When we changed SCNMatrix4 to be column-major instead of row-major in .NET, there
were several other related changes we should have done but didn't do. In particular
we should have made transformation operations based on column-vectors instead of
row-vectors.
In legacy Xamarin, a vector would be transformed by a transformation matrix by doing
matrix multiplication like this:
[ x y z w] * [ 11 21 31 41 ]
| 12 22 32 42 |
| 13 23 33 43 |
[ 14 24 34 41 ]
In this case the vector is a row-vector, and it's the left operand in the multiplication.
When using column-major matrices, we want to use column-vectors, where the vector
is the right operand, like this:
[ 11 21 31 41 ] * [ x ]
| 12 22 32 42 | | y |
| 13 23 33 43 | | z |
[ 14 24 34 41 ] [ w ]
This affects numerous APIs in SCNMatrix4, SCNVector3 and SCNVector4:
* The M## fields have been changed to make the first number the column and the
second number the row, to reflect that it's a column-major matrix (this is
also how it's defined in the native SCNMatrix4 type).
* Functions that return a transformation matrix have been modified to return column-vector
transformers. Technically this means that these matrices are transposed compared
to legacy Xamarin. The functions involved are:
* CreateFromAxisAngle
* CreateRotation[X|Y|Z]
* CreateTranslation
* CreatePerspectiveFieldOfView
* CreatePerspectiveOffCenter
* Rotate
* LookAt
* Combining two column-vector transforming transformation matrices is done by multiplying
them in the reverse order, so the Mult function (and the multiplication operator)
have been modified to multiply the given matrices in the opposite order (this matches
how the SCNMatrix4Mult function does it). To make things clearer I've changed the
parameter names for XAMCORE_5_0.
* Functions that transform a vector using a transformation matrix have been modified
to do a column-vector transformation instead of a row-vector transformation. This
involves the following functions:
* SCNVector3.TransformVector
* SCNVector3.TransformNormal
* SCNVector3.TransformNormalInverse
* SCNVector3.TransformPosition
* SCNVector4.Transform
* Numerous new tests.
Fixes https://github.com/xamarin/xamarin-macios/issues/15094.
42c1c66a14