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Why does the shear matrix example not use two matrix inputs as per several of the other example nodes in this matrix section? (for example rotation matrix and transform matrix)

https://animation-nodes-manual.readthedocs.io/en/latest/user_guide/nodes/matrix/shear_matrix.html

Just wondered why vector/vertices is used instead.

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Shear transform is a bit different that other transforms like Rotation and Scale. Angles and lengths between points is not preserved for instance. According to Wikipedia Shear is defined as:

In plane geometry, a shear mapping is a linear map that displaces each point in fixed direction, by an amount proportional to its signed distance from the line that is parallel to that direction and goes through the origin. This type of mapping is also called shear transformation, transvection, or just shearing.

So we usually use Shear to distort a group of points. Try to use Shear as the local transform of an object and you will see some unexpected distortion. I am not entirely sure why, but it has to do with how blender interrupt the transformation.

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  • $\begingroup$ Appreciate the reply Omar - though I'm wondering isn't the Scale transformation doing a similar thing by distorting lengths between points? $\endgroup$
    – James Woods
    Apr 26, 2019 at 21:50
  • $\begingroup$ @PeterAskins Sure, I just meant that both of them are not preserved, just an observation. Shear is the only transformation—that we care about—that doesn't preserve the angles. $\endgroup$
    – Omar Emara
    Apr 27, 2019 at 5:39
  • $\begingroup$ Cheers Omar, getting clearer $\endgroup$
    – James Woods
    Apr 27, 2019 at 16:20

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