This filter creates a linear blur in a direction determined by the “Angle” option. The default direction is horizontal to the right (0.000 degree).
These options are common to GEGL-based filters. Please refer to Section 2, “Common Features”.
In this case, “Length” represents the blur intensity. More Length will result in more blurring.
“Angle” describes the direction of the movement. Thus, a setting of 90 will produce a vertical blur, and a setting of 0 will produce a horizontal blur.