1. distortion - a quadric distortion that affects the image 2. cubic_distortion - a cubic distortion that also affects the image
Both can compensate each other by setting one of the distortion factors to a negative value. (e.g. 1.0 and -1.0)
3. distort_corner - only affects the corners of the screen not the image itself.
This is the setting on that round_corner and smooth_border are applied. smooth_border only works in combination with round_corner, which means that the maximum used value of smooth_border is the current value of round_corner.