MSL: row/column major issue.

[urbeller]

the following matrix in HLSL:

float4x3 normalMatrix;

Gets translated to MSL as:

float3x4 normalMatrix;

Although the matrix dimensions are correct, the data does not seem to be copied correctly. For instance, an identity matrix ends up in MSL as:

1	0	0	0
0	0	0	1
0	1	0	0

It looks like we are properly generating a float3x4 matrix but with column-major data layout.

[HansKristian-Work]

float4x3 in HLSL is row-major while MSL layouts are column-major. This is all expected. HLSL compilers to SPIR-V will implicitly transpose and reverse multiplication orders to make this work.

For instance, an identity matrix ends up in MSL as:

Are you sure? How did you generate that identity matrix?

[urbeller]

Hello. Thank you for your reply ! I am aware of the row/column layout difference between the languages. But in this case, I was wondering if there wasn't a bug because the matrix is not squared. In my case, the identity data came from an array like this {1,0,0,0, 0,1,0,0, 0,0,1,0}. would that be possible (and because we are going from 4x3 to a 3x4) that the data gets offsetted ?

[HansKristian-Work]

It depends. If it's an inline array in the shader it's the shader compiler's job to deal with it. You'll have to provide the input HLSL, output SPIR-V and output MSL.