Shape of light beam controlled by a barndoor filter connected to a spotlight
This light filter can only be used with spot lights. Barn doors are opaque moving panels attached to the sides of the light's opening. They are typically used in theatrical and film lighting for additional control over the shape of the light beam. This barndoor filter introduces four barn door flaps. Each barn door flap has three parameters. The first two parameters position the two ends of the flap across the face of the light. The third parameter (edge) controls the softness of the edge. The positions are distances from the respective edge. The edge softness is a ramp width. The ramp starts at one (fully-open) at the barndoor's edge and tapers off to zero based on the edge width in the direction to the perimeter of the spotlight. For example, a flap with coordinates 0.25, 0.25, and an edge of 0.125 will be perfectly "open" at 0.25 and will be perfectly "closed" at 0.375. The edge effect starts at the barndoor edge and works its way outward (*not* inward).
Moves the left corner of the top flap across the face of the light.