I have been reading Houdini's OpenCL documentation and haven't really found a way of correctly binding an existing matrix3 attribute.
Trying this when having an matrix3 @xform in the input:


I am getting the "Unknown token 'mat3'" warning. What would be the correct way of doing so?

I'm also trying to figure out some OpenCL matrix stuff and have tried mat3 and mat4 (unsuccessfully).

When binding a volume, if you enable 'Volume transform to Voxel' you get a 4x4 matrix which is a float16...
If you try #bind point &xform float9 it doesn't throw an error or a warning but googling I can't find anything about float9...

from a bit more digging around this appears to work (I'm in the habit of using the name 'transform' for a 3x3 and 'xform' for 4x4):

#bind point &transform float3x3

I'm struggling though to access the components of it. I can get the first 3 with either :

or
- but 3 and upwards doesn't seem to work.
Also work - I thought maybe that would be row 0, col 0 etc but then after those first 3 it doesn't work either...

Btw depending what you're trying to do with the 3x3 I managed to use the rotation part of a 4x4 like this (where xform is a 4x4 point attrib):

At this point I am just trying to get to work with matrices in OpenCL. I mostly want to understand the syntax, specifically in the @-Binding, but I feel like not everything is covered in the documentation. I will be still going to pure OpenCL to get better insights.

Pretty cool findings! Thanks so much. I will post any useful thing I discover here too.

Yes please do, I'll do the same. There's also a bit more info in another thread I started here in case useful:

https://www.sidefx.com/forum/topic/99305/ [www.sidefx.com]

Also here's a thread about using matrices in OpenCL in COPs

https://www.sidefx.com/forum/topic/99150/ [www.sidefx.com]

Try @transform.xx, @transform.yz, @transform.xz

I tried that, doesn't work unfortunately.

@transform.w

nope tried that too

I think your handwriting is irregular

I'm still finding my way around OpenCL so all I can say is what works for me.

.w works for float4 but not for float3x3. I was trying to get at the 3 rows of a 3 x 3 matrix. The docs say there is a mat3, though also -

"There is no native 9-element type. The mat3 we have defined is actually a 12-element type, so care has to be done to move it to or from memory."

If I declare a mat3 inside my kernel I can get at the rows using However if I try to bind a mat3 it gives the warning "Unknown token 'mat3'."
If I bind a float3x3 it doesn't error but using either or just gives me the first element of the matrix, not the first row.

.w errors

I've also recently worked with matrices in opencl houdini context.
Here is some info:
- float3x3 is probably just a bug and interprets as float3 (I can do bind point &P float3whateverand it still works
- mat3 is an alias to float3[3]and mat4 is float16which can be confusing. mat3 is basically an array and mat4 is builtin vector type
- mat3 being an array of float3 should be used carefully. it's not continuous in memory because float3 is actually 4 floats. you can't just copy float[9]for example
- there are many useful functions in matrix.h that compatible with vex row-major matrix, you should check them and use it when you interop with something coming from sops
- to bind 3x3 matrix you should use float9token on binding (which is illegal type as stated in docs so it became float[9]- an array)
- to construct mat3 from float[9]use mat3load

check this simple example above with the same transfrom in vex and opencl