[Webkit-unassigned] [Bug 199215] [WHLSL] Matrix indexing should match HLSL [row][column], but MSL uses [column][row]

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=199215

--- Comment #5 from Justin Fan <justin_fan at apple.com> ---
For Metal Shading Language:

There is no difference between supplying [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16] as a buffer to a shader and telling it to treat it as a float4x4, or using the float4x4() constructor with those values. Result[0] is [1, 2, 3, 4].

If you put [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32] in a buffer, and tell the shader that it's two float4x4s next to each other, the results of buffer1[0] * buffer1[1] are:

538
612
686
760
650
740
830
920
762
868
974
1080
874
996
1118
1240

Thus, the two matrices are
[1 5  9 13]   [17 21 25 29]
[2 6 10 14] * [18 22 26 30]
[3 7 11 15]   [19 23 27 31]
[4 8 12 16]   [20 24 28 32]

and buffer1[0][0] is [1, 2, 3, 4].

This makes sense, as MSL docs imply matrices are built AND stored as Arrays Of Columns Vectors.

Thus the difference remains: HLSL (and thus WHLSL) indexes matrices as Arrays of Row Vectors.

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