setToVerticalFlip

Sets this matrix to one that flips and shifts the y-axis. The resultant matrix maps Y=0 to Y=1 and Y=1 to Y=0. All existing values are overwritten. This matrix is usually used to change the coordinate origin from an upper left coordinate origin to a lower left coordinate origin.
This matrix is typically necessary to align the coordinate system of images (top-left origin) with that of OpenGL (bottom-left origin).