* Use one point (position) and one direction ( displacement ) vector to define this line
* As we use the texture coordinate as pixel position to calculate random offset,
* the line should passing through rectangle {(0,0),(0,1),(1,0),(1,1)},
* Use one point (position) and one direction ( displacement ) vector to define this line
* As we use the texture coordinate as pixel position to calculate random offset,
* the line should passing through rectangle {(0,0),(0,1),(1,0),(1,1)},