In most vector graphic software libraries I can use (3x3) matrices to transform 2D geometry (e.g. scale, rotate, skew). How does a matrix need to look like to transform a 2D rectangle to a symmetrical trapezoid (or equilateral triangle if parameters are taken to the extreme)? What parts of the matrix define which parameters?
2D transformation matrix to make a trapezoid out of a rectangle
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geometry
matrices