This algorithm reduces scaling distortion on the center of the image
when scaling from ultrawide to wide.
(Jim: edited effect files to prevent an impact in performance for
standard scaling. Now effectively generates an extra pixel shader, and
the extra code is only applied to the DrawUndistort technique, while the
original Draw technique is unaffected due to the compiler automatically
removing unused code branches via the hard-coded boolean value)
From jp9000/obs-studio#762
ab3531caa9