Last row of Transformation matrix explain?

I used to do some computer graphics stuff but now I couldn’t remember, what exactly does the last row of a 4x4 transfomation matrix do.


If my matrix is from a Block transformation with only move and rotation, I shouldn’t be worry about the last row and just leave it to 0 0 0 1, right?

I think the 3x3 on the top left corner is rotation, the top 3 on the right hand colum is translation. And I think scale is just multiply the 3x3 top left numbers right?

Can someone reminds me which numbers that shear might change? I mostly want to round my rotations to 30 degree and round moves to integer for my Blocks, but I fear that I might shear anything which I dont want. Thanks

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This might help:

Rhino - 2 Matrices and Transformations (