TSL support for mat4x3 mat4x2

[Makio64]

Description

Currently TSL support mat4 but not particular matrix like mat4x3 mat4x2 etc.. useful in certains cases.

Solution

Add support for particular matrix
mat2x3
mat2x4
mat3x2
mat3x4
mat4x2
mat4x3

Alternatives

not sure how to replace them , of course can use the higher matrix type with empty value but its not optimal.

Additional context

No response

[Spiri0]

I mean, wgsl uses padding by default if you're not using scalars and columns aren't multiples of 2. If I create SBOs with mixed variables, like f32, vec3, and vec4, I still have to reserve 16 bytes, or 4 positions, for each variable. For vec3, wgsl padding to 4. For 1, meaning a scalar, and vec2, wgsl doesn't use any padding. For matrices wgsl stored column by column, wgsl will probably pad anything containing 3 to 4. So there's no benefit there.
But if I really wanted to use these as asymmetric matrices, I could pass the values ​​to a shader using the array node and then create a struct in the shader that has exactly that form.
At least with wgslFn it would work.

[Makio64]

Thanks @Spiri0 , it was very instructive to read !
I encountered this while converting some glsl code which use mat4x2, I still think it might be good to offer the same possibilities between glsl / wgsl & TSL language to make easy conversion & adoption.

[Spiri0]

I wasn't aware that threejs supported non-square matrices (I don't see the technical advantige), but with what I don't know, you can fill the Pacific Ocean and more.
I don't see myself as a suitable user reference anyway, and I'm not going to argue against subjective preferences :)

[Mugen87]

I'm a bit unsure about this feature request. None-square matrices are quite uncommon although I understand the point of retaining original shader code as much as possible.

I have not used the mentioned matrix types so far so I must ask a quite basic question: What vector type is compatible with each matrix type? Doesn't it depend on the multiplication order what vector type you have to use (matrix * column vector vs. row vector * matrix)? If so, is a emulation with square matrices actually mathematical possible?

@WestLangley Can you help us here?

[Spiri0]

An asymmetric matrix cannot be emulated with a square matrix. The matrix multiplication rules apply very strictly. Even if the corresponding rows or columns are filled with zeros, this does not change the shape of the resulting matrix. While the resulting matrix will have zeros in the corresponding result rows or columns, its shape will still strictly depend on the source matrices. Therefore, you have to create the corresponding matrices in the shader.

https://codepen.io/Spiri0/pen/MYWNVvB?editors=0010

If my m matrix in the shader were a n x m = 4 x 4 with all zeros in m = 2 and m = 3 then the result would still be a vec4 and not a vec2 as in the example. So you have to be careful. Matrix multiplications in the shader can be a bit confusing, since vectors are always represented transposed.
However, it's no problem to get the datas into the shader with a square matrix or a buffer or an array and then simply build your desired matrix in the shader using the corresponding elements.

The question that comes to mind is: Does a complex Node solution need to be used for all matrix possibilities?
Is it possible to create asymmetric matrices in Threejs WebGL and send them to a GLSL shader?
I ask because I've never worked with asymmetric matrices myself.
As long as there are no functional limitations on Threejs, I tend to implement things myself. Therefore, I find it difficult to assess the usefulness of such extensions. What I can say with certainty is that you can work with it, but you have to create the matrices yourself.

[Mugen87]

Is it possible to create asymmetric matrices in Threejs WebGL and send them to a GLSL shader?

Math-wise, there are only THREE.Matrix2, THREE.Matrix3 and THREE.Matrix4 classes which assume square matrices. So you can't use three's math lib to make any computations with asymmetric matrices.

If you write a custom shader and use an asymmetric matrix as a uniform type, three.js is not able to update it. AFAICS, this is a general WebGL restriction since the uniformMatrix[234]fv() commands only support square matrices. I've put a live example together to demonstrate the issue:

https://jsfiddle.net/0z6fcd9e/5/

That of course restricts the usage of asymmetric matrices since the only way of using them is to directly embed such matrices (with their values) in the shader code.

[Spiri0]

Ah, I wasn't aware of this restriction. But I've never tried sending asymmetric matrices to the shader either. Then the matter is pretty clear

[Makio64]

Thanks guys, I wanted to use it originally while porting some advanced code to TSL.

In my case, they were always only used as storage for example mat4_2 to return 2 vec4.

Resolving : #30858 should make the job for it, so I propose to close this for now ? @Mugen87

[Mugen87]

Yeah, for the reasons outlined in #30909 (comment), the support for asymmetric matrices will be tricky and feel incomplete anyway.