line cross-pull is a set of iMovie transitions (cross-fade, fade-in, fade-out) that divides the picture into a number of lines, and pulls them in opposite directions, revealing the clip underneath. you specify the number of lines (and their thickness), and the direction (horizontal/vertical). the fade-in and fade-out fade from and to a user-defined color.
direction - this pop-up slider defines the direction of the pull: horizontal, or vertical
thickness - this slider controls the thickness of the lines - and as a direct result, how many lines are used in the transition.
color (fade-in, fade-out only) - this controls the color to fade to or fade from.