Lenticular

An FFGL mixer for Resolume Arena and Avenue, and the fourth mixer in the Stoatworks fleet. A lenticular card is two pictures cut into thin strips and interleaved, A, B, A, B, under a sheet of tiny cylindrical lenses, one lens per strip pair. Each lens focuses the eye onto one point of the print under it, and which strip that point is on depends on the angle the card is seen at. Lenticular models the lens and the print, and what a real card does falls out of it rather than being painted.

The flip: a lens of focal length F focuses rays arriving at angle t onto the print at F tan t from its axis, so the card flips from A to B square on and back again at atan( 1 / 2F ), the edge of the viewing zone. The ghost: a real lens focuses to a spot, not a point, so near the flip the eye sees the mean of the print across it, both pictures at once, and strip bleed softens it further. Moire: if the print's interleave pitch misses the lens pitch, the flip happens in bands of period 1 / | 1/p_L - 1/p_P | that sweep across the picture as the card tilts, which is exactly what a misregistered card looks like.

A viewer at a finite distance sees each column at its own angle, so the flip does not happen all at once: its edge travels across the card, at D sin T from the centre. And each lens shows one sample of its picture, so the picture is stepped at the lens pitch, and the ridges catch the light. Squeeze decides whether each strip holds its picture squeezed, as a real interleave does, or is a window on the picture where it is.

It is chosen as a layer's Blend Mode: the layer below is A, printed in each lens's first strip, and the clip on this layer is B, in the second. The parameter that tilts the card is named Opacity on purpose, because Resolume binds a mixer parameter of that name to the layer's opacity fader, so the fader, or a layer transition, tilts the card from A at 0 to B at 1.