Relay

An FFGL mixer for Resolume Arena and Avenue, and the third mixer in the Stoatworks fleet. A cheap video switcher of the analogue era, a SCART box or an old routing switcher, cut with a relay, and each of the relay's parts did something to the picture, because a video frame is scanned in time and a relay's events happen in milliseconds: about fifteen lines each.

The coil has hysteresis: it pulls in at one voltage and drops out at a much lower one. The layer's own opacity fader is the coil voltage (Resolume binds a mixer parameter named Opacity to it), so the fader cuts to B on the way up past Pull-in and back to A on the way down past Drop-out, and nothing in between is a dissolve. The contacts bounce: when the armature moves, the moving contact leaves A, flies to B, hits, rebounds and hits again, each flight shorter by the coefficient of restitution, so the frame the switch lands on shows horizontal bands of A, black and B at the scanlines the bounce times set, cut mid-line at the pixel where the contact landed.

The receiver re-locks: if the two sources are not genlocked, the new source's field timing is somewhere else, and the monitor's vertical PLL pulls it in as a second-order step response, so the picture rolls and settles, overshooting if the loop is underdamped. And the open contact is a small capacitor, so the unselected input leaks through it high-passed, rising 6 dB an octave: its edges ghost faintly into the selected picture. A good router switched in the vertical interval, and Switch Point set to Vert Interval is that cure.

The relay runs on the CPU in double, in seconds of real elapsed time; the shader only asks, for each pixel, which line and how far along it, and therefore which contact the relay was on. It is chosen as a layer's Blend Mode: the layer below is A, and the clip on this layer is B, which the energised coil selects.