mat4, but it lacks some functions such as normalFromMat4.

[stefnotch]

@d07RiV Is there any other function that mat4 is missing other than normalFromMat4?